docs(self-surfacing): derive groups are drift not audit material — shape-accounting + reusing-code skills, static floor, plugin README (after-write hook), api-reference rows (#2902, milestone 299 step 4)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -4,7 +4,7 @@ A self-hosted work system-of-record for software projects, built to be driven by
 
 ## Features
 
-Notes and tasks with a Markdown editor, sub-tasks, milestones, issues, and kanban project workspaces. Stored processes, an engineering rulebook system, and semantic search with proactive knowledge-injection into Claude's context. A knowledge graph, per-user/group sharing, and a built-in MCP server (`/mcp`) plus a bundled Claude Code plugin so Claude can record and recall your work directly.
+Notes and tasks with a Markdown editor, sub-tasks, milestones, issues, and kanban project workspaces. Stored processes, an engineering rulebook system (with an inception step that decides what each project inherits), and semantic search with proactive knowledge-injection into Claude's context. A knowledge graph, per-user/group sharing, and a built-in MCP server (`/mcp`) plus a bundled Claude Code plugin so Claude can record and recall your work directly.
 
 ## Quick Start
 

alembic/versions/0084_code_shape_uses.py

@@ -5,9 +5,9 @@ Revises: 0083
 Create Date: 2026-08-21
 
 A ledger row carries ONE snippet_id: what shape this is (instance/variant of
-a canon). But a shape can also CALL several canonical helpers — a service
+a canon). But a shape can also CALL several canonical helpers — e.g. a
-function that is an instance of the service-function convention and a
+service function both conforming to the service-function convention and
-consumer of hash_token. The 2026-08 audit had to pick one; hook evidence
+consuming hash_token. The 2026-08 audit had to pick one; hook evidence
 ("pulled #N then wrote code referencing it") was stamped as instance when it
 is a uses fact. This table holds the many-valued relation: shape → snippet,
 with the basis and the evidence. Cascades with the shape and the snippet.

alembic/versions/0085_project_inception.py

@@ -0,0 +1,74 @@
+"""Project inception: the decision record + always-on rulebook exclusions (milestone 297)
+
+Revision ID: 0085
+Revises: 0084
+Create Date: 2026-08-22
+
+`projects.inception` is the WHY a project inherits what it does — NULL until
+someone decides, at which point enter_project stops asking. The new
+association `project_rulebook_exclusions` is the opt-out of a whole always-on
+rulebook for one project (the sibling of the rule/topic suppressions).
+
+Backfill: every project that exists when this runs is stamped
+via="legacy" with its CURRENT standing (no exclusions, its subscriptions,
+its design_system_id, no seed) — so the ask fires only for projects created
+after the step shipped, and nothing a running install relies on changes.
+"""
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+revision = "0085"
+down_revision = "0084"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "projects",
+        sa.Column("inception", postgresql.JSONB(), nullable=True),
+    )
+    op.create_table(
+        "project_rulebook_exclusions",
+        sa.Column(
+            "project_id", sa.BigInteger(),
+            sa.ForeignKey("projects.id", ondelete="CASCADE"),
+            primary_key=True, nullable=False,
+        ),
+        sa.Column(
+            "rulebook_id", sa.BigInteger(),
+            sa.ForeignKey("rulebooks.id", ondelete="CASCADE"),
+            primary_key=True, nullable=False,
+        ),
+        sa.Column(
+            "created_at", sa.DateTime(timezone=True),
+            server_default=sa.text("now()"), nullable=False,
+        ),
+    )
+    # Legacy stamp: what each existing project inherits today, recorded as a
+    # decision so the inception ask does not fire on a project that has been
+    # running for months.
+    op.execute(sa.text("""
+        UPDATE projects p SET inception = jsonb_build_object(
+            'via', 'legacy',
+            'decided_at', to_jsonb(now()),
+            'decided_by', NULL,
+            'choices', jsonb_build_object(
+                'exclude_always_on_rulebooks', '[]'::jsonb,
+                'subscribe_rulebooks', COALESCE(
+                    (SELECT jsonb_agg(s.rulebook_id ORDER BY s.rulebook_id)
+                       FROM project_rulebook_subscriptions s
+                      WHERE s.project_id = p.id),
+                    '[]'::jsonb),
+                'design_system_id', to_jsonb(p.design_system_id),
+                'seed_systems', false
+            )
+        )
+        WHERE p.inception IS NULL
+    """))
+
+
+def downgrade() -> None:
+    op.drop_table("project_rulebook_exclusions")
+    op.drop_column("projects", "inception")

docs/api-reference.md

@@ -76,7 +76,9 @@ endpoint at `/mcp`, not these REST routes.
 | Method | Path | Description |
 |--------|------|-------------|
 | GET / POST | `/api/projects` | List (owned + shared) / create |
-| GET / PATCH / DELETE | `/api/projects/:id` | Read (with `milestone_summary`) / update / delete |
+| GET / PATCH / DELETE | `/api/projects/:id` | Read (with `milestone_summary`, `inception`) / update / delete |
+| POST | `/api/projects/:id/inception` | Record what the project inherits `{choices: {exclude_always_on_rulebooks, subscribe_rulebooks, design_system_id, seed_systems}}` (owner-only; `POST /api/projects` accepts the same under `inception`) |
+| GET | `/api/projects/:id/inception/defaults` | What binds if nobody decides — the inception card's payload |
 | GET | `/api/projects/:id/notes` | Notes + tasks in this project |
 | GET / POST | `/api/projects/:id/milestones` | List / create milestones |
 | GET / PATCH / DELETE | `/api/projects/:id/milestones/:mid` | Read / update / delete |
@@ -118,6 +120,7 @@ endpoint at `/mcp`, not these REST routes.
 | POST | `/api/projects/:id/rules` | Create a project-scoped rule |
 | POST / DELETE | `/api/projects/:id/suppressions/rules/:rid` | Suppress / unsuppress a rule |
 | POST / DELETE | `/api/projects/:id/suppressions/topics/:tid` | Suppress / unsuppress a topic |
+| POST / DELETE | `/api/projects/:id/exclusions/rulebooks/:rid` | Exclude / include an always-on rulebook for this project (inception) |
 
 ## Sharing
 
@@ -169,6 +172,8 @@ endpoint at `/mcp`, not these REST routes.
 | GET | `/api/plugin/context` | SessionStart context payload (rules + active-project) |
 | GET | `/api/plugin/retrieve` | Title-first knowledge-injection candidates |
 | GET | `/api/plugin/processes` | Stored Processes for skill-stub sync |
+| GET | `/api/plugin/prior-art` | Write-path hint for the plugin hooks (params: `path`, `code`, `repo`, `shapes`, `exclude_ids`, `exclude_sync_ids`, `exclude_derive`); returns `context`, `note_ids`, `sync_note_ids`, `stamped`, `divergence`, `derive`, `derive_keys` |
+| GET / POST | `/api/projects/<id>/coverage`, `…/coverage/refresh` | Shape-ledger accounting (`pattern_coverage` line, counts, `derive_groups`, `derive_new`, `divergence`, `recheck`) |
 | GET / PUT | `/api/plugin/marketplace-url` | Read / set the plugin marketplace URL |
 
 ## Dashboard, Export, Trash, Users

frontend/src/api/inception.ts

@@ -0,0 +1,42 @@
+/** Project inception (milestone 297): what a project was decided to inherit. */
+import { apiGet, apiPost } from "@/api/client";
+
+export interface InceptionChoices {
+  exclude_always_on_rulebooks: number[];
+  subscribe_rulebooks: number[];
+  design_system_id: number | null;
+  seed_systems: boolean;
+}
+
+export interface InceptionRecord {
+  decided_at: string;
+  decided_by: number | null;
+  via: "mcp" | "ui" | "legacy";
+  choices: InceptionChoices;
+}
+
+export interface InceptionDefaults {
+  always_on_rulebooks: { id: number; title: string }[];
+  other_rulebooks: { id: number; title: string }[];
+  excluded_always_on: { id: number; title: string }[];
+  subscribed_rulebooks: { id: number; title: string }[];
+  design_system_id: number | null;
+  design_systems: { id: number; title: string }[];
+  systems: number;
+}
+
+export interface InceptionDecision {
+  project_id: number;
+  inception: InceptionRecord;
+  effects: { excluded: number[]; subscribed: number[]; design_system_id: number | null; systems_seeded: string[] };
+}
+
+export const emptyChoices = (): InceptionChoices => ({
+  exclude_always_on_rulebooks: [], subscribe_rulebooks: [], design_system_id: null, seed_systems: false,
+});
+
+export const fetchInceptionDefaults = (projectId: number) =>
+  apiGet<InceptionDefaults>(`/api/projects/${projectId}/inception/defaults`);
+
+export const decideInception = (projectId: number, choices: InceptionChoices) =>
+  apiPost<InceptionDecision>(`/api/projects/${projectId}/inception`, { choices });

frontend/src/api/rulebooks.ts

@@ -71,6 +71,8 @@ export interface ApplicableRules {
   }[];
   truncated: boolean;
   subscribed_rulebooks: { id: number; title: string }[];
+  /** Always-on rulebooks this project opted out of at inception (milestone 297). */
+  excluded_always_on: { id: number; title: string }[];
 }
 
 // ── Rulebooks ───────────────────────────────────────────────────────
@@ -181,3 +183,14 @@ export async function suppressTopicForProject(projectId: number, topicId: number
 export async function unsuppressTopicForProject(projectId: number, topicId: number): Promise<void> {
   return apiDelete(`/api/projects/${projectId}/suppressions/topics/${topicId}`);
 }
+
+// ── Always-on exclusions (milestone 297) ────────────────────────────────────
+
+export async function excludeAlwaysOnRulebook(projectId: number, rulebookId: number): Promise<void> {
+  await apiPost(`/api/projects/${projectId}/exclusions/rulebooks/${rulebookId}`, {});
+}
+
+export async function includeAlwaysOnRulebook(projectId: number, rulebookId: number): Promise<void> {
+  await apiDelete(`/api/projects/${projectId}/exclusions/rulebooks/${rulebookId}`);
+}
+

frontend/src/components/InceptionCard.vue

@@ -0,0 +1,189 @@
+<script setup lang="ts">
+/**
+ * The inception form (milestone 297): "what does this project inherit?"
+ *
+ * Two homes, one component. mode="create" rides the New-project modal's
+ * second step and only emits the choices (the project does not exist yet);
+ * mode="decide" sits on ProjectView for an undecided project, loads that
+ * project's current defaults, and records the decision itself.
+ */
+import { computed, onMounted, ref, watch } from "vue";
+import { apiErrorMessage } from "@/api/client";
+import { fetchDesignSystems } from "@/api/designSystems";
+import {
+  decideInception, emptyChoices, fetchInceptionDefaults,
+  type InceptionChoices, type InceptionDecision, type InceptionDefaults,
+} from "@/api/inception";
+import { listRulebooks } from "@/api/rulebooks";
+
+const props = withDefaults(defineProps<{
+  mode: "create" | "decide";
+  projectId?: number;
+  choices?: InceptionChoices;
+}>(), { projectId: 0, choices: undefined });
+
+const emit = defineEmits<{
+  "update:choices": [value: InceptionChoices];
+  decided: [decision: InceptionDecision];
+}>();
+
+const local = ref<InceptionChoices>(props.choices ? { ...props.choices } : emptyChoices());
+const alwaysOn = ref<{ id: number; title: string }[]>([]);
+const others = ref<{ id: number; title: string }[]>([]);
+const designSystems = ref<{ id: number; title: string }[]>([]);
+const systemsCount = ref(0);
+const loading = ref(true);
+const saving = ref(false);
+const error = ref("");
+
+function emitChoices() {
+  emit("update:choices", { ...local.value });
+}
+watch(local, emitChoices, { deep: true });
+
+async function load() {
+  loading.value = true;
+  error.value = "";
+  try {
+    if (props.mode === "decide" && props.projectId) {
+      const d: InceptionDefaults = await fetchInceptionDefaults(props.projectId);
+      alwaysOn.value = d.always_on_rulebooks;
+      others.value = d.other_rulebooks;
+      designSystems.value = d.design_systems;
+      systemsCount.value = d.systems;
+      // Start from what stands today so "record" without changes is a true inherit-all.
+      local.value = {
+        exclude_always_on_rulebooks: d.excluded_always_on.map((r) => r.id),
+        subscribe_rulebooks: d.subscribed_rulebooks.map((r) => r.id),
+        design_system_id: d.design_system_id,
+        seed_systems: false,
+      };
+    } else {
+      const [rulebooks, ds] = await Promise.all([listRulebooks(), fetchDesignSystems()]);
+      alwaysOn.value = rulebooks.filter((r) => r.always_on).map((r) => ({ id: r.id, title: r.title }));
+      others.value = rulebooks.filter((r) => !r.always_on).map((r) => ({ id: r.id, title: r.title }));
+      designSystems.value = ds.design_systems.map((d) => ({ id: d.id, title: d.title }));
+    }
+  } catch (e: unknown) {
+    error.value = apiErrorMessage(e, "Could not load what this project could inherit");
+  } finally {
+    loading.value = false;
+  }
+}
+
+function inherits(id: number): boolean {
+  return !local.value.exclude_always_on_rulebooks.includes(id);
+}
+function toggleInherit(id: number) {
+  const list = local.value.exclude_always_on_rulebooks;
+  local.value.exclude_always_on_rulebooks = list.includes(id) ? list.filter((x) => x !== id) : [...list, id];
+}
+function subscribed(id: number): boolean {
+  return local.value.subscribe_rulebooks.includes(id);
+}
+function toggleSubscribe(id: number) {
+  const list = local.value.subscribe_rulebooks;
+  local.value.subscribe_rulebooks = list.includes(id) ? list.filter((x) => x !== id) : [...list, id];
+}
+
+const nothingToDecide = computed(
+  () => !alwaysOn.value.length && !others.value.length && !designSystems.value.length,
+);
+
+async function record() {
+  if (!props.projectId) return;
+  saving.value = true;
+  error.value = "";
+  try {
+    const decision = await decideInception(props.projectId, local.value);
+    emit("decided", decision);
+  } catch (e: unknown) {
+    error.value = apiErrorMessage(e, "Could not record the decision");
+  } finally {
+    saving.value = false;
+  }
+}
+
+onMounted(load);
+</script>
+
+<template>
+  <section class="inception" aria-labelledby="inception-title">
+    <h3 id="inception-title" class="inception-title">What does this project inherit?</h3>
+    <p class="inception-lede">
+      A project's inheritance is a decision, not a default. Until it is recorded,
+      every always-on rulebook binds, nothing is subscribed, and there is no design
+      system or Systems.
+    </p>
+    <p v-if="loading" class="inception-muted">Loading…</p>
+    <p v-else-if="error" class="error-msg">{{ error }}</p>
+    <template v-else>
+      <div v-if="alwaysOn.length" class="inception-group">
+        <h4>Always-on rulebooks</h4>
+        <p class="inception-muted">Checked = inherits. Uncheck to exclude a rulebook for this project only.</p>
+        <label v-for="rb in alwaysOn" :key="rb.id" class="inception-choice">
+          <input type="checkbox" :checked="inherits(rb.id)" @change="toggleInherit(rb.id)" />
+          <span>{{ rb.title }}</span>
+        </label>
+      </div>
+      <div v-if="others.length" class="inception-group">
+        <h4>Subscribe to rulebooks</h4>
+        <label v-for="rb in others" :key="rb.id" class="inception-choice">
+          <input type="checkbox" :checked="subscribed(rb.id)" @change="toggleSubscribe(rb.id)" />
+          <span>{{ rb.title }}</span>
+        </label>
+      </div>
+      <div class="inception-group">
+        <h4>Design system</h4>
+        <select v-model="local.design_system_id" class="inception-select" aria-label="Design system">
+          <option :value="null">None</option>
+          <option v-for="ds in designSystems" :key="ds.id" :value="ds.id">{{ ds.title }}</option>
+        </select>
+      </div>
+      <div class="inception-group">
+        <label class="inception-choice">
+          <input type="checkbox" v-model="local.seed_systems" :disabled="systemsCount > 0" />
+          <span>
+            Seed the standard starter Systems (CI &amp; Release, Auth &amp; Access, Data Model &amp; Storage, …)
+            <em v-if="systemsCount > 0" class="inception-muted"> — this project already has {{ systemsCount }}</em>
+          </span>
+        </label>
+      </div>
+      <p v-if="nothingToDecide" class="inception-muted">
+        Nothing to inherit yet on this install — recording still settles the question.
+      </p>
+      <div v-if="mode === 'decide'" class="inception-actions">
+        <button class="btn-primary" :disabled="saving" @click="record">
+          {{ saving ? "Recording…" : "Record decision" }}
+        </button>
+      </div>
+    </template>
+  </section>
+</template>
+
+<style scoped>
+.inception {
+  background: var(--fs-surface-raised);
+  border: 1px solid var(--fs-border-color);
+  border-radius: var(--fs-radius-lg);
+  padding: 1.25rem 1.5rem;
+  margin-bottom: 1.5rem;
+}
+.inception-title { margin: 0 0 0.35rem; font-size: 1.05rem; }
+.inception-lede { margin: 0 0 1rem; color: var(--fs-text-secondary); font-size: 0.9rem; }
+.inception-muted { color: var(--fs-text-tertiary); font-size: 0.85rem; margin: 0 0 0.35rem; }
+.inception-group { margin-bottom: 1rem; }
+.inception-group h4 { margin: 0 0 0.35rem; font-size: 0.9rem; font-weight: 500; }
+.inception-choice { display: flex; align-items: flex-start; gap: 0.5rem; font-size: 0.9rem; margin: 0.25rem 0; }
+.inception-choice input { margin-top: 0.2rem; accent-color: var(--fs-accent); }
+.inception-select {
+  padding: 0.45rem 0.7rem;
+  border: 1px solid var(--fs-border-color);
+  border-radius: var(--fs-radius-sm);
+  background: var(--fs-surface-page);
+  color: var(--fs-text-primary);
+  font-size: 0.9rem;
+}
+.inception-actions { display: flex; justify-content: flex-end; margin-top: 0.5rem; }
+.error-msg { color: var(--fs-error); font-size: 0.9rem; }
+</style>

frontend/src/components/rules/ProjectRulesTab.vue

@@ -2,10 +2,18 @@
 import { ref, onMounted, watch } from "vue";
 import { useRouter } from "vue-router";
 import {
-  getProjectApplicableRules, subscribeProject, unsubscribeProject,
+  getProjectApplicableRules,
-  listRulebooks, getRule, createProjectRule, deleteRule,
+  subscribeProject,
-  suppressRuleForProject, unsuppressRuleForProject,
+  unsubscribeProject,
-  suppressTopicForProject, unsuppressTopicForProject,
+  listRulebooks,
+  getRule,
+  createProjectRule,
+  deleteRule,
+  suppressRuleForProject,
+  unsuppressRuleForProject,
+  suppressTopicForProject,
+  unsuppressTopicForProject,
+  includeAlwaysOnRulebook,
 } from "@/api/rulebooks";
 import type { ApplicableRules, Rulebook } from "@/api/rulebooks";
 
@@ -35,6 +43,11 @@ async function subscribe(rulebookId: number) {
   await load();
 }
 
+async function includeBack(rulebookId: number) {
+  await includeAlwaysOnRulebook(props.projectId, rulebookId);
+  await load();
+}
+
 async function unsubscribe(rulebookId: number) {
   if (!confirm("Unsubscribe from this rulebook for this project?")) return;
   await unsubscribeProject(props.projectId, rulebookId);
@@ -172,6 +185,17 @@ watch(() => props.projectId, load);
       </div>
     </section>
 
+    <section v-if="applicable.excluded_always_on?.length" class="excluded">
+      <h3>Excluded always-on rulebooks</h3>
+      <p class="excluded-note">Opted out at inception — these do not bind this project.</p>
+      <div class="chips">
+        <span v-for="rb in applicable.excluded_always_on" :key="rb.id" class="chip chip-excluded">
+          <a @click="openInRulesView(rb.id)">{{ rb.title }}</a>
+          <button class="chip-remove" @click="includeBack(rb.id)" aria-label="Include again" title="Include again">↩</button>
+        </span>
+      </div>
+    </section>
+
     <section class="project-rules">
       <div class="section-head">
         <h3>Project rules</h3>
@@ -321,6 +345,9 @@ watch(() => props.projectId, load);
 </template>
 
 <style scoped>
+.excluded-note { margin: 0 0 0.5rem; color: var(--fs-text-tertiary); font-size: 0.85rem; }
+.chip-excluded { opacity: 0.8; text-decoration: line-through; }
+.chip-excluded .chip-remove { text-decoration: none; }
 .rules-tab { padding: 1rem; }
 h3 {
   font-size: 0.9em; opacity: 0.7; text-transform: uppercase; letter-spacing: 0.05em;

frontend/src/views/ProjectListView.vue

@@ -1,7 +1,9 @@
 <script setup lang="ts">
 import { ref, computed, onMounted } from "vue";
 import { useRouter } from "vue-router";
-import { apiGet, apiPost } from "@/api/client";
+import { apiGet, apiPost, apiErrorMessage } from "@/api/client";
+import { emptyChoices, type InceptionChoices } from "@/api/inception";
+import InceptionCard from "@/components/InceptionCard.vue";
 import { useToastStore } from "@/stores/toast";
 import { milestoneColor } from "@/utils/palette";
 
@@ -47,6 +49,9 @@ const newTitle = ref("");
 const newDescription = ref("");
 const newGoal = ref("");
 const creating = ref(false);
+// Step 2 of the modal (milestone 297): what the new project inherits.
+const modalStep = ref<1 | 2>(1);
+const newInception = ref<InceptionChoices>(emptyChoices());
 
 const filteredProjects = computed(() => {
   if (activeTab.value === "all") return projects.value;
@@ -73,6 +78,8 @@ function openNewProjectModal() {
   newTitle.value = "";
   newDescription.value = "";
   newGoal.value = "";
+  modalStep.value = 1;
+  newInception.value = emptyChoices();
   showNewProjectModal.value = true;
 }
 
@@ -88,13 +95,15 @@ async function createProject() {
       title: newTitle.value.trim(),
       description: newDescription.value.trim() || undefined,
       goal: newGoal.value.trim() || undefined,
+      // The decision rides the create: a project made here is never undecided.
+      inception: newInception.value,
     });
     projects.value.unshift(project);
     showNewProjectModal.value = false;
     toast.show("Project created");
     router.push(`/projects/${project.id}`);
-  } catch {
+  } catch (e: unknown) {
-    toast.show("Failed to create project", "error");
+    toast.show(apiErrorMessage(e, "Failed to create project"), "error");
   } finally {
     creating.value = false;
   }
@@ -266,8 +275,9 @@ function overallPct(project: Project): { total: number; pct: number } {
     <teleport to="body">
       <div v-if="showNewProjectModal" class="modal-overlay" @click.self="closeModal">
         <div class="modal-card">
-          <h3 class="modal-title">New Project</h3>
+          <h3 class="modal-title">{{ modalStep === 1 ? "New Project" : "New Project — what it inherits" }}</h3>
-          <div class="modal-field">
+          <InceptionCard v-if="modalStep === 2" mode="create" v-model:choices="newInception" />
+          <div v-if="modalStep === 1" class="modal-field">
             <label>Title <span class="required">*</span></label>
             <input
               v-model="newTitle"
@@ -275,11 +285,11 @@ function overallPct(project: Project): { total: number; pct: number } {
               class="modal-input"
               placeholder="Project title"
               autofocus
-              @keydown.enter="createProject"
+              @keydown.enter="modalStep = 2"
               @keydown.escape="closeModal"
             />
           </div>
-          <div class="modal-field">
+          <div v-if="modalStep === 1" class="modal-field">
             <label>Goal</label>
             <input
               v-model="newGoal"
@@ -289,7 +299,7 @@ function overallPct(project: Project): { total: number; pct: number } {
               @keydown.escape="closeModal"
             />
           </div>
-          <div class="modal-field">
+          <div v-if="modalStep === 1" class="modal-field">
             <label>Description</label>
             <textarea
               v-model="newDescription"
@@ -301,7 +311,17 @@ function overallPct(project: Project): { total: number; pct: number } {
           </div>
           <div class="modal-actions">
             <button class="modal-btn" @click="closeModal">Cancel</button>
+            <button v-if="modalStep === 2" class="modal-btn" @click="modalStep = 1">Back</button>
             <button
+              v-if="modalStep === 1"
+              class="modal-btn modal-btn-primary"
+              @click="modalStep = 2"
+              :disabled="!newTitle.trim()"
+            >
+              Next
+            </button>
+            <button
+              v-else
               class="modal-btn modal-btn-primary"
               @click="createProject"
               :disabled="!newTitle.trim() || creating"

frontend/src/views/ProjectView.vue

@@ -11,6 +11,9 @@ import ShareDialog from "@/components/ShareDialog.vue";
 import ProjectDesignTab from "@/components/ProjectDesignTab.vue";
 import ProjectRulesTab from "@/components/rules/ProjectRulesTab.vue";
 import SystemsSection from "@/components/SystemsSection.vue";
+import InceptionCard from "@/components/InceptionCard.vue";
+import { fmtDate } from "@/utils/dateFormat";
+import type { InceptionDecision, InceptionRecord } from "@/api/inception";
 import {
   fetchDesignSystems,
   setProjectDesignSystem,
@@ -50,6 +53,7 @@ interface Project {
   color: string | null;
   design_system_id: number | null;
   forge_connection_id: number | null;
+  inception?: InceptionRecord | null;
   permission?: string;
   created_at: string;
   updated_at: string;
@@ -75,6 +79,12 @@ interface NoteItem {
 const route = useRoute();
 const router = useRouter();
 const toast = useToastStore();
+
+function onInceptionDecided(decision: InceptionDecision) {
+  if (project.value) project.value.inception = decision.inception;
+  toast.show("Inheritance recorded");
+  void loadProject();
+}
 const tasksStore = useTasksStore();
 
 const project = ref<Project | null>(null);
@@ -695,6 +705,26 @@ async function confirmDelete() {
         </p>
       </div>
 
+      <!-- Inception (milestone 297): the owner of an undecided project is asked
+           what it inherits; once recorded, one line says what was decided. -->
+      <InceptionCard
+        v-if="project.inception == null && isProjectOwner"
+        mode="decide"
+        :project-id="projectId"
+        @decided="onInceptionDecided"
+      />
+      <p v-else-if="project.inception" class="inception-line">
+        Inheritance decided {{ fmtDate(project.inception.decided_at) }} via {{ project.inception.via }}
+        <template v-if="project.inception.choices.exclude_always_on_rulebooks.length">
+          · excludes {{ project.inception.choices.exclude_always_on_rulebooks.length }} always-on rulebook(s)
+        </template>
+        <template v-if="project.inception.choices.subscribe_rulebooks.length">
+          · subscribes {{ project.inception.choices.subscribe_rulebooks.length }}
+        </template>
+        · design system {{ project.inception.choices.design_system_id ? "#" + project.inception.choices.design_system_id : "none" }}
+        <template v-if="project.inception.choices.seed_systems"> · Systems seeded</template>
+      </p>
+
       <!-- Summary stat chips -->
       <div v-if="project.summary" class="summary-stats">
         <div class="stat-chip stat-todo">
@@ -1197,6 +1227,7 @@ async function confirmDelete() {
   min-width: 200px;
 }
 
+.inception-line { margin: 0 0 1rem; color: var(--fs-text-secondary); font-size: 0.85rem; }
 .project-title-input {
   flex: 1;
   font-size: 1.75rem;

plugin/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "scribe",
   "description": "Scribe system-of-record for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, process-skills (writing-plans, systematic-debugging, verification, brainstorming, reusing-code), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
-  "version": "0.1.37",
+  "version": "0.1.39",
   "author": { "name": "Bryan Van Deusen" },
   "mcpServers": {
     "scribe": {

plugin/README.md

@@ -52,8 +52,18 @@ On install you'll be asked for:
   but never stop it; silent when nothing is recorded, which is most of the time.
   Two framings: a REUSE menu (similar/nearby records), and a SYNC nudge when a
   snippet records the exact file being edited — "updating the record is part of
-  the edit" — each with its own once-per-session dedup.
+  the edit" — each with its own once-per-session dedup. A third, ledger-fed
+  line names a duplicate family (no canon) or a canon recorded elsewhere for
+  the names being written (its own dedup channel, `exclude_derive`).
   Toggle in **Settings → Knowledge auto-inject**.
+- `hooks/hooks.json` → PostToolUse hook on `Bash`
+  (`hooks/scribe_after_write.sh`): code written through sed/heredocs/scripts
+  never reaches the PreToolUse hook, so this one diffs the working tree after
+  every Bash call (per-session path+blob snapshot; one `git status` when
+  nothing changed) and runs the same arms on the definitions just written,
+  through the same endpoint and the same dedup channels. `additionalContext`
+  only; silent on any failure. The extractor, the prose/data skip list and the
+  local by-name duplicate arm are shared in `hooks/scribe_defs.sh`.
 - `skills/` → the universal process-skills, surfaced by description match.
 - `hooks/scribe_sync_processes.sh` (a 2nd SessionStart hook) + the `/scribe:sync`
   command → generate `~/.claude/skills/scribe-proc-*` stubs from your Scribe

plugin/hooks/hooks.json

@@ -34,6 +34,17 @@
           }
         ]
       }
+    ],
+    "PostToolUse": [
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "bash \"${CLAUDE_PLUGIN_ROOT}/hooks/scribe_after_write.sh\""
+          }
+        ]
+      }
     ]
   }
 }

plugin/hooks/scribe_after_write.sh

@@ -0,0 +1,221 @@
+#!/usr/bin/env bash
+# Scribe plugin — PostToolUse write-path trigger on Bash (#2901).
+#
+# scribe_prior_art.sh fires before a Write/Edit TOOL CALL. Code written any
+# other way — sed, heredocs, python edit scripts, `cat > file` — never reached
+# it, so a whole class of edits (the ones a long session makes most) got no
+# prior-art hint, no ledger feed and no duplicate-family warning. This hook
+# closes that: after EVERY Bash call it asks git what changed in the working
+# tree since it last looked, and runs the same arms on the definitions that
+# were just written — the local by-name duplicate arm, the recorded prior-art
+# arms and the ledger's derive/divergence checks (#2900/#2793), via the same
+# /api/plugin/prior-art endpoint the pre-write hook uses.
+#
+# Post-hoc by a few seconds, in the same moment and the same session: "the
+# copy just landed; here is its family" — not "an audit found it later".
+#
+# Cheap when nothing changed: one `git status`. State per session, beside the
+# pre-write hook's (its three dedup channels are SHARED, so a family named by
+# one hook is not named again by the other):
+#   ${TMPDIR:-/tmp}/scribe-afterwrite/<sid>.snap   path<TAB>blob-hash of every
+#                                                  dirty/untracked file last seen
+#   ${TMPDIR:-/tmp}/scribe-priorart/<sid>.*        the dedup channels
+#
+# NEVER BLOCKS. It returns `additionalContext` only (no decision — there is
+# nothing left to decide, the write already happened). Any failure —
+# unconfigured, unreachable, not a git repo, malformed — exits 0 in silence.
+#
+# Config (same as the other hooks):
+#   CLAUDE_PLUGIN_OPTION_API_ENDPOINT  base URL, no trailing slash
+#   CLAUDE_PLUGIN_OPTION_API_TOKEN     fmcp_ API key (sensitive)
+#   SCRIBE_URL / SCRIBE_TOKEN override for the settings.json dogfooding path.
+set -uo pipefail
+
+command -v jq  >/dev/null 2>&1 || exit 0
+command -v git >/dev/null 2>&1 || exit 0
+
+# shellcheck source=plugin/hooks/scribe_defs.sh
+. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"
+
+# PostToolUse delivers { session_id, cwd, tool_name, tool_input, tool_response }.
+event=$(cat 2>/dev/null || true)
+tool_name=$(printf '%s' "$event" | jq -r '.tool_name // empty' 2>/dev/null) || exit 0
+[ "$tool_name" = "Bash" ] || exit 0
+session_id=$(printf '%s' "$event" | jq -r '.session_id // empty' 2>/dev/null) || session_id=""
+event_cwd=$(printf '%s' "$event" | jq -r '.cwd // empty' 2>/dev/null) || event_cwd=""
+work_dir=${event_cwd:-${CLAUDE_PROJECT_DIR:-$PWD}}
+repo_root=$(git -C "$work_dir" rev-parse --show-toplevel 2>/dev/null) || exit 0
+[ -n "$repo_root" ] || exit 0
+
+safe_sid=$(printf '%s' "${session_id:-nosession}" | tr -c 'A-Za-z0-9._-' '_')
+snap_dir="${TMPDIR:-/tmp}/scribe-afterwrite"
+mkdir -p "$snap_dir" 2>/dev/null || true
+snap="$snap_dir/${safe_sid}.snap"
+
+# What is dirty now: every modified / added / untracked path, with the blob
+# hash of its working-tree content. Hash, not mtime: portable (no stat
+# flags), exact (a touch is not a change), and untracked files hash the same
+# way tracked ones do.
+current=""
+while IFS= read -r line; do
+  [ -n "$line" ] || continue
+  status=${line:0:2}
+  path=${line:3}
+  case "$status" in
+    D*|*D) continue ;;                       # a deletion defines nothing
+  esac
+  case "$path" in
+    *" -> "*) path=${path##* -> } ;;          # rename: the new name
+  esac
+  # Porcelain quotes paths with special characters; those are skipped rather
+  # than unquoted badly — a filename needing quotes is not where shapes live.
+  case "$path" in
+    \"*) continue ;;
+  esac
+  [ -f "$repo_root/$path" ] || continue
+  sha=$(git -C "$repo_root" hash-object -- "$path" 2>/dev/null) || continue
+  current="${current}${path}"$'\t'"${sha}"$'\n'
+done < <(git -C "$repo_root" status --porcelain --untracked-files=all 2>/dev/null)
+
+previous=""
+[ -f "$snap" ] && previous=$(cat "$snap" 2>/dev/null || true)
+first_run=0
+[ -f "$snap" ] || first_run=1
+# Write the new snapshot NOW, before anything can fail below — the next call
+# must compare against this tree, whatever happens to this one's hint.
+printf '%s' "$current" > "$snap" 2>/dev/null || true
+
+# Changed = a (path, hash) pair not in the previous snapshot. On the very
+# first call of a session there is no previous snapshot; rather than report
+# every pre-existing dirty file as "just written", take only files touched in
+# the last minute — the Bash call that just ran is the likely author.
+changed=""
+while IFS=$'\t' read -r path sha; do
+  [ -n "${path:-}" ] || continue
+  if [ "$first_run" = 1 ]; then
+    [ -n "$(find "$repo_root/$path" -mmin -1 2>/dev/null)" ] || continue
+  else
+    case "$previous" in
+      *"${path}"$'\t'"${sha}"*) continue ;;
+    esac
+  fi
+  scribe_skip_path "$path" && continue
+  changed="${changed}${path}"$'\n'
+done <<< "$current"
+[ -n "$changed" ] || exit 0
+
+url=${SCRIBE_URL:-${CLAUDE_PLUGIN_OPTION_API_ENDPOINT:-}}
+token=${SCRIBE_TOKEN:-${CLAUDE_PLUGIN_OPTION_API_TOKEN:-}}
+case "$url"   in *'${'*) url="" ;;  esac
+case "$token" in *'${'*) token="" ;; esac
+repo=$(git -C "$repo_root" remote get-url origin 2>/dev/null || true)
+repo_q=""
+if [ -n "$repo" ]; then
+  enc=$(printf '%s' "$repo" | jq -sRr '@uri' 2>/dev/null) || enc=""
+  [ -n "$enc" ] && repo_q="&repo=${enc}"
+fi
+
+# The dedup channels are the PRE-write hook's files, on purpose (see header).
+state_dir="${TMPDIR:-/tmp}/scribe-priorart"
+mkdir -p "$state_dir" 2>/dev/null || true
+idfile="$state_dir/${safe_sid}.ids"
+syncfile="$state_dir/${safe_sid}.sync.ids"
+derivefile="$state_dir/${safe_sid}.derive.ids"
+
+combined=""
+n_files=0
+while IFS= read -r rel_path; do
+  [ -n "${rel_path:-}" ] || continue
+  # A Bash call that rewrote many files is a refactor or a generator, not a
+  # shape being instantiated; four is enough to name what matters.
+  n_files=$((n_files + 1))
+  [ "$n_files" -le 4 ] || break
+  file_path="$repo_root/$rel_path"
+
+  # The code just written: the ADDED lines of the uncommitted diff for a
+  # tracked file (sed, not cut: this strips one marker char per line, it is
+  # not a payload cap), the whole file when untracked.
+  if git -C "$repo_root" ls-files --error-unmatch -- "$rel_path" >/dev/null 2>&1; then
+    code=$(git -C "$repo_root" diff -U0 -- "$rel_path" 2>/dev/null | grep '^+' | grep -v '^+++' | sed 's/^+//') || code=""
+  else
+    code=$(cat "$file_path" 2>/dev/null) || code=""
+  fi
+  [ -n "$code" ] || continue
+  names=$(printf '%s' "$code" | scribe_defs | sort -u | head -12) || names=""
+  # Nothing DEFINED in what was written (prose, data, a call-site edit) →
+  # nothing to say; the arms are about shapes.
+  [ -n "$names" ] || continue
+
+  local_lines=$(scribe_local_dups "$repo_root" "$rel_path" <<< "$names") || local_lines=""
+  local_context=""
+  if [ -n "$local_lines" ]; then
+    local_context="> Already defined elsewhere in this repo — \`${rel_path}\` (just written) adds another copy; check before keeping it (\`git grep\` shown; a nudge, not a gate):"$'\n'"${local_lines}"
+  fi
+
+  context=""
+  body=""
+  if [ -n "$url" ] && [ -n "$token" ]; then
+    q=$(printf '%s' "$code" | head -c 1200)
+    path_enc=$(printf '%s' "$rel_path" | jq -sRr '@uri' 2>/dev/null) || path_enc=""
+    code_enc=$(printf '%s' "$q" | jq -sRr '@uri' 2>/dev/null) || code_enc=""
+    shapes_q=""
+    enc=$(printf '%s\n' "$names" \
+      | awk -F'\t' 'NF>=2 {printf "%s%s:%s", (n++?",":""), $1, $2}' \
+      | jq -sRr '@uri' 2>/dev/null) || enc=""
+    [ -n "$enc" ] && shapes_q="&shapes=${enc}"
+    exclude_q=""; sync_exclude_q=""; derive_exclude_q=""
+    if [ -f "$idfile" ]; then
+      seen=$(tr '\n' ',' < "$idfile" 2>/dev/null | sed 's/,$//')
+      [ -n "$seen" ] && exclude_q="&exclude_ids=${seen}"
+    fi
+    if [ -f "$syncfile" ]; then
+      sync_seen=$(tr '\n' ',' < "$syncfile" 2>/dev/null | sed 's/,$//')
+      [ -n "$sync_seen" ] && sync_exclude_q="&exclude_sync_ids=${sync_seen}"
+    fi
+    if [ -f "$derivefile" ]; then
+      derive_seen=$(tr '\n' ',' < "$derivefile" 2>/dev/null | sed 's/,$//' | jq -sRr '@uri' 2>/dev/null) || derive_seen=""
+      [ -n "$derive_seen" ] && derive_exclude_q="&exclude_derive=${derive_seen}"
+    fi
+    if [ -n "$path_enc" ]; then
+      body=$(curl -fsS --max-time 4 \
+        -H "Authorization: Bearer ${token}" \
+        "${url%/}/api/plugin/prior-art?path=${path_enc}&code=${code_enc}${repo_q}${exclude_q}${sync_exclude_q}${derive_exclude_q}${shapes_q}" 2>/dev/null) || body=""
+    fi
+    if [ -n "$body" ]; then
+      context=$(printf '%s' "$body" | jq -r '.context // empty' 2>/dev/null) || context=""
+      if [ -n "$context" ]; then
+        printf '%s' "$body" | jq -r '((.note_ids // []) - (.sync_note_ids // []))[]?' 2>/dev/null >> "$idfile" || true
+        printf '%s' "$body" | jq -r '(.sync_note_ids // [])[]?' 2>/dev/null >> "$syncfile" || true
+        printf '%s' "$body" | jq -r '(.derive_keys // [])[]?' 2>/dev/null >> "$derivefile" || true
+        # Several files in one call may name the same family: keep each
+        # token once, so the next request's exclude list stays exact.
+        for f in "$idfile" "$syncfile" "$derivefile"; do
+          [ -s "$f" ] && { sort -u -o "$f" "$f" 2>/dev/null || true; }
+        done
+      fi
+    fi
+  fi
+
+  # The record nudge (#2664), same gate as the pre-write hook: duplication
+  # demonstrated locally AND nothing recorded for it.
+  if [ -n "$local_lines" ]; then
+    n_recorded=$(printf '%s' "$body" | jq -r '.note_ids | length' 2>/dev/null) || n_recorded=0
+    if [ "${n_recorded:-0}" = "0" ] || [ "$n_recorded" = "" ]; then
+      local_context="${local_context}"$'\n'"> None of those existing copies is recorded in Scribe. If the version just written is the canonical one — or this edit is consolidating the copies — record it now with create_snippet so the next session is offered it instead of writing another copy."
+    fi
+  fi
+
+  part="$local_context"
+  if [ -n "$context" ]; then
+    [ -n "$part" ] && part="${part}"$'\n'
+    part="${part}${context}"
+  fi
+  [ -n "$part" ] || continue
+  [ -n "$combined" ] && combined="${combined}"$'\n'
+  combined="${combined}${part}"
+done <<< "$changed"
+
+[ -n "$combined" ] || exit 0
+jq -n --arg c "$combined" \
+  '{hookSpecificOutput: {hookEventName: "PostToolUse", additionalContext: $c}}'
+exit 0

plugin/hooks/scribe_defs.sh

@@ -0,0 +1,109 @@
+#!/usr/bin/env bash
+# shellcheck shell=bash
+# Scribe plugin — the pieces the two write-path hooks share (#2901).
+#
+# scribe_prior_art.sh fires BEFORE a Write/Edit tool call; scribe_after_write.sh
+# fires AFTER a Bash tool call and diffs the working tree, so code written by
+# sed/heredocs/scripts gets the same prior-art and ledger checks. Both need the
+# same three things, kept here so they cannot drift apart:
+#
+#   scribe_skip_path PATH      formats that hold prose or data, not shapes
+#   scribe_defs                stdin code → "kind<TAB>name" per definition
+#   scribe_local_dups ROOT REL "kind<TAB>name" lines on stdin → the by-name
+#                              local-duplicate lines (ARM 1, #2280)
+#
+# Sourced, not executed: `. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"`.
+
+# Skip formats that hold prose or data rather than reusable code. Purely to
+# avoid a pointless round-trip — the server would return nothing for these
+# anyway. Config formats are NOT skipped: a CI workflow or a compose file is
+# often exactly the thing worth reusing.
+scribe_skip_path() {
+  case "$1" in
+    *.md|*.mdx|*.txt|*.rst|*.json|*.lock|*.log|*.csv|*.tsv|*.svg|*.png|*.jpg|*.jpeg|*.gif|*.ico|*.pdf)
+      return 0 ;;
+  esac
+  return 1
+}
+
+# ---------------------------------------------------------------------------
+# kind<TAB>name for each thing a piece of code DEFINES, in source order. One
+# program, two consumers: the local duplicate arm (every definition in the
+# payload) and the ledger feed (#2791, below: the definitions being written,
+# or the one enclosing an Edit). Rule-for-rule mirrored by the server's
+# services/coverage.py extract_shapes — ledger rows are keyed by what THAT
+# sees, so the two must agree on what counts as a definition.
+scribe_defs() {
+  awk '
+    {
+      # CSS class definition: .name { or .name,
+      if (match($0, /^[[:space:]]*\.[A-Za-z][A-Za-z0-9_-]*[[:space:]]*[,{]/)) {
+        t = $0; sub(/^[[:space:]]*\./, "", t); sub(/[[:space:]]*[,{].*$/, "", t)
+        if (t != "") print "css\t" t; next
+      }
+      line = $0; sub(/^[[:space:]]+/, "", line)
+      # Strip leading declaration modifiers so the definition keyword is the
+      # first word regardless of language (export/pub/private/suspend/...).
+      sub(/^((pub(\([a-z]+\))?|export|default|private|internal|protected|public|static|suspend|async|open|sealed|data|abstract|final|inline|unsafe|extern|override)[[:space:]]+)*/, "", line)
+      # Go method with receiver: func (r *T) Name(
+      if (match(line, /^func[[:space:]]*\([^)]*\)[[:space:]]*[A-Za-z_]/)) {
+        t = line; sub(/^func[[:space:]]*\([^)]*\)[[:space:]]*/, "", t)
+        sub(/[^A-Za-z0-9_].*$/, "", t)
+        if (t != "") print "sym\t" t; next
+      }
+      # Keyword-announced definitions, functions and named types alike.
+      # Dunders are skipped: every class defines __init__, so "already defined
+      # in N other files" is guaranteed noise for them — and noise is what
+      # teaches sessions to skip the hint.
+      if (match(line, /^(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+[A-Za-z_$]/)) {
+        t = line; sub(/^[a-z]+[[:space:]]+/, "", t)
+        sub(/[^A-Za-z0-9_$].*$/, "", t)
+        if (t != "" && t !~ /^__.*__$/) print "sym\t" t; next
+      }
+      # Arrow/expression assignment: const name = (…) / let name = async (
+      if (match(line, /^(const|let)[[:space:]]+[A-Za-z_$][A-Za-z0-9_$]*[[:space:]]*=[[:space:]]*(async[[:space:]]*)?[(<]/)) {
+        t = line; sub(/^(const|let)[[:space:]]+/, "", t)
+        sub(/[^A-Za-z0-9_$].*$/, "", t)
+        if (t != "") print "sym\t" t; next
+      }
+    }
+  ' 2>/dev/null
+}
+
+
+# ---------------------------------------------------------------------------
+# ARM 1 — BY NAME, LOCALLY (#2280). Does a definition of this already exist?
+#
+# The recorded arms ask Scribe what was RECORDED; the ledger arm (#2900) asks
+# what a BOUND repo's ledger knows. A helper nobody recorded, in a repo nobody
+# bound, is invisible to both — which is how `.btn-primary` came to be defined
+# four times, already diverged. This arm asks the one question only the
+# developer's machine can answer, inside the repo, holding the code about to
+# be written: no index, no storage, no server — it runs even on an install
+# that has never configured Scribe.
+#
+# Definition-shaped patterns only. Grepping for bare occurrences would match
+# every CALL site and drown the real finding — and a hint that is mostly noise
+# is one people learn to skip, which is worse than none. ALL code, not a
+# language shortlist (#2682): the same keyword family scribe_defs announces.
+#
+# $1 repo root, $2 repo-relative path of the file being written (excluded from
+# the grep — it would always match itself on an Edit). Definitions on stdin.
+# Prints one "> - `name` is already defined in N other file(s): …" per hit.
+scribe_local_dups() {
+  local root="$1" rel="$2" kind name pat hits count label files
+  while IFS=$'\t' read -r kind name; do
+    [ -n "${name:-}" ] || continue
+    case "$kind" in
+      css) pat="^[[:space:]]*\.${name}[[:space:]]*[,{]" ;;
+      *)   pat="(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+${name}[^A-Za-z0-9_]|func[[:space:]]*\([^)]*\)[[:space:]]*${name}[[:space:]]*\(|(const|let)[[:space:]]+${name}[[:space:]]*=" ;;
+    esac
+    # -I skips binaries; :(exclude) drops the file being written.
+    hits=$(git -C "$root" grep -I -l -E -e "$pat" -- . ":(exclude)${rel}" 2>/dev/null | head -4) || hits=""
+    [ -n "$hits" ] || continue
+    count=$(printf '%s\n' "$hits" | grep -c . 2>/dev/null || echo 0)
+    label=$([ "$kind" = css ] && printf '.%s' "$name" || printf '%s' "$name")
+    files=$(printf '%s' "$hits" | tr '\n' ' ' | sed 's/ $//')
+    printf '> - `%s` is already defined in %s other file(s): %s\n' "$label" "$count" "$files"
+  done
+}

plugin/hooks/scribe_prior_art.sh

@@ -51,14 +51,12 @@ code=$(printf '%s' "$event" | jq -r '
   .tool_input.content // .tool_input.file_content //
   .tool_input.new_string // .tool_input.new_str // empty' 2>/dev/null) || code=""
 
-# Skip formats that hold prose or data rather than reusable code. Purely to
+# Shared with the after-write hook (#2901): the prose/data skip list, the
-# avoid a pointless round-trip — the server would return nothing for these
+# definition extractor and the local by-name duplicate arm live in
-# anyway. Config formats are NOT skipped: a CI workflow or a compose file is
+# scribe_defs.sh so the two hooks cannot drift apart.
-# often exactly the thing worth reusing.
+# shellcheck source=plugin/hooks/scribe_defs.sh
-case "$file_path" in
+. "$(dirname "${BASH_SOURCE[0]}")/scribe_defs.sh"
-  *.md|*.mdx|*.txt|*.rst|*.json|*.lock|*.log|*.csv|*.tsv|*.svg|*.png|*.jpg|*.jpeg|*.gif|*.ico|*.pdf)
+scribe_skip_path "$file_path" && exit 0
-    exit 0 ;;
-esac
 
 # Snippet locations are recorded repo-relative, so send a repo-relative path —
 # an absolute one would simply match nothing. Resolved BEFORE the config gate
@@ -73,78 +71,8 @@ if [ -n "$repo_root" ]; then
   esac
 fi
 
-# ---------------------------------------------------------------------------
+# ARM 1 — BY NAME, LOCALLY (#2280): does a definition of this already exist
-# ARM 1 — BY NAME, LOCALLY (#2280). Does a definition of this already exist?
+# in the repo? (scribe_local_dups in scribe_defs.sh carries the why.)
-#
-# The other two arms ask Scribe what was RECORDED. Scribe has never read a line
-# of the codebase, so a helper nobody thought to record is invisible to them —
-# which is how `.btn-primary` came to be defined four times, in four scoped
-# stylesheets, already diverged. It was never a snippet, so no threshold and no
-# query rewrite could ever have surfaced it.
-#
-# This arm closes that by asking the only question the record cannot answer,
-# in the only place that can: the hook already runs on the developer's machine,
-# inside the repo, holding the code about to be written. No index, no storage,
-# no staleness, and no server — it deliberately runs even on an install that
-# has never configured Scribe.
-#
-# Definition-shaped patterns only. Grepping for bare occurrences would match
-# every CALL site and drown the real finding — and a hint that is mostly noise
-# is one people learn to skip, which is worse than none.
-#
-# ALL code, not a language shortlist (#2682): the detector was born covering
-# only the languages of the repo it was written in, which silently amputated
-# this whole arm — and the record nudge gated on it — for every Go/Kotlin/Rust
-# project. Definitions are announced by a small keyword family across
-# languages (func/fun/fn/function/def/sub · class/struct/trait/interface/
-# enum/object/protocol/type), so one modifier-strip + keyword match covers
-# them all. Known out of scope: keyword-less declaration syntax (C/Java/Dart
-# `ReturnType name(...)`) needs a real parser, and `impl` blocks are excluded
-# because several per type is normal Rust, not duplication.
-# ---------------------------------------------------------------------------
-# kind<TAB>name for each thing a piece of code DEFINES, in source order. One
-# program, two consumers: the local duplicate arm (every definition in the
-# payload) and the ledger feed (#2791, below: the definitions being written,
-# or the one enclosing an Edit). Rule-for-rule mirrored by the server's
-# services/coverage.py extract_shapes — ledger rows are keyed by what THAT
-# sees, so the two must agree on what counts as a definition.
-scribe_defs() {
-  awk '
-    {
-      # CSS class definition: .name { or .name,
-      if (match($0, /^[[:space:]]*\.[A-Za-z][A-Za-z0-9_-]*[[:space:]]*[,{]/)) {
-        t = $0; sub(/^[[:space:]]*\./, "", t); sub(/[[:space:]]*[,{].*$/, "", t)
-        if (t != "") print "css\t" t; next
-      }
-      line = $0; sub(/^[[:space:]]+/, "", line)
-      # Strip leading declaration modifiers so the definition keyword is the
-      # first word regardless of language (export/pub/private/suspend/...).
-      sub(/^((pub(\([a-z]+\))?|export|default|private|internal|protected|public|static|suspend|async|open|sealed|data|abstract|final|inline|unsafe|extern|override)[[:space:]]+)*/, "", line)
-      # Go method with receiver: func (r *T) Name(
-      if (match(line, /^func[[:space:]]*\([^)]*\)[[:space:]]*[A-Za-z_]/)) {
-        t = line; sub(/^func[[:space:]]*\([^)]*\)[[:space:]]*/, "", t)
-        sub(/[^A-Za-z0-9_].*$/, "", t)
-        if (t != "") print "sym\t" t; next
-      }
-      # Keyword-announced definitions, functions and named types alike.
-      # Dunders are skipped: every class defines __init__, so "already defined
-      # in N other files" is guaranteed noise for them — and noise is what
-      # teaches sessions to skip the hint.
-      if (match(line, /^(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+[A-Za-z_$]/)) {
-        t = line; sub(/^[a-z]+[[:space:]]+/, "", t)
-        sub(/[^A-Za-z0-9_$].*$/, "", t)
-        if (t != "" && t !~ /^__.*__$/) print "sym\t" t; next
-      }
-      # Arrow/expression assignment: const name = (…) / let name = async (
-      if (match(line, /^(const|let)[[:space:]]+[A-Za-z_$][A-Za-z0-9_$]*[[:space:]]*=[[:space:]]*(async[[:space:]]*)?[(<]/)) {
-        t = line; sub(/^(const|let)[[:space:]]+/, "", t)
-        sub(/[^A-Za-z0-9_$].*$/, "", t)
-        if (t != "") print "sym\t" t; next
-      }
-    }
-  ' 2>/dev/null
-}
-
 names=""
 if [ -n "$code" ]; then
   names=$(printf '%s' "$code" | scribe_defs | sort -u | head -12) || names=""
@@ -152,21 +80,8 @@ fi
 
 local_lines=""
 if [ -n "$repo_root" ] && [ -n "$names" ]; then
-  while IFS=$'\t' read -r kind name; do
+  local_lines=$(scribe_local_dups "$repo_root" "$rel_path" <<< "$names") || local_lines=""
-    [ -n "${name:-}" ] || continue
+  [ -n "$local_lines" ] && local_lines="${local_lines}"$'\n'
-    case "$kind" in
-      css) pat="^[[:space:]]*\.${name}[[:space:]]*[,{]" ;;
-      *)   pat="(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+${name}[^A-Za-z0-9_]|func[[:space:]]*\([^)]*\)[[:space:]]*${name}[[:space:]]*\(|(const|let)[[:space:]]+${name}[[:space:]]*=" ;;
-    esac
-    # -I skips binaries; :(exclude) drops the file being written, which would
-    # otherwise always match itself on an Edit.
-    hits=$(git -C "$repo_root" grep -I -l -E -e "$pat" -- . ":(exclude)${rel_path}" 2>/dev/null | head -4) || hits=""
-    [ -n "$hits" ] || continue
-    count=$(printf '%s\n' "$hits" | grep -c . 2>/dev/null || echo 0)
-    label=$([ "$kind" = css ] && printf '.%s' "$name" || printf '%s' "$name")
-    files=$(printf '%s' "$hits" | tr '\n' ' ' | sed 's/ $//')
-    local_lines="${local_lines}> - \`${label}\` is already defined in ${count} other file(s): ${files}"$'\n'
-  done <<< "$names"
 fi
 
 local_context=""
@@ -258,14 +173,22 @@ fi
 # the sync nudge when the recorded file itself is edited later.
 state_dir="${TMPDIR:-/tmp}/scribe-priorart"
 mkdir -p "$state_dir" 2>/dev/null || true
+#
+# A THIRD channel (#2900): the ledger's derive arm names a duplicate family
+# (a derive group id) or a canon elsewhere (`canon:<snippet_id>`) for the
+# shapes being written. Keyed by that token, not a note id, so it dedups on
+# its own file and a family is named once per session, not at every edit.
 idfile=""
 syncfile=""
+derivefile=""
 exclude_q=""
 sync_exclude_q=""
+derive_exclude_q=""
 if [ -n "$session_id" ]; then
   safe_sid=$(printf '%s' "$session_id" | tr -c 'A-Za-z0-9._-' '_')
   idfile="$state_dir/${safe_sid}.ids"
   syncfile="$state_dir/${safe_sid}.sync.ids"
+  derivefile="$state_dir/${safe_sid}.derive.ids"
   if [ -f "$idfile" ]; then
     seen=$(tr '\n' ',' < "$idfile" 2>/dev/null | sed 's/,$//')
     [ -n "$seen" ] && exclude_q="&exclude_ids=${seen}"
@@ -274,13 +197,17 @@ if [ -n "$session_id" ]; then
     sync_seen=$(tr '\n' ',' < "$syncfile" 2>/dev/null | sed 's/,$//')
     [ -n "$sync_seen" ] && sync_exclude_q="&exclude_sync_ids=${sync_seen}"
   fi
+  if [ -f "$derivefile" ]; then
+    derive_seen=$(tr '\n' ',' < "$derivefile" 2>/dev/null | sed 's/,$//' | jq -sRr '@uri' 2>/dev/null) || derive_seen=""
+    [ -n "$derive_seen" ] && derive_exclude_q="&exclude_derive=${derive_seen}"
+  fi
 fi
 
 # `|| true`, not `|| exit 0`: an unreachable instance must not discard a local
 # finding that needed no instance to produce.
 body=$(curl -fsS --max-time 5 \
   -H "Authorization: Bearer ${token}" \
-  "${url%/}/api/plugin/prior-art?path=${path_enc}&code=${code_enc}${repo_q}${exclude_q}${sync_exclude_q}${shapes_q}" 2>/dev/null) || body=""
+  "${url%/}/api/plugin/prior-art?path=${path_enc}&code=${code_enc}${repo_q}${exclude_q}${sync_exclude_q}${derive_exclude_q}${shapes_q}" 2>/dev/null) || body=""
 
 context=""
 if [ -n "$body" ]; then
@@ -295,6 +222,9 @@ if [ -n "$body" ]; then
     if [ -n "$syncfile" ]; then
       printf '%s' "$body" | jq -r '(.sync_note_ids // [])[]?' 2>/dev/null >> "$syncfile" || true
     fi
+    if [ -n "$derivefile" ]; then
+      printf '%s' "$body" | jq -r '(.derive_keys // [])[]?' 2>/dev/null >> "$derivefile" || true
+    fi
   fi
 fi
 

plugin/hooks/scribe_static_context.md

@@ -66,7 +66,10 @@ for the operator's work, and as your own working memory across sessions.
   should read as a map of every shape in it. The backstop still holds:
   noticing the second copy of anything, or consolidating copies into a shared
   X, means X gets recorded before that work is finished — which is how a
-  codebase is kept from growing four `.btn-primary` definitions.
+  codebase is kept from growing four `.btn-primary` definitions. The write-path
+  hooks (before a Write/Edit, and after any Bash call that changed the tree)
+  name a known duplicate family or a canon elsewhere for what was just
+  written — act on that line at the write, not at the next audit.
 - Do **not** keep the operator's rules, plans, or project notes in local
   memory / CLAUDE.md in parallel with Scribe — Scribe holds the single copy.
 - **Compact at clean seams** — because you record as you go, a context

plugin/skills/reusing-code/SKILL.md

@@ -44,6 +44,13 @@ through recall/auto-inject; this skill is the active reflex around that.
   it before you go any further. Either it's the helper you were about to
   duplicate — reuse it and drop yours — or it isn't, and the record needs the new
   location adding. Both are cheaper now than after the duplicate settles in.
+- **A `Shape ledger at …` line is the ledger speaking, not the record.** It
+  names a duplicate family ("identical body in N other files, no canon") or a
+  canon elsewhere for a name you just wrote — for edits made through Bash
+  (sed, heredocs, scripts) as much as through Write/Edit. Derive the family or
+  reuse the canon *now*; a family that is convention rather than copies is
+  dismissed with `classify_shapes(..., status="exempt",
+  reason_code="convention-plumbing")`, never ignored.
 - **A `[records this file]` hint is a duty, not a menu.** When the hint says a
   snippet records the very file you're editing, the record's freshness is now
   YOUR edit's responsibility: if the edit changes the recorded shape,

plugin/skills/shape-accounting/SKILL.md

@@ -85,6 +85,34 @@ the dominant form, `create_snippet` it, migrate the outliers, then classify
 the rest as instances. Canon is determined from the code; consistency comes
 from the derivation, not from asking permission.
 
+## Derive groups are drift, not audit material
+
+The catalogue exists so the codebase is DRY **from inception**, not as DRY as
+the last sweep left it. Three surfaces say so without anyone running an audit
+(milestone 299):
+
+- **At the write** — the prior-art hint (the Write/Edit hook, and since
+  0.1.39 the after-write hook on Bash, so sed/heredoc/script edits count too)
+  carries a `Shape ledger at <path>` line when a name just written is a known
+  **duplicate family** ("identical body in N other files, no canon") or a
+  **canon elsewhere** ("snippet #N at <path> — reuse, don't redefine"). Act
+  on it *then*: pull the canon and build from it, or derive the family now —
+  `create_snippet` the dominant form, repoint the copies, `classify_shapes`
+  them `instance`. A family is named once per session.
+- **On arrival** — the coverage line's `standing:` block (shown even when
+  nothing is unclassified) and `derive_new` ("+N new copies since last
+  refresh: .x in <path>") name what drifted since the previous refresh. That
+  is the todo of the moment, sized to the last batch — not a backlog.
+- **A family that is convention, not copies** — component-local `load` /
+  `toggle` / `save` that happen to share a name — is dismissed, not
+  consolidated: `classify_shapes(..., status="exempt",
+  reason_code="convention-plumbing", reason=…)` (or `classify_shapes_by_rule`
+  for a whole family) removes it from the queue. Dismissal is a judgment and
+  it is recorded; silence is not.
+
+After the one-time pay-down the derive queue reads empty; anything in it
+afterwards is drift of the moment, and the hint already said so at the write.
+
 ## The divergence readout — button B where button A is canon
 
 Three questions the ledger answers mechanically (#2793):

plugin/skills/using-scribe/SKILL.md

@@ -120,6 +120,28 @@ bound — confine the session to it:
 - If something clearly belongs to a *different* project, say so and **ask before
   switching** — never silently operate cross-project.
 
+## Starting a project: decide what it inherits
+
+A project's inheritance is a **decision, not a default**. Before
+`create_project`, ask the operator the four inception questions and pass the
+answers — never create a project bare by default:
+
+- which **always-on rulebooks** it should NOT inherit (`list_rulebooks` shows
+  which are always_on; default: inherit them all) →
+  `exclude_always_on_rulebooks=[...]`
+- which other rulebooks to **subscribe** → `subscribe_rulebooks=[...]`
+- which **design system** its UI is built from (`list_design_systems`; or
+  none) → `design_system_id=<id | -1>`
+- whether to **seed the standard starter Systems** so records can be tagged
+  from day one → `seed_systems=true|false`
+
+If `enter_project` returns an `inception` key, the project was never decided
+(it inherits its defaults silently): raise that ask once, with the defaults it
+carries, then `decide_project_inception(project_id, …)`. Existing projects
+were stamped "legacy" (inherit-all) and do not ask; any project can be
+re-decided. The rules/design-system/Systems tools still work one at a time —
+inception is the moment they are decided together, and the record of why.
+
 ## Where a new rule goes
 
 When codifying a rule, pick its home by **who it should bind** — and keep

scripts/check_plugin.py

@@ -203,6 +203,17 @@ SMOKE_EVENTS: dict[str, str] = {
     ),
     "scribe_sync_processes.sh": json.dumps({"source": "startup"}),
     "scribe_session_context.sh": json.dumps({"source": "startup"}),
+    # The after-write hook (#2901) diffs the working tree; on CI's clean
+    # checkout there is nothing to report, so silence is the right assertion.
+    # (On a dirty local tree with a definition just written it may speak —
+    # that is the hook working, not a failure of the contract.)
+    "scribe_after_write.sh": json.dumps(
+        {"session_id": "smoke", "cwd": ".", "tool_name": "Bash",
+         "tool_input": {"command": "true"}, "tool_response": {}}
+    ),
+    # The shared library is sourced, never run; executed bare it defines
+    # functions and exits — silent by construction.
+    "scribe_defs.sh": "",
 }
 
 # The one hook that legitimately produces output with no credentials.

src/scribe/mcp/server.py

@@ -37,24 +37,23 @@ in local files (CLAUDE.md, auto-memory); Scribe holds the single copy.
 
 Hierarchy: Project -> Milestone -> Task/Note. The map, by purpose:
 - ORIENT: enter_project(id) at session start — rules, open tasks, recent
-  notes, Systems and design system in one call.
+  notes, Systems, design system. `inception` key: ask what the project
+  inherits, decide_project_inception (create_project takes the same).
 - DO: create_task. Fixed a problem? kind="issue" (symptom -> root cause ->
   fix), never a work-log line on an unrelated task. Log with add_task_log;
   keep status honest — in_progress on start, done on finish.
 - PLAN work with an arc: start_planning. The plan IS a milestone; each step is
   a child task, not a checkbox. No local plan .md files.
-- CAPTURE: create_note. RECALL: search first, before answering about the
+- CAPTURE: create_note. RECALL: search first — prior art exists; pass the
-  operator's work or opening a task — assume prior art exists, and pass the
   active project_id to stay in scope.
 - WHERE work happens: Systems. Tag records with system_ids as you write;
   create_system when the area is unmodelled.
-- HOW to work: rules are pull-only and binding — call list_always_on_rules()
+- HOW: rules are binding — list_always_on_rules() at session start.
-  yourself at session start.
 - UI: the project's design system is binding — resolve_design_system /
   get_design_system_stylesheet before hand-writing a value.
 - REUSE: search snippets before writing a helper; record what you build with
   create_snippet; classify shapes against canon (classify_shapes) — a
-  consumer map is rows, never prose. Saved procedures are Processes (follow
+  consumer map is rows, never prose. Processes are saved procedures (follow
   verbatim). Deletes are trash-recoverable.
 
 A task is a note with status (*_note vs *_task tools).

src/scribe/mcp/tools/projects.py

@@ -20,6 +20,7 @@ from scribe.mcp._context import current_user_id
 from scribe.mcp.tools import systems as systems_tools
 from scribe.services import coverage as coverage_svc
 from scribe.services import design_systems as design_systems_svc
+from scribe.services import inception as inception_svc
 from scribe.services import milestones as milestones_svc
 from scribe.services import notes as notes_svc
 from scribe.services import projects as projects_svc
@@ -80,6 +81,12 @@ async def enter_project(project_id: int) -> dict:
     create it with create_system rather than leaving the area unmodelled. Read
     a subsystem's accumulated records with list_system_records.
 
+    `inception` (milestone 297) appears ONLY when the project is yours and
+    nobody has decided what it inherits: it carries the current defaults
+    (which always-on rulebooks bind, design system, Systems), what to ask the
+    operator — once — and the decide_project_inception call that answers it;
+    it repeats on every enter until a decision is recorded.
+
     `systems_bootstrap` appears ONLY when the project has many records and no
     Systems at all — act on it before starting other work: create_system a
     starter vocabulary from the areas the project's records name, directly
@@ -141,6 +148,14 @@ async def enter_project(project_id: int) -> dict:
             uid, project_id
         )
 
+    # The inception ask (milestone 297): a project nobody has decided on
+    # inherits its defaults silently — always-on rulebooks, no design system,
+    # no Systems. Owner-only (deciding is the owner's), and only until a
+    # decision is recorded; the key is ABSENT otherwise (#2483).
+    inception_ask = None
+    if project.user_id == uid and not inception_svc.is_decided(project):
+        inception_ask = await inception_svc.inception_ask(uid, project_id)
+
     # Probably the largest surfacing by volume, and it emitted nothing — so
     # the pulls it caused floated unattributed and the surfaced:pulled ratio
     # ran against a denominator missing its biggest contributor (#2477). An
@@ -213,6 +228,8 @@ async def enter_project(project_id: int) -> dict:
     # readers to skip it (#2483), and this one exists to be acted on.
     if systems_bootstrap:
         out["systems_bootstrap"] = systems_bootstrap
+    if inception_ask:
+        out["inception"] = inception_ask
     return out
 
 
@@ -238,14 +255,43 @@ async def get_project(project_id: int) -> dict:
     return data
 
 
+def _inception_choices(
+    exclude_always_on_rulebooks, subscribe_rulebooks, design_system_id, seed_systems,
+) -> dict | None:
+    """The tool args → an inception choices object, or None when no inception
+    arg was given at all (a bare create stays undecided and enter_project
+    asks). design_system_id: 0 = not stated, -1 = explicitly none, n = that
+    system."""
+    if (exclude_always_on_rulebooks is None and subscribe_rulebooks is None
+            and not design_system_id and seed_systems is None):
+        return None
+    return {
+        "exclude_always_on_rulebooks": list(exclude_always_on_rulebooks or []),
+        "subscribe_rulebooks": list(subscribe_rulebooks or []),
+        "design_system_id": None if design_system_id in (0, -1) else design_system_id,
+        "seed_systems": bool(seed_systems),
+    }
+
+
 async def create_project(
     title: str,
     description: str = "",
     goal: str = "",
     status: str = "active",
     color: str = "",
+    exclude_always_on_rulebooks: list[int] | None = None,
+    subscribe_rulebooks: list[int] | None = None,
+    design_system_id: int = 0,
+    seed_systems: bool | None = None,
 ) -> dict:
-    """Create a new project in Scribe.
+    """Create a new project in Scribe — and decide what it inherits.
+
+    A project's inheritance is a decision, not a default (milestone 297):
+    before calling, ask the operator the four inception questions and pass
+    the answers; a project created without any of them is UNDECIDED and
+    enter_project will ask until decide_project_inception records it.
+    Defaults if nobody decides: every always-on rulebook binds, nothing is
+    subscribed, no design system, no Systems.
 
     Args:
         title: Project name (required).
@@ -253,6 +299,14 @@ async def create_project(
         goal: The desired outcome or definition of done for the project.
         status: one of active (default), paused, completed, archived.
         color: Optional hex colour for the project card (e.g. "#6366f1").
+        exclude_always_on_rulebooks: always-on rulebook ids this project does
+            NOT inherit ([] = inherit them all). list_rulebooks shows which are
+            always_on.
+        subscribe_rulebooks: rulebook ids to subscribe (the non-always-on ones).
+        design_system_id: the design system this project's UI is built from
+            (list_design_systems); -1 = explicitly none; 0 = not stated.
+        seed_systems: true mints the standard starter Systems (CI & Release,
+            Auth & Access, …) so records can be tagged from day one.
     """
     uid = current_user_id()
     project = await projects_svc.create_project(
@@ -263,7 +317,52 @@ async def create_project(
         status=status,
         color=color or None,
     )
-    return project.to_dict()
+    data = project.to_dict()
+    choices = _inception_choices(
+        exclude_always_on_rulebooks, subscribe_rulebooks, design_system_id, seed_systems,
+    )
+    if choices is not None:
+        decided = await inception_svc.decide(uid, project.id, choices=choices, via="mcp")
+        data["inception"] = decided["inception"]
+        data["inception_effects"] = decided["effects"]
+    else:
+        data["inception_hint"] = (
+            "Undecided: this project inherits its defaults until "
+            "decide_project_inception records what it should inherit "
+            "(enter_project will ask)."
+        )
+    return data
+
+
+async def decide_project_inception(
+    project_id: int,
+    exclude_always_on_rulebooks: list[int] | None = None,
+    subscribe_rulebooks: list[int] | None = None,
+    design_system_id: int = 0,
+    seed_systems: bool | None = None,
+) -> dict:
+    """Record what a project inherits — answer enter_project's `inception` ask,
+    or re-decide later (milestone 297).
+
+    Owner-only. Applies the effects through the ordinary tools' paths —
+    exclude_always_on_rulebook, subscribe_project_to_rulebook,
+    set_project_design_system, the standard Systems seed — and writes the
+    decision on the project last, so get_project/enter_project can say why
+    the project has the rules, design and Systems it has. Re-deciding is
+    additive for exclusions/subscriptions (use include_always_on_rulebook /
+    unsubscribe_project_from_rulebook to undo one), replaces the design
+    system, and never re-seeds Systems a project already has.
+
+    Args: as create_project's inception args. Passing nothing records an
+    inherit-all decision (every always-on rulebook binds, no subscriptions,
+    no design system, no seed) — a valid answer, stated.
+    """
+    uid = current_user_id()
+    choices = _inception_choices(
+        exclude_always_on_rulebooks, subscribe_rulebooks, design_system_id, seed_systems,
+    ) or {}
+    decided = await inception_svc.decide(uid, project_id, choices=choices, via="mcp")
+    return {"project_id": project_id, **decided}
 
 
 async def update_project(
@@ -320,6 +419,6 @@ def register(mcp) -> None:
         get_project,
         create_project,
         update_project,
-        delete_project,
+        delete_project, decide_project_inception,
     ):
         mcp.tool(name=fn.__name__)(fn)

src/scribe/mcp/tools/rulebooks.py

@@ -222,16 +222,22 @@ async def list_rules(
     return {"rules": [_rule_summary(r) for r in rows], "total": len(rows)}
 
 
-async def list_always_on_rules() -> dict:
+async def list_always_on_rules(project_id: int = 0) -> dict:
     """Return all rules from rulebooks flagged always_on for the current user.
 
     Call this at session start. Treat the returned rules as binding for the
     session — they apply regardless of which project (if any) is in scope.
     Pair with get_project(id).applicable_rules when working on a specific
     project to also load that project's subscription-derived rules.
+
+    Args:
+        project_id: 0 (default) = the user-wide set. Inside a project, pass
+            its id: an always-on rulebook the project EXCLUDED at inception
+            (see enter_project's `excluded_always_on`) is left out — the
+            project decided not to inherit it.
     """
     uid = current_user_id()
-    rules = await rulebooks_svc.list_always_on_rules(uid)
+    rules = await rulebooks_svc.list_always_on_rules(uid, project_id=project_id)
     return {"rules": [_rule_summary(r) for r in rules], "total": len(rules)}
 
 
@@ -407,6 +413,35 @@ async def unsubscribe_project_from_rulebook(
 
 # ── Suppressions — project-level mute of rulebook rules / topics ────────
 
+async def exclude_always_on_rulebook(project_id: int, rulebook_id: int) -> dict:
+    """Opt a project OUT of a whole always-on rulebook (milestone 297).
+
+    Always-on rulebooks bind every project implicitly; an inception decision
+    can say "not this one, not here". The exclusion is total for that project
+    — list_always_on_rules(project_id), enter_project/get_project rules and
+    the session-start context all leave it out and name it under
+    `excluded_always_on`. Owner-only; the rulebook must be always_on (a
+    subscribed rulebook is left with unsubscribe_project_from_rulebook).
+    Idempotent; include_always_on_rulebook reverses it. Normally reached via
+    decide_project_inception, not by hand.
+    """
+    uid = current_user_id()
+    await rulebooks_svc.exclude_always_on_rulebook_for_project(
+        project_id=project_id, rulebook_id=rulebook_id, user_id=uid,
+    )
+    return {"project_id": project_id, "rulebook_id": rulebook_id, "excluded": True}
+
+
+async def include_always_on_rulebook(project_id: int, rulebook_id: int) -> dict:
+    """Reverse exclude_always_on_rulebook: the always-on rulebook binds this
+    project again. Idempotent."""
+    uid = current_user_id()
+    await rulebooks_svc.include_always_on_rulebook_for_project(
+        project_id=project_id, rulebook_id=rulebook_id, user_id=uid,
+    )
+    return {"project_id": project_id, "rulebook_id": rulebook_id, "excluded": False}
+
+
 async def suppress_rule_for_project(
     project_id: int, rule_id: int,
 ) -> dict:
@@ -470,5 +505,6 @@ def register(mcp) -> None:
         subscribe_project_to_rulebook, unsubscribe_project_from_rulebook,
         suppress_rule_for_project, unsuppress_rule_for_project,
         suppress_topic_for_project, unsuppress_topic_for_project,
+        exclude_always_on_rulebook, include_always_on_rulebook,
     ):
         mcp.tool(name=fn.__name__)(fn)

src/scribe/mcp/tools/shapes.py

@@ -295,7 +295,9 @@ async def refresh_pattern_coverage(project_id: int) -> dict:
     Returns the accounting payload — total, accounted, counts by status,
     unclassified, repos, largest_gaps, `proposed` (canon proposals awaiting
     confirmation), `derive_groups` (the biggest repeats-with-no-canon
-    families), `proposer` (what this refresh examined) — plus
+    families), `derive_new` (copies that joined a family since the previous
+    refresh — the drift to act on now: derive the canon, don't queue an
+    audit), `proposer` (what this refresh examined) — plus
     `pattern_coverage`, the same one-line summary enter_project carries.
     """
     uid = current_user_id()

src/scribe/mcp/tools/systems.py

@@ -30,10 +30,10 @@ _BOOTSTRAP_TITLES = 6
 # design (rule #115): archetypes any codebase could have, never one
 # install's subsystems. Mint freely beyond the list; the duplicate gate
 # guards sprawl.
-_STANDARD_SYSTEMS = (
+# The standard vocabulary lives with the service (services/systems.
-    "CI & Release", "Auth & Access", "Data Model & Storage", "API Surface",
+# STANDARD_SYSTEMS) since milestone 297 — the inception seed mints it and this
-    "UI & Design", "Import & Export", "Background Jobs", "Observability",
+# ask names it, one list for both.
-)
+_STANDARD_SYSTEMS = tuple(name for name, _charter in systems_svc.STANDARD_SYSTEMS)
 
 
 async def bootstrap_systems_ask(user_id: int, project_id: int) -> str | None:

src/scribe/models/project.py

@@ -1,5 +1,6 @@
 import enum
 from sqlalchemy import BigInteger, ForeignKey, Integer, Text
+from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import Mapped, mapped_column
 from scribe.models import Base
 from scribe.models.base import SoftDeleteMixin, TimestampMixin, iso
@@ -36,6 +37,14 @@ class Project(Base, TimestampMixin, SoftDeleteMixin):
         BigInteger, ForeignKey("forge_connections.id", ondelete="SET NULL"),
         nullable=True,
     )
+    # The inception record (milestone 297): what this project was decided to
+    # inherit, when, and through which door — {decided_at, decided_by, via,
+    # choices: {exclude_always_on_rulebooks, subscribe_rulebooks,
+    # design_system_id, seed_systems}}. NULL means nobody has decided yet,
+    # and enter_project asks; the effects themselves live in the subscription
+    # / exclusion tables, design_system_id and the project's Systems — this is
+    # the WHY, kept so later surfaces can say it. See services/inception.py.
+    inception: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
 
     def to_dict(self) -> dict:
         return {
@@ -48,6 +57,7 @@ class Project(Base, TimestampMixin, SoftDeleteMixin):
             "color": self.color,
             "design_system_id": self.design_system_id,
             "forge_connection_id": self.forge_connection_id,
+            "inception": self.inception,
             "created_at": iso(self.created_at),
             "updated_at": iso(self.updated_at),
         }

src/scribe/models/rulebook.py

@@ -129,6 +129,19 @@ project_rule_suppressions = Table(
     Column("created_at", DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)),
 )
 
+# A project's opt-out of a whole ALWAYS-ON rulebook (milestone 297): the
+# sibling of the two suppression tables below, one level up. Always-on
+# rulebooks bind every project implicitly; an inception decision can exclude
+# specific ones for this project, and get_applicable_rules /
+# list_always_on_rules(project_id) skip them. FKs CASCADE like the others.
+project_rulebook_exclusions = Table(
+    "project_rulebook_exclusions",
+    Base.metadata,
+    Column("project_id", BigInteger, ForeignKey("projects.id", ondelete="CASCADE"), primary_key=True),
+    Column("rulebook_id", BigInteger, ForeignKey("rulebooks.id", ondelete="CASCADE"), primary_key=True),
+    Column("created_at", DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)),
+)
+
 project_topic_suppressions = Table(
     "project_topic_suppressions",
     Base.metadata,

src/scribe/routes/plugin.py

@@ -129,6 +129,10 @@ async def write_path_prior_art():
                              surfaced. A separate channel on purpose: a reuse
                              hint shown early must not suppress the record-sync
                              nudge when the recorded file is edited later.
+        exclude_derive (opt) — comma-separated derive keys (a derive group id
+                             or `canon:<snippet_id>`) already named this
+                             session by the ledger arm (#2900); its own
+                             channel, like the two above.
         shapes (opt)       — comma-separated `kind:name` definitions the hook
                              found in (or enclosing) the payload, kind being
                              css|sym. The shape ledger's write-path feed
@@ -144,6 +148,9 @@ async def write_path_prior_art():
     project_id, repo, _unbound = await _project_scope()
     exclude_ids = _int_list(request.args.get("exclude_ids"))
     exclude_sync_ids = _int_list(request.args.get("exclude_sync_ids"))
+    exclude_derive = [
+        p.strip() for p in (request.args.get("exclude_derive") or "").split(",") if p.strip()
+    ]
     shapes = _parse_shapes(request.args.get("shapes") or "")
     api_key = getattr(g, "api_key", None)
     may_stamp = api_key is None or getattr(api_key, "scope", "") == "write"
@@ -153,6 +160,7 @@ async def write_path_prior_art():
         exclude_ids=exclude_ids, exclude_sync_ids=exclude_sync_ids,
         stamp_shapes=shapes if may_stamp else None,
         repo_key=repo_bindings_svc.normalize_repo_key(repo) if repo else "",
+        exclude_derive=exclude_derive,
     )
     return jsonify(result)
 

src/scribe/routes/projects.py

@@ -5,6 +5,7 @@ from quart import Blueprint, g, jsonify, request
 
 from scribe.auth import login_required, get_current_user_id
 from scribe.routes.utils import not_found, parse_pagination
+from scribe.services import inception as inception_svc
 from scribe.services.milestones import list_milestones
 from scribe.services.notes import list_notes
 from scribe.services.projects import (
@@ -66,6 +67,15 @@ async def create_project_route():
     status = data.get("status", "active")
     if status not in ("active", "paused", "completed", "archived"):
         return jsonify({"error": "status must be 'active', 'paused', 'completed', or 'archived'"}), 400
+    # The inception decision rides the create (milestone 297): the UI's
+    # second step sends `inception: {choices}`; absent = undecided, and the
+    # project page shows the card until it is. Validated before the create
+    # so a bad decision never leaves a half-made project behind.
+    inception = data.get("inception")
+    if inception is not None:
+        error = inception_svc.validate_inception(inception)
+        if error:
+            return jsonify({"error": error}), 400
     project = await create_project(
         uid,
         title=data["title"],
@@ -74,7 +84,44 @@ async def create_project_route():
         color=data.get("color"),
         status=status,
     )
-    return jsonify(project.to_dict()), 201
+    out = project.to_dict()
+    if inception is not None:
+        try:
+            decided = await inception_svc.decide(uid, project.id, choices=inception, via="ui")
+        except ValueError as exc:
+            return jsonify({"error": str(exc), "project": out}), 400
+        out["inception"] = decided["inception"]
+        out["inception_effects"] = decided["effects"]
+    return jsonify(out), 201
+
+
+@projects_bp.route("/<int:project_id>/inception", methods=["POST"])
+@login_required
+async def decide_inception_route(project_id: int):
+    """Record (or re-record) what a project inherits — milestone 297.
+    Body: the choices object {exclude_always_on_rulebooks, subscribe_rulebooks,
+    design_system_id, seed_systems}; owner-only."""
+    uid = get_current_user_id()
+    data = await request.get_json() or {}
+    choices = data.get("choices", data)
+    try:
+        decided = await inception_svc.decide(uid, project_id, choices=choices, via="ui")
+    except ValueError as exc:
+        msg = str(exc)
+        status = 404 if "not found" in msg else 400
+        return jsonify({"error": msg}), status
+    return jsonify({"project_id": project_id, **decided})
+
+
+@projects_bp.route("/<int:project_id>/inception/defaults", methods=["GET"])
+@login_required
+async def inception_defaults_route(project_id: int):
+    """What the project inherits if nobody decides — the card's payload."""
+    uid = get_current_user_id()
+    try:
+        return jsonify(await inception_svc.current_defaults(uid, project_id))
+    except ValueError:
+        return not_found("Project")
 
 
 @projects_bp.route("/<int:project_id>", methods=["GET"])

src/scribe/routes/rulebooks.py

@@ -288,6 +288,32 @@ async def unsuppress_project_topic(project_id: int, topic_id: int):
     return "", 204
 
 
+@rulebooks_bp.post("/projects/<int:project_id>/exclusions/rulebooks/<int:rulebook_id>")
+@login_required
+async def exclude_project_rulebook(project_id: int, rulebook_id: int):
+    """Opt the project out of a whole always-on rulebook (milestone 297)."""
+    try:
+        await rulebooks_svc.exclude_always_on_rulebook_for_project(
+            project_id=project_id, rulebook_id=rulebook_id, user_id=get_current_user_id(),
+        )
+    except ValueError as exc:
+        msg = str(exc)
+        return jsonify({"error": msg}), (400 if "not always-on" in msg else 404)
+    return "", 204
+
+
+@rulebooks_bp.delete("/projects/<int:project_id>/exclusions/rulebooks/<int:rulebook_id>")
+@login_required
+async def include_project_rulebook(project_id: int, rulebook_id: int):
+    try:
+        await rulebooks_svc.include_always_on_rulebook_for_project(
+            project_id=project_id, rulebook_id=rulebook_id, user_id=get_current_user_id(),
+        )
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 404
+    return "", 204
+
+
 @rulebooks_bp.post("/projects/<int:project_id>/rules")
 @login_required
 async def create_project_rule(project_id: int):

src/scribe/services/backup.py

@@ -19,6 +19,7 @@ from scribe.models.rulebook import (
     Rulebook,
     RulebookTopic,
     project_rule_suppressions,
+    project_rulebook_exclusions,
     project_rulebook_subscriptions,
     project_topic_suppressions,
 )
@@ -45,8 +46,10 @@ logger = logging.getLogger(__name__)
 # v9 (2026-08) added code_shape_uses — the ledger's consumption edges (#2870):
 # judgment-grade edges (agent/audit/import) are operator records; mechanical
 # ones (reference/hook) travel too, cheaply, and the next refresh refreshes them.
+# v10 (2026-08) added projects.inception + project_rulebook_exclusions
+# (milestone 297): the WHY a project inherits what it does, and its opt-outs.
 # Bump when the serialized schema changes.
-BACKUP_VERSION = 9
+BACKUP_VERSION = 10
 
 # Every table this backup carries, by its REAL name. Paired with _NOT_INCLUDED
 # below, these two lists must together account for the entire schema — which is
@@ -60,7 +63,7 @@ _BACKED_UP = [
     "users", "projects", "milestones", "notes", "task_logs", "note_drafts",
     "note_versions", "settings", "rulebooks", "rulebook_topics", "rules",
     "project_rulebook_subscriptions", "project_rule_suppressions",
-    "project_topic_suppressions",
+    "project_topic_suppressions", "project_rulebook_exclusions",
     # v5 (2026-08): the five-year gap this list was written to stop.
     "systems", "record_systems", "design_systems", "design_tokens",
     "note_usage_events", "repo_bindings", "note_supersessions",
@@ -112,6 +115,10 @@ def _topic_suppression_rows(rows) -> list[dict]:
     return [{"project_id": r.project_id, "topic_id": r.topic_id} for r in rows]
 
 
+def _rulebook_exclusion_rows(rows) -> list[dict]:
+    return [{"project_id": r.project_id, "rulebook_id": r.rulebook_id} for r in rows]
+
+
 # The v5 sections. Pure row-builders like the join-table helpers above, for the
 # same reason: CI has no database, so a serialiser that is a plain function is
 # one that can actually be tested.
@@ -219,6 +226,8 @@ def _project_rows(rows) -> list[dict]:
             "id": p.id, "user_id": p.user_id, "title": p.title,
             "description": p.description, "goal": p.goal, "status": p.status,
             "color": p.color,
+            "design_system_id": p.design_system_id,
+            "inception": p.inception,
             "created_at": p.created_at.isoformat(),
             "updated_at": p.updated_at.isoformat(),
         }
@@ -383,6 +392,9 @@ async def export_full_backup() -> dict:
         topic_suppressions = (await session.execute(
             select(project_topic_suppressions)
         )).all()
+        rulebook_exclusions = (await session.execute(
+            select(project_rulebook_exclusions)
+        )).all()
 
     return {
         "version": BACKUP_VERSION,
@@ -407,6 +419,7 @@ async def export_full_backup() -> dict:
         "rulebook_subscriptions": _subscription_rows(subscriptions),
         "rule_suppressions": _rule_suppression_rows(rule_suppressions),
         "topic_suppressions": _topic_suppression_rows(topic_suppressions),
+        "rulebook_exclusions": _rulebook_exclusion_rows(rulebook_exclusions),
         "systems": _system_rows(systems),
         "record_systems": _record_system_rows(record_systems),
         "design_systems": _design_system_rows(design_systems),
@@ -532,8 +545,13 @@ async def export_user_backup(user_id: int) -> dict:
                     project_topic_suppressions.c.project_id.in_(project_ids)
                 )
             )).all()
+            rulebook_exclusions = (await session.execute(
+                select(project_rulebook_exclusions).where(
+                    project_rulebook_exclusions.c.project_id.in_(project_ids)
+                )
+            )).all()
         else:
-            subscriptions = rule_suppressions = topic_suppressions = []
+            subscriptions = rule_suppressions = topic_suppressions = rulebook_exclusions = []
 
     return {
         "version": BACKUP_VERSION,
@@ -560,6 +578,7 @@ async def export_user_backup(user_id: int) -> dict:
         "rulebook_subscriptions": _subscription_rows(subscriptions),
         "rule_suppressions": _rule_suppression_rows(rule_suppressions),
         "topic_suppressions": _topic_suppression_rows(topic_suppressions),
+        "rulebook_exclusions": _rulebook_exclusion_rows(rulebook_exclusions),
         "systems": _system_rows(systems),
         "record_systems": _record_system_rows(record_systems),
         "design_systems": _design_system_rows(design_systems),
@@ -670,7 +689,7 @@ async def _restore_v2(data: dict) -> dict:
         "task_logs": 0, "note_drafts": 0, "note_versions": 0,
         "settings": 0, "rulebooks": 0, "rulebook_topics": 0, "rules": 0,
         "rulebook_subscriptions": 0, "rule_suppressions": 0,
-        "topic_suppressions": 0,
+        "topic_suppressions": 0, "rulebook_exclusions": 0,
         "systems": 0, "record_systems": 0, "design_systems": 0,
         "design_tokens": 0, "note_usage_events": 0, "repo_bindings": 0,
         "note_supersessions": 0, "code_shapes": 0, "code_shape_events": 0,
@@ -933,6 +952,17 @@ async def _restore_v2(data: dict) -> dict:
             ))
             stats["topic_suppressions"] += 1
 
+        # 14b. Always-on rulebook exclusions (v10, milestone 297)
+        for exc in data.get("rulebook_exclusions", []):
+            mapped_pid = project_id_map.get(exc.get("project_id", 0))
+            mapped_rbid = rulebook_id_map.get(exc.get("rulebook_id", 0))
+            if mapped_pid is None or mapped_rbid is None:
+                continue
+            await session.execute(project_rulebook_exclusions.insert().values(
+                project_id=mapped_pid, rulebook_id=mapped_rbid,
+            ))
+            stats["rulebook_exclusions"] += 1
+
         # --- v5 sections. Every one is data.get()-guarded, so a v2/v3/v4
         # payload restores without them rather than failing on an absent key.
 
@@ -1137,6 +1167,35 @@ async def _restore_v2(data: dict) -> dict:
             ))
             stats["code_shape_uses"] += 1
 
+        # v10: a project's design-system pointer and its inception record ride
+        # the project but point at design systems and rulebooks restored AFTER
+        # it — so they are written last, with ids re-mapped. An id that did
+        # not survive drops out of the record rather than dangling.
+        for p_data in data.get("projects", []):
+            new_pid = project_id_map.get(p_data.get("id") or 0)
+            if new_pid is None:
+                continue
+            proj = await session.get(Project, new_pid)
+            if proj is None:
+                continue
+            old_ds = p_data.get("design_system_id")
+            if old_ds:
+                proj.design_system_id = design_system_id_map.get(old_ds)
+            inception = p_data.get("inception")
+            if isinstance(inception, dict):
+                choices = dict(inception.get("choices") or {})
+                choices["exclude_always_on_rulebooks"] = [
+                    rulebook_id_map[i] for i in choices.get("exclude_always_on_rulebooks") or []
+                    if i in rulebook_id_map
+                ]
+                choices["subscribe_rulebooks"] = [
+                    rulebook_id_map[i] for i in choices.get("subscribe_rulebooks") or []
+                    if i in rulebook_id_map
+                ]
+                ds = choices.get("design_system_id")
+                choices["design_system_id"] = design_system_id_map.get(ds) if ds else None
+                proj.inception = {**inception, "choices": choices}
+
         await session.commit()
 
     logger.info("Restored v2/v3 backup: %s", stats)

src/scribe/services/coverage.py

@@ -191,7 +191,19 @@ def extract_definitions(text: str) -> list[Definition]:
         # same rule under another name?" — .closed-msg / .error-block /
         # .success-msg with identical bodies are one dup group, not three
         # lonely rows. Sym blocks keep their signature line in the hash.
-        hashed = block[1:] if kind == "css" and len(block) > 1 else block
+        if kind == "css":
+            # One-line rules (`.x { color: red; }`) carry their declarations on
+            # the selector line itself; a block that is only the selector plus
+            # trailing blanks must not hash to the empty string (which grouped
+            # 68 unrelated one-liners as one "copy" on first deploy, #2872).
+            first = lines[i]
+            brace = first.find("{")
+            head = [first[brace + 1:]] if brace >= 0 and first[brace + 1:].strip() else []
+            hashed = head + block[1:]
+            if not any(x.strip() for x in hashed):
+                hashed = block
+        else:
+            hashed = block
         out.append(Definition(
             kind, name, lines[i].strip()[:_SIGNATURE_CAP], _block_sha(hashed),
             "\n".join(block), i,
@@ -450,15 +462,20 @@ async def compute_coverage(
         await shape_ledger.apply_derive_groups(project_id)
     except Exception:
         logger.warning("derive-first grouping failed", exc_info=True)
-    # The button-B pass (#2793): shapes new since the PREVIOUS computation,
+    # "Since the previous computation" — the cache's stamp. A first seed has
-    # where a canon dominates. The previous computation's stamp is the cache;
+    # none, so nothing is new then. Read once; two passes use it: the
-    # a first seed has none, so it flags nothing (everything is new then).
+    # button-B flag (#2793) and the derive-new drift count (#2899).
+    since = None
     try:
         previous = await get_setting(user_id, f"{_CACHE_KEY_PREFIX}{project_id}")
-        since = None
         if previous:
             stamp = (json.loads(previous) or {}).get("computed_at")
             since = datetime.fromisoformat(stamp) if stamp else None
+    except Exception:
+        logger.warning("previous coverage stamp unreadable", exc_info=True)
+    # The button-B pass (#2793): shapes new since the PREVIOUS computation,
+    # where a canon dominates.
+    try:
         await shape_ledger.flag_divergence(project_id, since=since)
     except Exception:
         logger.warning("divergence pass failed", exc_info=True)
@@ -479,6 +496,7 @@ async def compute_coverage(
     unclassified = counts.pop("unclassified")
     proposals = shape_ledger.proposal_summary(rows)
     divergence = shape_ledger.divergence_summary(rows)
+    derive_new = shape_ledger.derive_new_summary(rows, since=since)
     return {
         "total": len(rows),
         "accounted": len(rows) - unclassified,
@@ -489,6 +507,10 @@ async def compute_coverage(
         "proposed": proposals["proposed"],
         "derive_groups": proposals["derive_groups"],
         "top_canon": proposals.get("top_canon"),
+        # Drift since the previous refresh (#2899): copies that joined a
+        # duplicate family — what the arrival line names so drift is noticed
+        # on entering, not found by an audit.
+        "derive_new": derive_new,
         "proposer": proposer_stats,
         # The divergence readout (#2793): button B where button A is canon,
         # and judged shapes whose bodies moved since they were judged.
@@ -636,29 +658,46 @@ def coverage_line(coverage: dict) -> str:
         line += f" — {breakdown}"
     line += f" (estimate{', computed ' + day if day else ''})"
     unclassified = coverage.get("unclassified", 0)
+    # The standing work, built whatever the todo count (#2899). Since the
+    # scoped bucket (#2869) a ledger can read 100% accounted and still carry
+    # derive groups, proposals and divergence; gating this block on
+    # `unclassified > 0` is how 439 derive rows went unmentioned.
+    standing = []
+    if coverage.get("proposed"):
+        standing.append(f"{coverage['proposed']} proposed")
+    n_groups = len(coverage.get("derive_groups") or [])
+    if n_groups:
+        standing.append(f"{n_groups} derive group{'s' if n_groups != 1 else ''}")
+    # Drift since the previous refresh: copies that joined a family, the
+    # first one named — the sentence the arrival moment exists to say.
+    new = coverage.get("derive_new") or {}
+    if new.get("count"):
+        n = new["count"]
+        first_new = (new.get("examples") or [{}])[0]
+        where = (
+            f": {first_new['label']} in {first_new['path']}"
+            if first_new.get("label") and first_new.get("path") else ""
+        )
+        standing.append(f"+{n} new cop{'y' if n == 1 else 'ies'} since last refresh{where}")
+    if coverage.get("divergent"):
+        standing.append(f"{coverage['divergent']} DIVERGENT")
+    # The next action, on the line (#2874): the canon with the biggest
+    # queue to confirm, and the widest body-identical copy to consolidate.
+    top = coverage.get("top_canon") or {}
+    if top.get("snippet_id"):
+        standing.append(f"top canon #{top['snippet_id']} ×{top.get('count', 0)}")
+    first = (coverage.get("derive_groups") or [{}])[0]
+    if first.get("label") and first.get("files"):
+        standing.append(f"top copy {first['label']} ×{first['files']} files")
     if unclassified:
         line += f"; {unclassified} unclassified"
-        standing = []
-        if coverage.get("proposed"):
-            standing.append(f"{coverage['proposed']} proposed")
-        n_groups = len(coverage.get("derive_groups") or [])
-        if n_groups:
-            standing.append(f"{n_groups} derive group{'s' if n_groups != 1 else ''}")
-        if coverage.get("divergent"):
-            standing.append(f"{coverage['divergent']} DIVERGENT")
-        # The next action, on the line (#2874): the canon with the biggest
-        # queue to confirm, and the widest body-identical copy to consolidate.
-        top = coverage.get("top_canon") or {}
-        if top.get("snippet_id"):
-            standing.append(f"top canon #{top['snippet_id']} ×{top.get('count', 0)}")
-        first = (coverage.get("derive_groups") or [{}])[0]
-        if first.get("label") and first.get("files"):
-            standing.append(f"top copy {first['label']} ×{first['files']} files")
         if standing:
             line += f" ({', '.join(standing)})"
         gaps = [g["dir"] for g in coverage.get("largest_gaps") or []]
         if gaps:
             line += ", largest: " + ", ".join(gaps)
+    elif standing:
+        line += f"; standing: {', '.join(standing)}"
     if coverage.get("recheck"):
         line += f"; {coverage['recheck']} judged shape{'s' if coverage['recheck'] != 1 else ''} changed since judged — recheck"
     return line

src/scribe/services/inception.py

@@ -0,0 +1,272 @@
+"""Project inception — what a project was decided to inherit (milestone 297).
+
+A project's inheritance is a decision, not a default. The record lives on
+``projects.inception``::
+
+    {
+      "decided_at": "<iso>", "decided_by": <user id> | null,
+      "via": "mcp" | "ui" | "legacy",
+      "choices": {
+        "exclude_always_on_rulebooks": [rulebook ids],
+        "subscribe_rulebooks": [rulebook ids],
+        "design_system_id": <id> | null,
+        "seed_systems": bool
+      }
+    }
+
+NULL = undecided → enter_project asks. ``legacy`` is the migration's stamp on
+projects that existed before the step did (inherit-all / no design system /
+no seed), so the ask fires only for projects created after this shipped.
+
+The shape and its validator are pure; ``decide`` composes the existing
+services — always-on exclusions, subscriptions, set_project_design_system,
+the standard Systems seed — checks every target BEFORE touching anything,
+applies the effects (each idempotent), and writes the record LAST, so a
+half-applied decision is re-runnable rather than recorded as done.
+``current_defaults`` is what the enter_project ask shows: what binds today
+if nobody decides.
+"""
+from __future__ import annotations
+
+from datetime import datetime, timezone
+
+from sqlalchemy import select
+
+from scribe.models import async_session
+from scribe.models.project import Project
+from scribe.models.rulebook import Rulebook
+
+INCEPTION_VIAS = ("mcp", "ui", "legacy")
+CHOICE_KEYS = ("exclude_always_on_rulebooks", "subscribe_rulebooks", "design_system_id", "seed_systems")
+
+
+def _is_id_list(value) -> bool:
+    return isinstance(value, list) and all(
+        isinstance(v, int) and not isinstance(v, bool) and v > 0 for v in value
+    )
+
+
+def validate_inception(choices) -> str | None:
+    """The structural error an inception ``choices`` object would earn, or
+    None. Pure and checked BEFORE any effect is applied: a decision either
+    applies whole or errors whole (the StrictArgs lesson, #2709).
+
+    Accepts the four keys, each optional: two id lists (positive ints, no
+    duplicates between exclude and subscribe), ``design_system_id`` an int
+    or None, ``seed_systems`` a bool. Unknown keys are an error — a typo
+    must not become a silently ignored choice."""
+    if not isinstance(choices, dict):
+        return "choices must be an object"
+    unknown = sorted(set(choices) - set(CHOICE_KEYS))
+    if unknown:
+        return f"unknown inception choice(s): {', '.join(unknown)} (one of: {', '.join(CHOICE_KEYS)})"
+    excl = choices.get("exclude_always_on_rulebooks") or []
+    subs = choices.get("subscribe_rulebooks") or []
+    if not _is_id_list(excl):
+        return "exclude_always_on_rulebooks must be a list of rulebook ids"
+    if not _is_id_list(subs):
+        return "subscribe_rulebooks must be a list of rulebook ids"
+    both = sorted(set(excl) & set(subs))
+    if both:
+        return f"rulebook(s) {both} cannot be both excluded and subscribed"
+    ds = choices.get("design_system_id")
+    if ds is not None and (isinstance(ds, bool) or not isinstance(ds, int) or ds <= 0):
+        return "design_system_id must be a positive id or null"
+    seed = choices.get("seed_systems", False)
+    if not isinstance(seed, bool):
+        return "seed_systems must be true or false"
+    return None
+
+
+def normalize_choices(choices: dict | None) -> dict:
+    """The four keys, always present, in canonical form — what gets stored
+    and what the UI/agent reads back. Call after validate_inception."""
+    choices = choices or {}
+    return {
+        "exclude_always_on_rulebooks": sorted(set(choices.get("exclude_always_on_rulebooks") or [])),
+        "subscribe_rulebooks": sorted(set(choices.get("subscribe_rulebooks") or [])),
+        "design_system_id": choices.get("design_system_id"),
+        "seed_systems": bool(choices.get("seed_systems", False)),
+    }
+
+
+def is_decided(project) -> bool:
+    """A project is decided once its inception record exists (any via)."""
+    return bool(getattr(project, "inception", None))
+
+
+async def current_defaults(user_id: int, project_id: int) -> dict:
+    """What the project inherits if nobody decides — the ask's payload.
+
+    {always_on_rulebooks: [{id,title}], other_rulebooks: [{id,title}],
+     excluded_always_on: [...], subscribed_rulebooks: [...],
+     design_system_id, design_systems: [{id,title}], systems: <count>}.
+    Instance-agnostic: an install with no rulebooks / design systems shows
+    empty lists, and the ask says so rather than inventing a default.
+    """
+    from scribe.services import design_systems as design_systems_svc
+    from scribe.services import projects as projects_svc
+    from scribe.services import rulebooks as rulebooks_svc
+    from scribe.services import systems as systems_svc
+
+    project = await projects_svc.get_project(user_id, project_id)
+    if project is None:
+        raise ValueError(f"project {project_id} not found")
+    async with async_session() as session:
+        rows = (
+            await session.execute(
+                select(Rulebook.id, Rulebook.title, Rulebook.always_on)
+                .where(Rulebook.owner_user_id == user_id, Rulebook.deleted_at.is_(None))
+                .order_by(Rulebook.title)
+            )
+        ).all()
+    applicable = await rulebooks_svc.get_applicable_rules(project_id, user_id, limit=1)
+    designs = await design_systems_svc.list_design_systems(user_id)
+    systems = await systems_svc.list_systems(user_id, project_id, include_archived=True)
+    return {
+        "always_on_rulebooks": [{"id": i, "title": t} for i, t, on in rows if on],
+        "other_rulebooks": [{"id": i, "title": t} for i, t, on in rows if not on],
+        "excluded_always_on": applicable.get("excluded_always_on", []),
+        "subscribed_rulebooks": applicable.get("subscribed_rulebooks", []),
+        "design_system_id": project.design_system_id,
+        "design_systems": [{"id": d.id, "title": d.title} for d in designs],
+        "systems": len(systems),
+    }
+
+
+async def _check_targets(user_id: int, choices: dict) -> None:
+    """Every id a decision names must be the caller's (or readable) BEFORE any
+    effect lands — a decision applies whole or errors whole."""
+    from scribe.services import access
+
+    wanted = set(choices["exclude_always_on_rulebooks"]) | set(choices["subscribe_rulebooks"])
+    if wanted:
+        async with async_session() as session:
+            rows = (
+                await session.execute(
+                    select(Rulebook.id, Rulebook.always_on).where(
+                        Rulebook.id.in_(wanted),
+                        Rulebook.owner_user_id == user_id,
+                        Rulebook.deleted_at.is_(None),
+                    )
+                )
+            ).all()
+        found = {rid: on for rid, on in rows}
+        missing = sorted(wanted - set(found))
+        if missing:
+            raise ValueError(f"rulebook(s) {missing} not found (or not yours)")
+        not_always = sorted(r for r in choices["exclude_always_on_rulebooks"] if not found[r])
+        if not_always:
+            raise ValueError(
+                f"rulebook(s) {not_always} are not always-on — only always-on rulebooks "
+                "can be excluded; a subscribed rulebook is simply not subscribed"
+            )
+    ds = choices["design_system_id"]
+    if ds is not None and not await access.can_read_design_system(user_id, ds):
+        raise ValueError(f"design system {ds} not found (or not readable)")
+
+
+async def decide(
+    user_id: int,
+    project_id: int,
+    *,
+    choices: dict | None,
+    via: str,
+) -> dict:
+    """Record a project's inception decision and apply it (milestone 297).
+
+    Owner-only. Validates the choices (pure) and every target (owned /
+    readable) first; then, each idempotent: exclude the named always-on
+    rulebooks, subscribe the named rulebooks, point the project at the design
+    system (None = explicitly none), seed the standard Systems if asked and
+    the project has none; then write ``projects.inception`` LAST. Re-deciding
+    is additive for exclusions/subscriptions (nothing is silently dropped —
+    include/unsubscribe are explicit calls), replaces the design system, and
+    re-seeds nothing a project already has.
+
+    Returns {"inception": <record>, "effects": {excluded, subscribed,
+    design_system_id, systems_seeded}}.
+    """
+    from scribe.services import design_systems as design_systems_svc
+    from scribe.services import projects as projects_svc
+    from scribe.services import rulebooks as rulebooks_svc
+    from scribe.services import systems as systems_svc
+
+    if via not in INCEPTION_VIAS or via == "legacy":
+        raise ValueError("via must be 'mcp' or 'ui' ('legacy' is the migration's stamp)")
+    error = validate_inception(choices or {})
+    if error:
+        raise ValueError(error)
+    choices = normalize_choices(choices)
+    project = await projects_svc.get_project(user_id, project_id)   # owner-scoped
+    if project is None:
+        raise ValueError(f"project {project_id} not found (or not yours)")
+    await _check_targets(user_id, choices)
+
+    for rb in choices["exclude_always_on_rulebooks"]:
+        await rulebooks_svc.exclude_always_on_rulebook_for_project(project_id, rb, user_id)
+    for rb in choices["subscribe_rulebooks"]:
+        await rulebooks_svc.subscribe_project(project_id, rb, user_id)
+    if not await design_systems_svc.set_project_design_system(
+        user_id, project_id, choices["design_system_id"]
+    ):
+        raise ValueError("could not set the design system (no write on the project?)")
+    seeded = (
+        await systems_svc.seed_standard_systems(user_id, project_id)
+        if choices["seed_systems"] else []
+    )
+
+    record = {
+        "decided_at": datetime.now(timezone.utc).isoformat(),
+        "decided_by": user_id,
+        "via": via,
+        "choices": choices,
+    }
+    async with async_session() as session:
+        row = await session.get(Project, project_id)
+        row.inception = record
+        row.updated_at = datetime.now(timezone.utc)
+        await session.commit()
+    return {
+        "inception": record,
+        "effects": {
+            "excluded": choices["exclude_always_on_rulebooks"],
+            "subscribed": choices["subscribe_rulebooks"],
+            "design_system_id": choices["design_system_id"],
+            "systems_seeded": [sy.name for sy in seeded],
+        },
+    }
+
+
+async def inception_ask(user_id: int, project_id: int) -> dict:
+    """The enter_project ask for an undecided project (milestone 297) — the
+    sibling of the systems-bootstrap ask (#2683): the project's OWN current
+    defaults, what to ask the operator, and the exact call that answers it.
+    Fail-open: a hint must never break the call it rides on."""
+    try:
+        defaults = await current_defaults(user_id, project_id)
+    except Exception:
+        return {}
+    always = ", ".join(f"{r['title']} (#{r['id']})" for r in defaults["always_on_rulebooks"]) or "none"
+    others = ", ".join(f"{r['title']} (#{r['id']})" for r in defaults["other_rulebooks"]) or "none"
+    designs = ", ".join(f"{d['title']} (#{d['id']})" for d in defaults["design_systems"]) or "none"
+    return {
+        "defaults": defaults,
+        "ask": (
+            "This project has no inception decision: nobody has said what it "
+            f"inherits. Today, by default: always-on rulebooks binding it — {always}; "
+            f"rulebooks it could subscribe to — {others}; design system — "
+            f"{'#' + str(defaults['design_system_id']) if defaults['design_system_id'] else 'none'} "
+            f"(available: {designs}); Systems — {defaults['systems']}. Ask the operator, "
+            "once: which always-on rulebooks to EXCLUDE here (default: none), which "
+            "rulebooks to subscribe, which design system (or none), and whether to seed "
+            "the standard starter Systems — then record the answers. This ask repeats on "
+            "every enter_project until a decision is recorded."
+        ),
+        "call": (
+            f"decide_project_inception(project_id={project_id}, "
+            "exclude_always_on_rulebooks=[...], subscribe_rulebooks=[...], "
+            "design_system_id=<id | -1 for none>, seed_systems=<true|false>)"
+        ),
+    }
+

src/scribe/services/plugin_context.py

@@ -706,6 +706,7 @@ async def build_write_path_hint(
     exclude_sync_ids: list[int] | None = None,
     stamp_shapes: list[tuple[str, str]] | None = None,
     repo_key: str = "",
+    exclude_derive: list[str] | None = None,
 ) -> dict:
     """Prior-art hint for the plugin's PreToolUse hook on Write/Edit.
 
@@ -765,7 +766,7 @@ async def build_write_path_hint(
     """
     cfg = await get_writepath_config(user_id)
     empty = {"context": "", "note_ids": [], "sync_note_ids": [], "config": cfg,
-             "stamped": [], "divergence": []}
+             "stamped": [], "divergence": [], "derive": [], "derive_keys": []}
     path = (path or "").strip()
     if not cfg["enabled"] or not path:
         return empty
@@ -935,7 +936,20 @@ async def build_write_path_hint(
             )
         except Exception:
             logger.warning("write-time divergence check failed", exc_info=True)
-    if not synced and not menu and not stamped and not divergence:
+    # The in-band DERIVE check (#2900): the ledger's own knowledge of the
+    # names being written — a duplicate family with no canon, or a canon
+    # recorded elsewhere. This is the arm the by-name local grep could not
+    # be: it knows whether the other copies are canon or stray. Keyed per
+    # session (`exclude_derive`) so a family is named once, not per edit.
+    derive: list[dict] = []
+    if stamp_shapes and project_id:
+        try:
+            found = await shape_ledger_svc.write_time_derive(project_id, path, stamp_shapes)
+            skip = set(exclude_derive or [])
+            derive = [d for d in found if d.get("key") not in skip]
+        except Exception:
+            logger.warning("write-time derive check failed", exc_info=True)
+    if not synced and not menu and not stamped and not divergence and not derive:
         return empty
 
     owners = await owner_names_for({
@@ -1003,6 +1017,8 @@ async def build_write_path_hint(
         lines.append(_stamp_line(path, stamped))
     if divergence:
         lines.append(_divergence_line(path, divergence))
+    if derive:
+        lines.append(_derive_line(path, derive))
 
     # Split by arm, which is the whole reason this table exists. The place arm
     # carries no score and so has no home in retrieval_logs; before #2085 a
@@ -1027,9 +1043,40 @@ async def build_write_path_hint(
         "config": cfg,
         "stamped": stamped,
         "divergence": divergence,
+        "derive": derive,
+        "derive_keys": [d["key"] for d in derive],
     }
 
 
+def _derive_line(path: str, derive: list[dict]) -> str:
+    """The ledger's word on the names being written (#2900): a duplicate
+    family to derive, or a canon to reuse — said at the write."""
+    parts = []
+    for d in derive:
+        if d.get("canon"):
+            c = d["canon"]
+            parts.append(
+                f"`{c['label']}` is canon — snippet #{c['snippet_id']} at `{c['path']}`; "
+                "pull it and reuse, don't redefine"
+            )
+            continue
+        f = d["family"]
+        how = "identical body" if f.get("identical") else "same name defined"
+        files = ", ".join(f"`{x}`" for x in f.get("files") or [])
+        more = f.get("file_count", 0) - len(f.get("files") or [])
+        if more > 0:
+            files += f" +{more} more"
+        parts.append(
+            f"`{f['label']}` is a duplicate family with no canon — {how} in "
+            f"{f.get('file_count', 0)} other file(s): {files}; derive it now: "
+            "record the canon (create_snippet) and make the copies instances "
+            "(classify_shapes) — or, if these are convention not copies, "
+            "`classify_shapes(..., status=\"exempt\", reason_code=\"convention-plumbing\")` "
+            "dismisses the family — rather than adding another copy"
+        )
+    return f"> Shape ledger at `{path}`: " + "; ".join(parts) + "."
+
+
 def _divergence_line(path: str, divergence: list[dict]) -> str:
     """Button B where button A is canon — named at the write (#2793)."""
     parts = [
@@ -1097,7 +1144,14 @@ async def build_session_context(
     at _MAX_CHARS with an explicit truncation note so the hook can pass it
     through verbatim.
     """
-    rules = await rulebooks_svc.list_always_on_rules(user_id)
+    # Inside a project, the always-on set is the project's: an inception
+    # exclusion (milestone 297) takes a rulebook out of this block, and is
+    # named below so the departure is visible rather than silent.
+    rules = await rulebooks_svc.list_always_on_rules(user_id, project_id=project_id)
+    excluded = (
+        await rulebooks_svc.excluded_always_on_rulebooks(user_id, project_id)
+        if project_id else []
+    )
     topic_map = await _topic_titles({r.topic_id for r in rules if r.topic_id})
 
     lines: list[str] = [
@@ -1119,6 +1173,12 @@ async def build_session_context(
             heading = topic_map.get(r.topic_id, "ungrouped") if r.topic_id else "ungrouped"
             lines.append(f"### {heading}")
         lines.append(f"- [{r.id}] {r.title}")
+    if excluded:
+        names = ", ".join(f"{e['title']} (#{e['id']})" for e in excluded)
+        lines += [
+            "",
+            f"Excluded for this project by its inception decision (not binding here): {names}.",
+        ]
 
     project_dict: dict | None = None
     if project_id:

src/scribe/services/rulebooks.py

@@ -394,15 +394,57 @@ async def list_rules(
         return rulebook_rules + list(proj_result.scalars().all())
 
 
-async def list_always_on_rules(user_id: int, limit: int = 100) -> list[Rule]:
+def _excluded_rulebook_ids_q(project_id: int):
+    """Subquery: the always-on rulebooks this project opted out of at
+    inception (milestone 297) — used by every rule-resolution path so an
+    exclusion is total, not just cosmetic."""
+    from scribe.models.rulebook import project_rulebook_exclusions
+
+    return select(project_rulebook_exclusions.c.rulebook_id).where(
+        project_rulebook_exclusions.c.project_id == project_id
+    )
+
+
+async def excluded_always_on_rulebooks(user_id: int, project_id: int) -> list[dict]:
+    """[{id, title}] of the always-on rulebooks excluded for ``project_id``
+    (owner-scoped). Empty for an undecided or inherit-all project."""
+    from scribe.models.rulebook import project_rulebook_exclusions
+
+    if not project_id:
+        return []
+    async with async_session() as session:
+        rows = (
+            await session.execute(
+                select(Rulebook.id, Rulebook.title)
+                .join(project_rulebook_exclusions,
+                      project_rulebook_exclusions.c.rulebook_id == Rulebook.id)
+                .where(
+                    project_rulebook_exclusions.c.project_id == project_id,
+                    Rulebook.owner_user_id == user_id,
+                    Rulebook.deleted_at.is_(None),
+                )
+                .order_by(Rulebook.title)
+            )
+        ).all()
+    return [{"id": rid, "title": title} for rid, title in rows]
+
+
+async def list_always_on_rules(
+    user_id: int, limit: int = 100, project_id: int = 0,
+) -> list[Rule]:
     """Return all rules from rulebooks flagged always_on for the user.
 
     Called by the MCP tool of the same name at session start to load the
     standing rules that apply regardless of which project (if any) is in
     scope. Ordering matches list_rules so results are stable across calls.
+
+    ``project_id`` (milestone 297): inside a project that excluded specific
+    always-on rulebooks at inception, those rulebooks' rules are NOT
+    returned — the project decided not to inherit them. 0 = the user-wide
+    set, which is what a session sees before a project is in scope.
     """
     async with async_session() as session:
-        result = await session.execute(
+        q = (
             select(Rule)
             .join(RulebookTopic, Rule.topic_id == RulebookTopic.id)
             .join(Rulebook, RulebookTopic.rulebook_id == Rulebook.id)
@@ -413,10 +455,13 @@ async def list_always_on_rules(user_id: int, limit: int = 100) -> list[Rule]:
                 RulebookTopic.deleted_at.is_(None),
                 Rulebook.deleted_at.is_(None),
             )
-            .order_by(
+        )
+        if project_id:
+            q = q.where(Rulebook.id.notin_(_excluded_rulebook_ids_q(project_id)))
+        result = await session.execute(
+            q.order_by(
                 Rulebook.id, RulebookTopic.order_index, Rule.order_index, Rule.title,
-            )
+            ).limit(limit)
-            .limit(limit)
         )
         return list(result.scalars().all())
 
@@ -489,6 +534,7 @@ async def delete_rule(rule_id: int, user_id: int) -> None:
 # ── Subscriptions + get_applicable_rules ───────────────────────────────
 
 from sqlalchemy import insert, delete as sql_delete
+from sqlalchemy.exc import IntegrityError
 
 
 async def subscribe_project(
@@ -568,6 +614,51 @@ async def unsuppress_rule_for_project(
         await session.commit()
 
 
+async def exclude_always_on_rulebook_for_project(
+    project_id: int, rulebook_id: int, user_id: int,
+) -> None:
+    """Opt one project out of a whole ALWAYS-ON rulebook (milestone 297).
+    Owner-only on both sides; the rulebook must be always_on — a subscribed
+    rulebook is left by unsubscribing, not excluding. Idempotent."""
+    from scribe.models.rulebook import project_rulebook_exclusions
+
+    async with async_session() as session:
+        await _assert_project_owned(session, project_id, user_id)
+        await _assert_rulebook_owned(session, rulebook_id, user_id)
+        rb = await session.get(Rulebook, rulebook_id)
+        if rb is None or not rb.always_on:
+            raise ValueError(
+                f"rulebook {rulebook_id} is not always-on — it binds only by "
+                "subscription; unsubscribe_project_from_rulebook instead"
+            )
+        try:
+            await session.execute(
+                insert(project_rulebook_exclusions).values(
+                    project_id=project_id, rulebook_id=rulebook_id,
+                )
+            )
+            await session.commit()
+        except IntegrityError:
+            await session.rollback()  # already excluded — idempotent
+
+
+async def include_always_on_rulebook_for_project(
+    project_id: int, rulebook_id: int, user_id: int,
+) -> None:
+    """Undo exclude_always_on_rulebook_for_project. Idempotent."""
+    from scribe.models.rulebook import project_rulebook_exclusions
+
+    async with async_session() as session:
+        await _assert_project_owned(session, project_id, user_id)
+        await session.execute(
+            sql_delete(project_rulebook_exclusions).where(
+                project_rulebook_exclusions.c.project_id == project_id,
+                project_rulebook_exclusions.c.rulebook_id == rulebook_id,
+            )
+        )
+        await session.commit()
+
+
 async def suppress_topic_for_project(
     project_id: int, topic_id: int, user_id: int,
 ) -> None:
@@ -731,6 +822,9 @@ async def get_applicable_rules(
                 Rule.deleted_at.is_(None),
                 RulebookTopic.deleted_at.is_(None),
                 Rulebook.deleted_at.is_(None),
+                # An inception exclusion is total (milestone 297): a rulebook the
+                # project opted out of contributes nothing, subscribed or not.
+                Rulebook.id.notin_(_excluded_rulebook_ids_q(project_id)),
             )
             .order_by(
                 Rulebook.id, RulebookTopic.order_index, Rule.order_index, Rule.title,
@@ -778,6 +872,7 @@ async def get_applicable_rules(
         "suppressed_topics": suppressed_topics,
         "truncated": truncated,
         "subscribed_rulebooks": subscribed_rulebooks,
+        "excluded_always_on": await excluded_always_on_rulebooks(user_id, project_id),
     }
 
 
@@ -786,9 +881,12 @@ def rules_payload(applicable: dict) -> dict:
 
     Every surface that hands rules to an agent (enter_project, get_project,
     get_milestone, get_task for legacy plans, start_planning) carries the
-    same six keys under the same names — so a reader learns them once. One
+    same seven keys under the same names — so a reader learns them once. One
     place renames `rules` → `applicable_rules` and `truncated` →
     `applicable_rules_truncated`; the tools merge this into their payloads.
+    `excluded_always_on` (milestone 297) names the always-on rulebooks this
+    project decided NOT to inherit, so the departure is visible wherever the
+    rules are.
     """
     return {
         "applicable_rules": applicable["rules"],
@@ -797,4 +895,5 @@ def rules_payload(applicable: dict) -> dict:
         "project_rules": applicable.get("project_rules", []),
         "suppressed_rules": applicable.get("suppressed_rules", []),
         "suppressed_topics": applicable.get("suppressed_topics", []),
+        "excluded_always_on": applicable.get("excluded_always_on", []),
     }

src/scribe/services/shape_ledger.py

@@ -1225,7 +1225,6 @@ async def propose_for_repo(
                 select(CodeShape).where(
                     CodeShape.project_id == project_id,
                     CodeShape.repo_key == repo_key,
-                    CodeShape.status.in_(_MECHANICAL_TODO),
                     CodeShape.vanished_at.is_(None),
                 )
             )
@@ -1239,6 +1238,18 @@ async def propose_for_repo(
             examined_as = f"{body_sha}@{_PROPOSER_VERSION}"
             if row.proposed_at is not None and row.proposed_sha == examined_as:
                 continue
+            if row.status not in _MECHANICAL_TODO:
+                # A judged row gets no proposal — but its uses edges (#2870)
+                # are a fact about the body, judged or not: the consumer map
+                # of a canon must include the call sites someone already
+                # classified. Mark it examined so the scan runs once per body.
+                used = reference_canons(row.kind, row.path, row.symbol, body, canons)
+                if used:
+                    await record_uses(session, row, used, basis="reference",
+                                      evidence="proposer: body names the canon's symbol")
+                row.proposed_at = now
+                row.proposed_sha = examined_as
+                continue
             examined += 1
             group = row.proposal_group  # derive grouping is reassigned below
             hit = match_canon(
@@ -1393,6 +1404,34 @@ def proposal_summary(rows: Iterable[CodeShape], *, top: int = 8) -> dict:
     return {"proposed": proposed, "derive_groups": ranked[:top], "top_canon": top_canon}
 
 
+def derive_new_summary(
+    rows: Iterable[CodeShape], *, since: datetime | None, top: int = 3
+) -> dict:
+    """The arrival-moment drift signal (#2899): derive-grouped rows FIRST
+    SEEN after ``since`` — the previous refresh's stamp, the same one
+    flag_divergence uses. "Since the last refresh, N more copies joined a
+    duplicate family" is the sentence that makes the derive queue a thing
+    you notice on entering, not a thing an audit finds. ``since`` None (a
+    first seed) means nothing is new. Judged rows never count."""
+    if since is None:
+        return {"count": 0, "examples": []}
+    fresh = [
+        r for r in rows
+        if r.proposal_basis == "derive" and r.proposal_group
+        and r.status in _MECHANICAL_TODO and r.vanished_at is None
+        and r.created_at is not None and r.created_at > since
+    ]
+    fresh.sort(key=lambda r: r.created_at, reverse=True)
+    return {
+        "count": len(fresh),
+        "examples": [
+            {"label": ("." if r.kind == "css" else "") + r.symbol,
+             "path": r.path, "group": r.proposal_group}
+            for r in fresh[:top]
+        ],
+    }
+
+
 async def confirm_proposals(
     user_id: int,
     project_id: int,
@@ -1555,6 +1594,75 @@ async def write_time_divergence(
     return out
 
 
+# How many other files a family line names before "…" — enough to go look,
+# not a wall.
+_DERIVE_FILES_SHOWN = 4
+
+
+async def write_time_derive(
+    project_id: int, path: str, shapes: list[tuple[str, str]]
+) -> list[dict]:
+    """The in-band DERIVE check (#2900): for each (kind, name) the hook
+    named at ``path``, what the ledger already knows about that name
+    elsewhere in the project —
+
+      family  the name sits in a derive-first group (identical body in N
+              files, or the same name in ≥3): "this is a known duplicate
+              family with no canon — derive it now, don't add a copy";
+      canon   a `canonical` row of that name at another path: "this is
+              canon #N at <path> — reuse, don't redefine".
+
+    Only for shapes not yet judged at ``path`` (a judged shape is not
+    re-litigated at every edit), never for the canon's own file. Returns
+    [{symbol, kind, key, family?|canon?}] — `key` is the dedup token the
+    hook keeps per session (the group id, or canon:<snippet_id>)."""
+    wanted = {(k, _norm_symbol(n)): n for k, n in shapes if n}
+    if not wanted:
+        return []
+    async with async_session() as session:
+        rows = (
+            await session.execute(
+                select(CodeShape).where(
+                    CodeShape.project_id == project_id,
+                    CodeShape.vanished_at.is_(None),
+                    CodeShape.symbol.in_({norm for (_k, norm) in wanted}),
+                )
+            )
+        ).scalars().all()
+    out: list[dict] = []
+    for (kind, norm), name in wanted.items():
+        same = [r for r in rows if r.kind == kind and _norm_symbol(r.symbol) == norm]
+        here = next((r for r in same if r.path == path), None)
+        if here is not None and here.status not in _MECHANICAL_TODO:
+            continue  # judged here (or this IS the canon): nothing to say
+        others = [r for r in same if r.path != path]
+        label = ("." if kind == "css" else "") + name
+        canon = next((r for r in others if r.status == "canonical" and r.snippet_id), None)
+        if canon is not None:
+            out.append({"symbol": name, "kind": kind, "key": f"canon:{canon.snippet_id}",
+                        "canon": {"snippet_id": canon.snippet_id, "path": canon.path,
+                                  "label": label}})
+            continue
+        grouped = [r for r in others if r.proposal_group and r.status in _MECHANICAL_TODO]
+        if here is not None and here.proposal_group:
+            grouped = [r for r in grouped if r.proposal_group == here.proposal_group] or grouped
+        if not grouped:
+            continue
+        group = grouped[0].proposal_group
+        members = [r for r in grouped if r.proposal_group == group]
+        files = sorted({r.path for r in members})
+        out.append({
+            "symbol": name, "kind": kind, "key": group,
+            "family": {
+                "group": group, "label": label,
+                "identical": not group.startswith("name:"),
+                "files": files[:_DERIVE_FILES_SHOWN], "file_count": len(files),
+                "size": len(members) + (1 if here is not None else 0),
+            },
+        })
+    return out
+
+
 async def flag_divergence(project_id: int, *, since: datetime | None) -> int:
     """Flag shapes created after ``since`` (the previous refresh) that sit
     where a canon dominates and were not proposed as that canon. With no

src/scribe/services/systems.py

@@ -18,6 +18,41 @@ from scribe.services import access
 logger = logging.getLogger(__name__)
 
 
+# The standard cross-project vocabulary (#2798): names that mean the same
+# thing in every project, so a starter set reads the same everywhere. The
+# bootstrap ask (mcp/tools/systems) names them; the inception seed
+# (services/inception, milestone 297) mints them. Charters are deliberately
+# generic — a project refines them as its own records accrue.
+STANDARD_SYSTEMS: tuple[tuple[str, str], ...] = (
+    ("CI & Release", "How the project is verified and shipped: pipelines, runners, image/artifact builds, release tagging and rollback."),
+    ("Auth & Access", "Who may do what: identity, sessions/tokens, permissions and the scoping of every read and write to the right users."),
+    ("Data Model & Storage", "What is stored and how it is shaped: the schema, migrations, serialisation and the services that own a table's lifecycle."),
+    ("API Surface", "The doors into the capability: HTTP routes, tool/RPC surfaces, request parsing, error envelopes and their contracts."),
+    ("UI & Design", "What people see and touch: views, components, client state, and the design tokens/recipes they are built from."),
+    ("Import & Export", "Data crossing the boundary: backups, exports, imports, sync with other systems, file formats."),
+    ("Background Jobs", "Work that runs without a request: schedulers, queues, periodic ticks, retention and maintenance."),
+    ("Observability", "How the system reports on itself: logging, metrics, audit trails, health and diagnostics."),
+)
+
+
+async def seed_standard_systems(user_id: int, project_id: int) -> list[System]:
+    """Mint the standard starter set for a project that has NO Systems yet
+    (milestone 297). Idempotent: a project with any System — the vocabulary
+    already started, standard or not — gets nothing; the duplicate gate and
+    the project's own judgment take it from there. [] without write access."""
+    if await list_systems(user_id, project_id, include_archived=True):
+        return []
+    out: list[System] = []
+    for index, (name, charter) in enumerate(STANDARD_SYSTEMS):
+        system = await create_system(
+            user_id, project_id, name, description=charter, order_index=index,
+        )
+        if system is None:
+            break
+        out.append(system)
+    return out
+
+
 async def create_system(
     user_id: int,
     project_id: int,

tests/test_after_write_hook.py

@@ -0,0 +1,145 @@
+"""The PostToolUse after-write hook (#2901): code written through Bash — sed,
+heredocs, scripts — gets the same prior-art / ledger checks as a Write/Edit.
+
+Runs the real shell against a temp git repo and a throwaway HTTP sink, like
+the pre-write hook's end-to-end tests. Skips where the hook's tools are
+missing; asserts on content where they are present."""
+from __future__ import annotations
+
+import http.server
+import json
+import os
+import shutil
+import subprocess
+import threading
+import urllib.parse
+from pathlib import Path
+
+import pytest
+
+PLUGIN = Path(__file__).resolve().parents[1] / "plugin"
+HOOK = PLUGIN / "hooks" / "scribe_after_write.sh"
+
+
+def _env(tmp_path, url="http://127.0.0.1:9"):
+    for tool in ("git", "jq", "curl", "bash"):
+        if shutil.which(tool) is None:
+            pytest.skip(f"hook runtime tool {tool!r} not installed")
+    return {"PATH": os.environ["PATH"], "SCRIBE_URL": url, "SCRIBE_TOKEN": "t",
+            "TMPDIR": str(tmp_path), "HOME": str(tmp_path),
+            "GIT_AUTHOR_NAME": "t", "GIT_AUTHOR_EMAIL": "t@x", 
+            "GIT_COMMITTER_NAME": "t", "GIT_COMMITTER_EMAIL": "t@x"}
+
+
+def _repo(tmp_path, env):
+    repo = tmp_path / "repo"
+    repo.mkdir()
+    subprocess.run(["git", "init", "-q"], cwd=repo, check=True, env=env)
+    (repo / "b.py").write_text("def one():\n    return 1\n")
+    (repo / "c.py").write_text("def slug(t):\n    return t.lower()\n")
+    subprocess.run(["git", "add", "."], cwd=repo, check=True, env=env)
+    subprocess.run(["git", "commit", "-q", "-m", "base"], cwd=repo, check=True, env=env)
+    return repo
+
+
+def _run(repo, env, session="s-after-1", tool="Bash"):
+    out = subprocess.run(
+        ["bash", str(HOOK)],
+        input=json.dumps({"session_id": session, "cwd": str(repo), "tool_name": tool,
+                          "tool_input": {"command": "cat > x"}, "tool_response": {}}),
+        capture_output=True, text=True, env=env,
+    )
+    assert out.returncode == 0, out.stderr
+    return out.stdout
+
+
+class _Sink(http.server.BaseHTTPRequestHandler):
+    seen: list[dict] = []
+    reply = b'{"context":"> family named","note_ids":[],"sync_note_ids":[],"derive_keys":["dup:483a"]}'
+
+    def do_GET(self):
+        type(self).seen.append(urllib.parse.parse_qs(urllib.parse.urlparse(self.path).query))
+        self.send_response(200)
+        self.send_header("Content-Type", "application/json")
+        self.end_headers()
+        self.wfile.write(type(self).reply)
+
+    def log_message(self, *a):
+        pass
+
+
+@pytest.fixture
+def sink():
+    _Sink.seen = []
+    server = http.server.HTTPServer(("127.0.0.1", 0), _Sink)
+    threading.Thread(target=server.serve_forever, daemon=True).start()
+    try:
+        yield server
+    finally:
+        server.shutdown()
+
+
+def test_after_write_names_what_bash_just_wrote_then_stays_quiet_until_the_next_change(tmp_path, sink):
+    env = _env(tmp_path, url=f"http://127.0.0.1:{sink.server_port}")
+    repo = _repo(tmp_path, env)
+    # "A Bash call" wrote an untracked stylesheet and appended to a tracked file.
+    (repo / "a.css").write_text(".log-empty {\n  color: red;\n}\n")
+    (repo / "b.py").write_text("def one():\n    return 1\n\ndef slug(t):\n    return t\n")
+    out = _run(repo, env)
+    by_path = {q["path"][0]: q for q in _Sink.seen}
+    assert set(by_path) == {"a.css", "b.py"}           # repo-relative, like the pre hook
+    assert by_path["a.css"]["shapes"] == ["css:log-empty"]
+    assert by_path["b.py"]["shapes"] == ["sym:slug"]
+    # Added lines only for the tracked file — the existing def is not "just written".
+    assert "def slug" in by_path["b.py"]["code"][0] and "def one" not in by_path["b.py"]["code"][0]
+    ctx = json.loads(out)["hookSpecificOutput"]
+    assert ctx["hookEventName"] == "PostToolUse"
+    assert "> family named" in ctx["additionalContext"]
+    # The local by-name arm rides along: `slug` already lives in c.py.
+    assert "`slug` is already defined in 1 other file(s): c.py" in ctx["additionalContext"]
+    # Derive keys landed on the SHARED channel the pre-write hook reads.
+    state = tmp_path / "scribe-priorart" / "s-after-1.derive.ids"
+    assert "dup:483a" in state.read_text().split()
+
+    # Nothing changed → one git status, no request, no output.
+    _Sink.seen = []
+    assert _run(repo, env) == ""
+    assert _Sink.seen == []
+
+    # Another change → only that file, and the dedup channel goes back up.
+    (repo / "a.css").write_text(".log-empty {\n  color: red;\n}\n.other {\n  margin: 0;\n}\n")
+    _run(repo, env)
+    assert [q["path"][0] for q in _Sink.seen] == ["a.css"]
+    assert _Sink.seen[0]["exclude_derive"] == ["dup:483a"]
+    assert set(_Sink.seen[0]["shapes"][0].split(",")) == {"css:log-empty", "css:other"}
+
+
+def test_after_write_is_silent_where_it_has_nothing_to_say(tmp_path):
+    env = _env(tmp_path)
+    repo = _repo(tmp_path, env)
+    # Not a Bash call → nothing (hooks.json matches Bash, the script re-checks).
+    (repo / "a.css").write_text(".x {\n  color: red;\n}\n")
+    assert _run(repo, env, tool="Write") == ""
+    # Not a git repo → nothing.
+    loose = tmp_path / "loose"
+    loose.mkdir()
+    (loose / "a.css").write_text(".x {\n  color: red;\n}\n")
+    assert _run(loose, env, session="s-loose") == ""
+    # A change that defines nothing (prose, a call-site edit) → nothing, even
+    # with the server unreachable (port 9 refuses): no definitions, no arms.
+    (repo / "README.md").write_text("# notes\n")
+    (repo / "b.py").write_text("def one():\n    return one_more()\n")
+    assert _run(repo, env, session="s-quiet") == ""
+
+
+def test_after_write_local_arm_and_record_nudge_work_without_a_server(tmp_path):
+    """The local by-name arm needs no instance (#2280) and the record nudge
+    (#2664) fails open with it — a refused connection stands in for the
+    instance."""
+    env = _env(tmp_path)
+    repo = _repo(tmp_path, env)
+    (repo / "d.py").write_text("def slug(t):\n    return t.lower()\n")
+    out = _run(repo, env, session="s-local")
+    ctx = json.loads(out)["hookSpecificOutput"]["additionalContext"]
+    assert "`slug` is already defined in 1 other file(s): c.py" in ctx
+    assert "create_snippet" in ctx

tests/test_inception.py

@@ -0,0 +1,65 @@
+"""Project inception (milestone 297) — step 1: the record's shape.
+
+The WHY a project inherits what it does lives on projects.inception; the
+opt-out of an always-on rulebook is its own association table. Pure
+validation is pinned here; the effects are step 3's integration tests.
+"""
+from scribe.models import Base
+from scribe.models.project import Project
+from scribe.models.rulebook import project_rulebook_exclusions
+from scribe.services.inception import (
+    CHOICE_KEYS, INCEPTION_VIAS, is_decided, normalize_choices, validate_inception,
+)
+
+
+def test_project_carries_an_inception_record_and_to_dict_shows_it():
+    assert "inception" in Project.__table__.c
+    assert Project.__table__.c.inception.nullable   # NULL = undecided
+    p = Project(user_id=1, title="x", inception=None)
+    assert p.to_dict()["inception"] is None and not is_decided(p)
+    p.inception = {"via": "mcp", "decided_at": "2026-08-22T00:00:00+00:00", "decided_by": 1,
+                   "choices": normalize_choices({"seed_systems": True})}
+    assert is_decided(p) and p.to_dict()["inception"]["via"] == "mcp"
+    assert INCEPTION_VIAS == ("mcp", "ui", "legacy")
+
+
+def test_exclusions_table_is_the_suppressions_sibling():
+    t = Base.metadata.tables["project_rulebook_exclusions"]
+    assert project_rulebook_exclusions is t
+    assert {c.name for c in t.primary_key.columns} == {"project_id", "rulebook_id"}
+    fks = {fk.column.table.name: fk.ondelete for c in t.columns for fk in c.foreign_keys}
+    assert fks == {"projects": "CASCADE", "rulebooks": "CASCADE"}
+
+
+def test_validate_inception_pins_the_choice_vocabulary():
+    assert CHOICE_KEYS == ("exclude_always_on_rulebooks", "subscribe_rulebooks", "design_system_id", "seed_systems")
+    assert validate_inception({}) is None
+    assert validate_inception({"exclude_always_on_rulebooks": [1], "subscribe_rulebooks": [2],
+                               "design_system_id": 3, "seed_systems": True}) is None
+    assert validate_inception({"design_system_id": None}) is None
+    assert "must be an object" in validate_inception([])
+    assert "unknown inception choice" in validate_inception({"repo": "x"})
+    assert "list of rulebook ids" in validate_inception({"exclude_always_on_rulebooks": "1"})
+    assert "list of rulebook ids" in validate_inception({"subscribe_rulebooks": [0]})
+    assert "list of rulebook ids" in validate_inception({"subscribe_rulebooks": [True]})
+    assert "both excluded and subscribed" in validate_inception(
+        {"exclude_always_on_rulebooks": [1, 2], "subscribe_rulebooks": [2]})
+    assert "positive id or null" in validate_inception({"design_system_id": 0})
+    assert "positive id or null" in validate_inception({"design_system_id": True})
+    assert "true or false" in validate_inception({"seed_systems": "yes"})
+
+
+def test_normalize_choices_is_canonical_and_complete():
+    out = normalize_choices({"subscribe_rulebooks": [3, 1, 3], "exclude_always_on_rulebooks": [2]})
+    assert out == {"exclude_always_on_rulebooks": [2], "subscribe_rulebooks": [1, 3],
+                   "design_system_id": None, "seed_systems": False}
+    assert normalize_choices(None) == {"exclude_always_on_rulebooks": [], "subscribe_rulebooks": [],
+                                       "design_system_id": None, "seed_systems": False}
+
+
+def test_standard_systems_vocabulary_is_one_list_for_ask_and_seed():
+    from scribe.mcp.tools.systems import _STANDARD_SYSTEMS
+    from scribe.services.systems import STANDARD_SYSTEMS
+    assert _STANDARD_SYSTEMS == tuple(n for n, _ in STANDARD_SYSTEMS)
+    assert len(STANDARD_SYSTEMS) == 8 and all(charter for _, charter in STANDARD_SYSTEMS)
+

tests/test_inception_rules.py

@@ -0,0 +1,66 @@
+"""Milestone 297 step 2 — always-on exclusions reach every rule surface.
+
+The SQL is the integration lane's; here the contracts: rules_payload carries
+the seventh key, list_always_on_rules takes project_id, the session-start
+block names the excluded rulebooks, and the MCP tools mount.
+"""
+from unittest.mock import AsyncMock, patch
+
+import pytest
+
+from scribe.services.rulebooks import rules_payload
+
+
+def test_rules_payload_carries_excluded_always_on_as_the_seventh_key():
+    out = rules_payload({
+        "rules": [], "truncated": False, "subscribed_rulebooks": [],
+        "excluded_always_on": [{"id": 1, "title": "Family"}],
+    })
+    assert set(out) == {
+        "applicable_rules", "applicable_rules_truncated", "subscribed_rulebooks",
+        "project_rules", "suppressed_rules", "suppressed_topics", "excluded_always_on",
+    }
+    assert out["excluded_always_on"] == [{"id": 1, "title": "Family"}]
+    # An older applicable dict without the key still renders (empty list).
+    assert rules_payload({"rules": [], "truncated": False, "subscribed_rulebooks": []})["excluded_always_on"] == []
+
+
+def test_list_always_on_rules_service_and_tool_take_a_project_id():
+    import inspect
+
+    from scribe.mcp.tools import rulebooks as tools
+    from scribe.services import rulebooks as svc
+    assert "project_id" in inspect.signature(svc.list_always_on_rules).parameters
+    assert "project_id" in inspect.signature(tools.list_always_on_rules).parameters
+
+
+@pytest.mark.asyncio
+async def test_session_context_names_the_excluded_always_on_rulebooks():
+    from types import SimpleNamespace as NS
+
+    from scribe.services.plugin_context import build_session_context
+    rules = [NS(id=1, title="`dev` is home", topic_id=1, statement="x")]
+    project = NS(id=9, title="Widget", goal="", design_system_id=None)
+    with patch("scribe.services.plugin_context.rulebooks_svc.list_always_on_rules",
+               AsyncMock(return_value=rules)) as lao, \
+         patch("scribe.services.plugin_context.rulebooks_svc.excluded_always_on_rulebooks",
+               AsyncMock(return_value=[{"id": 5, "title": "Design standards"}])), \
+         patch("scribe.services.plugin_context._topic_titles", AsyncMock(return_value={1: "git"})), \
+         patch("scribe.services.plugin_context.projects_svc.get_project", AsyncMock(return_value=project)), \
+         patch("scribe.services.plugin_context.notes_svc.list_notes", AsyncMock(return_value=([], 0))), \
+         patch("scribe.services.plugin_context.rulebooks_svc.get_applicable_rules",
+               AsyncMock(return_value={"rules": [], "truncated": False, "subscribed_rulebooks": [],
+                                       "project_rules": [], "suppressed_rules": [],
+                                       "suppressed_topics": [], "excluded_always_on": []})):
+        out = await build_session_context(user_id=7, project_id=9)
+    # The always-on set was asked FOR THIS PROJECT, and the departure is named.
+    assert lao.await_args.kwargs.get("project_id") == 9
+    assert "Excluded for this project by its inception decision" in out["context"]
+    assert "Design standards (#5)" in out["context"]
+
+
+def test_exclusion_routes_are_registered():
+    from scribe.app import create_app
+    rules = {r.rule for r in create_app().url_map.iter_rules()}
+    assert "/api/projects/<int:project_id>/exclusions/rulebooks/<int:rulebook_id>" in rules
+

tests/test_integration_inception.py

@@ -0,0 +1,111 @@
+"""Real-Postgres integration tests for project inception (milestone 297).
+
+What mocks can't prove: a decision's effects land through the real services
+(exclusions filter the always-on set, subscriptions bind, the design system
+points, the standard Systems seed once), the record is written last, a bad
+target applies nothing.
+"""
+import pytest
+import pytest_asyncio
+
+from scribe.models import async_session
+from scribe.models.project import Project
+from scribe.models.rulebook import Rulebook
+from scribe.services import inception as inception_svc
+from scribe.services import rulebooks as rulebooks_svc
+from scribe.services import systems as systems_svc
+from tests.helpers import ensure_user
+
+pytestmark = [pytest.mark.integration, pytest.mark.usefixtures("_dispose_engine")]
+
+
+@pytest_asyncio.fixture
+async def seeded():
+    """Owner, a fresh project, one always-on rulebook (with a rule) and one
+    ordinary rulebook (with a rule)."""
+    async with async_session() as s:
+        owner = await ensure_user(s, "inception_owner")
+        project = Project(user_id=owner.id, title="Inception target")
+        s.add(project)
+        await s.flush()
+        ids = {"owner": owner.id, "pid": project.id}
+        await s.commit()
+    always = await rulebooks_svc.create_rulebook(ids["owner"], "Family standards")
+    other = await rulebooks_svc.create_rulebook(ids["owner"], "Optional practices")
+    async with async_session() as s:
+        rb = await s.get(Rulebook, always.id)
+        rb.always_on = True
+        await s.commit()
+    t1 = await rulebooks_svc.create_topic(always.id, ids["owner"], "git")
+    await rulebooks_svc.create_rule(t1.id, ids["owner"], "dev is home", "Work on dev.")
+    t2 = await rulebooks_svc.create_topic(other.id, ids["owner"], "docs")
+    await rulebooks_svc.create_rule(t2.id, ids["owner"], "Write the why", "Record reasons.")
+    ids.update({"always": always.id, "other": other.id})
+    return ids
+
+
+@pytest.mark.integration
+async def test_decide_applies_every_effect_and_records_last(seeded):
+    owner, pid = seeded["owner"], seeded["pid"]
+    # Undecided: the always-on rulebook binds, nothing subscribed, no Systems.
+    assert [r.title for r in await rulebooks_svc.list_always_on_rules(owner, project_id=pid)] == ["dev is home"]
+    defaults = await inception_svc.current_defaults(owner, pid)
+    assert [r["id"] for r in defaults["always_on_rulebooks"]] == [seeded["always"]]
+    assert [r["id"] for r in defaults["other_rulebooks"]] == [seeded["other"]]
+    assert defaults["systems"] == 0 and defaults["design_system_id"] is None
+
+    out = await inception_svc.decide(owner, pid, via="mcp", choices={
+        "exclude_always_on_rulebooks": [seeded["always"]],
+        "subscribe_rulebooks": [seeded["other"]],
+        "design_system_id": None,
+        "seed_systems": True,
+    })
+    assert out["effects"]["excluded"] == [seeded["always"]]
+    assert out["effects"]["subscribed"] == [seeded["other"]]
+    assert len(out["effects"]["systems_seeded"]) == len(systems_svc.STANDARD_SYSTEMS)
+
+    # The exclusion is total: the project's always-on set is empty, the
+    # departure is named, the subscription binds.
+    assert await rulebooks_svc.list_always_on_rules(owner, project_id=pid) == []
+    assert len(await rulebooks_svc.list_always_on_rules(owner)) == 1   # user-wide unchanged
+    applicable = await rulebooks_svc.get_applicable_rules(pid, owner)
+    assert [r["title"] for r in applicable["rules"]] == ["Write the why"]
+    assert [e["id"] for e in applicable["excluded_always_on"]] == [seeded["always"]]
+    assert [s["id"] for s in applicable["subscribed_rulebooks"]] == [seeded["other"]]
+    # The record, written last, says why.
+    async with async_session() as s:
+        project = await s.get(Project, pid)
+    assert inception_svc.is_decided(project)
+    assert project.inception["via"] == "mcp" and project.inception["decided_by"] == owner
+    assert project.inception["choices"]["exclude_always_on_rulebooks"] == [seeded["always"]]
+    # Re-deciding with seed again mints nothing twice; include reverses the exclusion.
+    again = await inception_svc.decide(owner, pid, via="ui", choices={"seed_systems": True})
+    assert again["effects"]["systems_seeded"] == []
+    assert len(await systems_svc.list_systems(owner, pid)) == len(systems_svc.STANDARD_SYSTEMS)
+    await rulebooks_svc.include_always_on_rulebook_for_project(pid, seeded["always"], owner)
+    assert [r.title for r in await rulebooks_svc.list_always_on_rules(owner, project_id=pid)] == ["dev is home"]
+
+
+@pytest.mark.integration
+async def test_a_bad_decision_applies_nothing(seeded):
+    owner, pid = seeded["owner"], seeded["pid"]
+    # Excluding a rulebook that is not always-on is refused BEFORE any effect.
+    with pytest.raises(ValueError, match="not always-on"):
+        await inception_svc.decide(owner, pid, via="mcp", choices={
+            "exclude_always_on_rulebooks": [seeded["other"]], "seed_systems": True,
+        })
+    assert await systems_svc.list_systems(owner, pid) == []
+    with pytest.raises(ValueError, match="not found"):
+        await inception_svc.decide(owner, pid, via="mcp", choices={"subscribe_rulebooks": [999999]})
+    with pytest.raises(ValueError, match="legacy"):
+        await inception_svc.decide(owner, pid, via="legacy", choices={})
+    async with async_session() as s:
+        project = await s.get(Project, pid)
+    assert not inception_svc.is_decided(project)
+    # An outsider cannot decide someone else's project.
+    async with async_session() as s:
+        other = await ensure_user(s, "inception_other")
+        other_id = other.id
+        await s.commit()
+    with pytest.raises(ValueError, match="not found"):
+        await inception_svc.decide(other_id, pid, via="mcp", choices={})

tests/test_integration_shape_classify.py

@@ -230,6 +230,19 @@ async def test_uses_edges_are_the_consumer_map(seeded):
     )
     assert out["classified"] == 1
     assert (await list_project_shapes(owner, pid, uses=hid))[1] == 2
+    # The proposer writes uses edges for JUDGED rows too: Config (exempt)
+    # names hash_token in its body → an edge, no proposal.
+    from scribe.services.shape_ledger import propose_for_repo
+    await classify_shapes(owner, pid, [
+        {"path": "src/app.py", "symbol": "Config", "status": "exempt", "reason": "settings"},
+    ])
+    defs = _defs(("src/app.py", "sym", "Config", "class Config:", "class Config:\n    token = hash_token(raw)\n"))
+    with _quiet_semantic():
+        await propose_for_repo(owner, pid, REPO, defs)
+    rows, total = await list_project_shapes(owner, pid, uses=hid)
+    assert total == 3 and {r.symbol for r in rows} >= {"Config"}
+    cfg = next(r for r in rows if r.symbol == "Config")
+    assert cfg.status == "exempt" and cfg.proposal is None
     with pytest.raises(ValueError):
         await classify_shapes(owner, pid, [
             {"path": "src/app.py", "symbol": "Config", "status": "exempt", "reason": "x", "uses": [999999]},
@@ -584,6 +597,82 @@ async def test_derive_groups_land_on_rows_and_in_the_summary(seeded):
     assert {r.symbol for r in rows} == {"slug"}                   # 2 files < the name floor
 
 
+@pytest.mark.integration
+async def test_write_time_derive_names_the_family_or_the_canon_for_a_name(seeded):
+    """#2900: against real rows — a name in a dup family → the family (other
+    files, count); a name whose canonical row lives elsewhere → that canon;
+    a judged row at the path, the canon's own file, or an unknown name →
+    silence."""
+    from scribe.services.shape_ledger import apply_derive_groups, write_time_derive
+
+    owner, pid, sid = seeded["owner"], seeded["pid"], seeded["snippet"]
+    defs = _defs(
+        ("v/A.vue", "css", "log-empty", ".log-empty {", ".log-empty { color: red }"),
+        ("v/B.vue", "css", "log-empty", ".log-empty {", ".log-empty { color: red }"),
+        ("v/C.vue", "css", "log-empty", ".log-empty {", ".log-empty { color: red }"),
+        ("src/factory.py", "sym", "factory", "def factory():", "def factory():\n    return 1"),
+    )
+    await sync_repo_shapes(pid, REPO, defs, seen_marker="m1")
+    await classify_shapes(owner, pid, [
+        {"path": "src/factory.py", "symbol": "factory", "status": "canonical", "snippet_id": sid},
+    ])
+    assert await apply_derive_groups(pid) >= 3
+
+    # A 4th copy about to be written → the family, naming the other files.
+    out = await write_time_derive(pid, "v/D.vue", [("css", "log-empty"), ("css", "unknown")])
+    assert len(out) == 1 and out[0]["symbol"] == "log-empty" and out[0]["kind"] == "css"
+    fam = out[0]["family"]
+    assert fam["identical"] is True and fam["label"] == ".log-empty"
+    assert fam["files"] == ["v/A.vue", "v/B.vue", "v/C.vue"] and fam["file_count"] == 3
+    assert out[0]["key"] == fam["group"] and fam["group"].startswith("dup:")
+    # Editing one existing member still names the OTHER members.
+    out = await write_time_derive(pid, "v/A.vue", [("css", "log-empty")])
+    assert out[0]["family"]["files"] == ["v/B.vue", "v/C.vue"] and out[0]["family"]["size"] == 3
+    # The canon's name elsewhere → the canon; in the canon's own file → silence.
+    out = await write_time_derive(pid, "src/other.py", [("sym", "factory")])
+    assert out == [{"symbol": "factory", "kind": "sym", "key": f"canon:{sid}",
+                    "canon": {"snippet_id": sid, "path": "src/factory.py", "label": "factory"}}]
+    assert await write_time_derive(pid, "src/factory.py", [("sym", "factory")]) == []
+    # A judged row at the path is not re-litigated.
+    await classify_shapes(owner, pid, [
+        {"path": "v/B.vue", "symbol": "log-empty", "status": "exempt", "reason": "print sheet"},
+    ])
+    assert await write_time_derive(pid, "v/B.vue", [("css", "log-empty")]) == []
+
+
+@pytest.mark.integration
+async def test_derive_new_names_the_copy_that_joined_a_family_since_the_stamp(seeded):
+    """#2899: the first sync seeds one `slug`; a later sync adds an identical
+    copy. Against the stamp between them, derive_new counts ONLY the
+    newcomer — the drift since the last refresh, not the whole family."""
+    from datetime import datetime, timezone
+
+    from scribe.services.shape_ledger import (
+        apply_derive_groups, derive_new_summary, live_rows,
+    )
+
+    owner, pid = seeded["owner"], seeded["pid"]
+    first = _defs(
+        ("a/one.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+    )
+    await sync_repo_shapes(pid, REPO, first, seen_marker="m1")
+    stamp = datetime.now(timezone.utc)
+    second = _defs(
+        ("a/one.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+        ("a/two.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+    )
+    await sync_repo_shapes(pid, REPO, second, seen_marker="m2")
+    assert await apply_derive_groups(pid) == 2
+
+    rows = await live_rows(pid)
+    out = derive_new_summary(rows, since=stamp)
+    assert out["count"] == 1
+    assert out["examples"][0]["path"] == "a/two.py"
+    assert out["examples"][0]["label"] == "slug"
+    assert out["examples"][0]["group"].startswith("dup:")
+    assert derive_new_summary(rows, since=None)["count"] == 0
+
+
 # --- #2793: the divergence readout against real rows -------------------------
 
 

tests/test_mcp_tool_projects.py

@@ -391,3 +391,81 @@ def test_enter_project_registered_in_register():
 
     register(mcp)
     assert "enter_project" in mcp.names
+
+
+# --- milestone 297: the inception doors ---------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_create_project_without_inception_args_stays_undecided():
+    p = fake_project(id=5, title="P", inception=None)
+    with patch("scribe.mcp.tools.projects.projects_svc.create_project", AsyncMock(return_value=p)), \
+         patch("scribe.mcp.tools.projects.inception_svc.decide", AsyncMock()) as decide:
+        out = await create_project(title="P")
+    decide.assert_not_awaited()
+    assert "inception_hint" in out and "inception_effects" not in out
+
+
+@pytest.mark.asyncio
+async def test_create_project_with_inception_args_decides_via_mcp():
+    p = fake_project(id=5, title="P", inception=None)
+    decided = {"inception": {"via": "mcp", "choices": {}}, "effects": {"systems_seeded": []}}
+    with patch("scribe.mcp.tools.projects.projects_svc.create_project", AsyncMock(return_value=p)), \
+         patch("scribe.mcp.tools.projects.inception_svc.decide", AsyncMock(return_value=decided)) as decide:
+        out = await create_project(title="P", exclude_always_on_rulebooks=[1], design_system_id=-1, seed_systems=True)
+    kw = decide.await_args.kwargs
+    assert decide.await_args.args[1] == 5 and kw["via"] == "mcp"
+    assert kw["choices"] == {"exclude_always_on_rulebooks": [1], "subscribe_rulebooks": [],
+                             "design_system_id": None, "seed_systems": True}
+    assert out["inception"]["via"] == "mcp" and "inception_effects" in out
+
+
+@pytest.mark.asyncio
+async def test_decide_project_inception_tool_records_an_inherit_all_decision_when_given_nothing():
+    from scribe.mcp.tools.projects import decide_project_inception
+    decided = {"inception": {"via": "mcp"}, "effects": {}}
+    with patch("scribe.mcp.tools.projects.inception_svc.decide", AsyncMock(return_value=decided)) as decide:
+        out = await decide_project_inception(project_id=5)
+    assert decide.await_args.kwargs["choices"] == {}
+    assert out["project_id"] == 5 and out["inception"]["via"] == "mcp"
+
+
+@pytest.mark.asyncio
+async def test_enter_project_carries_the_inception_ask_only_for_an_undecided_own_project():
+    applicable = {"rules": [], "project_rules": [], "truncated": False,
+                  "subscribed_rulebooks": [], "excluded_always_on": []}
+    ask = {"defaults": {}, "ask": "decide", "call": "decide_project_inception(...)"}
+
+    async def run(project):
+        with patch("scribe.mcp.tools.projects.projects_svc.get_project", AsyncMock(return_value=project)), \
+             patch("scribe.mcp.tools.projects.rulebooks_svc.get_applicable_rules", AsyncMock(return_value=applicable)), \
+             patch("scribe.mcp.tools.projects.milestones_svc.get_project_milestone_summary", AsyncMock(return_value=[])), \
+             patch("scribe.mcp.tools.projects.notes_svc.list_notes", AsyncMock(side_effect=[([], 0), ([], 0)])), \
+             patch("scribe.mcp.tools.projects.systems_svc.list_systems", AsyncMock(return_value=[])), \
+             patch("scribe.mcp.tools.projects.systems_tools.bootstrap_systems_ask", AsyncMock(return_value=None)), \
+             patch("scribe.mcp.tools.projects.inception_svc.inception_ask", AsyncMock(return_value=ask)) as asked:
+            return await enter_project(project_id=5), asked
+
+    # Own + undecided → the ask rides along.
+    out, asked = await run(fake_project(id=5, title="P", user_id=7, inception=None))
+    assert out["inception"] == ask and asked.await_count == 1
+    # Decided → absent, and the ask is not even built.
+    out, asked = await run(fake_project(id=5, title="P", user_id=7, inception={"via": "legacy"}))
+    assert "inception" not in out and asked.await_count == 0
+    # Someone else's (shared) project, undecided → not this caller's to decide.
+    out, asked = await run(fake_project(id=5, title="P", user_id=8, inception=None))
+    assert "inception" not in out and asked.await_count == 0
+
+
+def test_inception_routes_and_tool_are_registered():
+    from scribe.app import create_app
+    from scribe.mcp.server import build_mcp_server
+    rules = {r.rule for r in create_app().url_map.iter_rules()}
+    assert "/api/projects/<int:project_id>/inception" in rules
+    assert "/api/projects/<int:project_id>/inception/defaults" in rules
+    mcp = build_mcp_server()
+    assert mcp._tool_manager.get_tool("decide_project_inception") is not None
+    tool = mcp._tool_manager.get_tool("create_project")
+    for name in ("exclude_always_on_rulebooks", "subscribe_rulebooks", "design_system_id", "seed_systems"):
+        assert name in tool.parameters.get("properties", {}), name
+

tests/test_mcp_tool_rulebooks.py

@@ -169,12 +169,15 @@ def test_register_attaches_all_sixteen_tools():
     mcp = FakeMCP()
 
     register(mcp)
-    assert len(mcp.names) == 22
+    assert len(mcp.names) == 24   # +exclude/include_always_on_rulebook (milestone 297)
     # spot-check a few names
     assert "list_rulebooks" in mcp.names
     assert "create_rule" in mcp.names
     assert "subscribe_project_to_rulebook" in mcp.names
     assert "list_always_on_rules" in mcp.names
+    # milestone 297: a project's opt-out of a whole always-on rulebook
+    assert "exclude_always_on_rulebook" in mcp.names
+    assert "include_always_on_rulebook" in mcp.names
     assert "create_project_rule" in mcp.names
     assert "suppress_rule_for_project" in mcp.names
     assert "unsuppress_rule_for_project" in mcp.names

tests/test_pattern_coverage.py

@@ -276,6 +276,8 @@ async def test_coverage_measures_the_tree_exactly_and_caches(seeded):
     assert coverage["largest_gaps"] == [
         {"dir": "src", "unclassified": 2, "total": 3}
     ]
+    # #2899: a first computation has no previous stamp — nothing is "new".
+    assert coverage["derive_new"] == {"count": 0, "examples": []}
 
     # The walk fed the LEDGER (#2788): every extracted shape has a row, the
     # snippet reference locations are mechanically stamped canonical WITH
@@ -481,6 +483,13 @@ def test_extract_definitions_fingerprints_each_block():
     css = ".closed-msg {\n  text-align: center;\n  padding: 0.5rem 0;\n}\n.error-block {\n  text-align: center;\n  padding: 0.5rem 0;\n}\n.other {\n  text-align: left;\n}\n"
     d = {x.name: x for x in extract_definitions(css)}
     assert d["closed-msg"].body_sha == d["error-block"].body_sha != d["other"].body_sha
+    # One-line rules hash their own declarations — never the empty string
+    # (first deploy grouped 68 unrelated one-liners as one copy).
+    one = ".a { color: red; }\n\n.b { color: red; }\n\n.c { color: blue; }\n\n.d {\n  color: red;\n}\n"
+    e = {x.name: x for x in extract_definitions(one)}
+    import hashlib
+    assert e["a"].body_sha == e["b"].body_sha != e["c"].body_sha
+    assert e["a"].body_sha != hashlib.sha1(b"").hexdigest()[:16]
 
 
 def test_coverage_line_names_the_proposers_standing():
@@ -505,6 +514,41 @@ def test_coverage_line_names_the_proposers_standing():
     assert "top canon #2844 ×78" in line and "top copy closed-msg (identical body) ×3 files" in line
 
 
+def test_coverage_line_shows_standing_work_even_with_nothing_unclassified():
+    """#2899: since the scoped bucket a ledger can be fully accounted and
+    still carry derive groups / proposals / divergence — the line names
+    them as `standing:` instead of hiding them behind the todo count, and
+    names the drift since the previous refresh first-copy-first."""
+    from scribe.services.coverage import coverage_line
+
+    base = {
+        "total": 4693, "accounted": 4693, "unclassified": 0,
+        "counts": {"canonical": 37, "instance": 977, "variant": 73, "exempt": 1797, "scoped": 1809},
+        "computed_at": "2026-08-22T00:00:00+00:00", "largest_gaps": [],
+    }
+    quiet = coverage_line(base)
+    assert "unclassified" not in quiet and "standing" not in quiet
+    line = coverage_line({
+        **base,
+        "derive_groups": [{"group": "dup:abc", "label": "log-empty (identical body)", "files": 4}],
+        "derive_new": {"count": 2, "examples": [
+            {"label": ".error-msg", "path": "frontend/src/components/InceptionCard.vue", "group": "dup:9f0"},
+            {"label": ".error-msg", "path": "frontend/src/components/Other.vue", "group": "dup:9f0"},
+        ]},
+        "divergent": 1,
+    })
+    assert "; standing: 1 derive group, +2 new copies since last refresh: .error-msg in " \
+           "frontend/src/components/InceptionCard.vue, 1 DIVERGENT, top copy log-empty (identical body) ×4 files" in line
+    assert "unclassified" not in line
+    # One copy reads singular; with a todo the block keeps its old place.
+    one = coverage_line({**base, "derive_new": {"count": 1, "examples": []}})
+    assert one.endswith("; standing: +1 new copy since last refresh")
+    todo = coverage_line({**base, "unclassified": 3, "accounted": 4690, "proposed": 2,
+                          "derive_new": {"count": 1, "examples": [{"label": "x", "path": "a.py"}]},
+                          "largest_gaps": [{"dir": "src", "unclassified": 3, "total": 9}]})
+    assert "; 3 unclassified (2 proposed, +1 new copy since last refresh: x in a.py), largest: src" in todo
+
+
 def test_coverage_line_names_divergence_and_recheck():
     from scribe.services.coverage import coverage_line
 

tests/test_services_backup.py

@@ -18,7 +18,7 @@ def test_backup_version_is_v8():
     point of the test — a payload section added without moving the version
     produces backups that are structurally different and indistinguishable
     by inspection."""
-    assert backup.BACKUP_VERSION == 9
+    assert backup.BACKUP_VERSION == 10
 
 
 def test_not_included_lists_the_known_gaps():
@@ -116,7 +116,7 @@ async def test_export_full_backup_contains_every_declared_section():
                 "systems", "record_systems", "design_systems",
                 "design_tokens", "note_usage_events", "repo_bindings",
                 "note_supersessions", "code_shapes", "code_shape_events",
-                "code_shape_uses"):
+                "code_shape_uses", "rulebook_exclusions"):
         assert key in out, f"missing export section: {key}"
         assert out[key] == []
 

tests/test_services_plugin_context.py

@@ -4,6 +4,15 @@ import pytest
 from tests.helpers import fake_note
 
 
+@pytest.fixture(autouse=True)
+def _no_exclusions():
+    """build_session_context asks for the bound project's always-on
+    exclusions (milestone 297); these tests script the rules only."""
+    with patch("scribe.services.plugin_context.rulebooks_svc.excluded_always_on_rulebooks",
+               AsyncMock(return_value=[])):
+        yield
+
+
 pytestmark = pytest.mark.usefixtures("_no_supersession")
 
 

tests/test_services_rulebooks.py

@@ -8,6 +8,15 @@ import pytest
 from tests.helpers import fake_rule, fake_rulebook, fake_topic, make_mock_session
 
 
+@pytest.fixture(autouse=True)
+def _no_exclusions():
+    """get_applicable_rules asks for the project's always-on exclusions
+    (milestone 297) through its own session; these mocked-session tests
+    script the rule queries only, so the exclusions lookup is stubbed empty."""
+    with patch("scribe.services.rulebooks.excluded_always_on_rulebooks", AsyncMock(return_value=[])):
+        yield
+
+
 @pytest.mark.asyncio
 async def test_create_rulebook_stores_to_db():
     mock_session = make_mock_session()

tests/test_shape_ledger.py

@@ -317,6 +317,38 @@ def test_derive_groups_copy_before_name_with_floors():
     assert ("i.py", "sym", "one") not in g
 
 
+def test_derive_new_summary_counts_copies_first_seen_since_the_previous_refresh():
+    """#2899: the arrival-moment drift signal — derive-grouped rows created
+    after the previous refresh's stamp, newest first, judged rows and a
+    first seed (since=None) never count."""
+    from datetime import datetime, timedelta, timezone
+
+    from scribe.models.code_shape import CodeShape
+    from scribe.services.shape_ledger import derive_new_summary
+
+    t0 = datetime(2026, 8, 22, 12, 0, tzinfo=timezone.utc)
+
+    def row(path, symbol, at, kind="css", status="scoped", group="dup:abc", basis="derive"):
+        r = CodeShape(project_id=2, repo_key="r", path=path, symbol=symbol, kind=kind,
+                      status=status, proposal_basis=basis, proposal_group=group)
+        r.created_at = at
+        return r
+    rows = [
+        row("v/Old.vue", "error-msg", t0 - timedelta(days=3)),              # before the stamp
+        row("v/InceptionCard.vue", "error-msg", t0 + timedelta(hours=1)),   # new copy
+        row("v/Other.vue", "error-msg", t0 + timedelta(hours=2)),           # newer copy
+        row("v/J.vue", "error-msg", t0 + timedelta(hours=3), status="exempt"),   # judged: never
+        row("s/a.py", "load", t0 + timedelta(hours=1), kind="sym", group=None, basis=None),  # no family
+    ]
+    out = derive_new_summary(rows, since=t0)
+    assert out["count"] == 2
+    assert [e["path"] for e in out["examples"]] == ["v/Other.vue", "v/InceptionCard.vue"]
+    assert out["examples"][0] == {"label": ".error-msg", "path": "v/Other.vue", "group": "dup:abc"}
+    assert derive_new_summary(rows, since=None) == {"count": 0, "examples": []}
+    assert derive_new_summary(rows, since=t0, top=1)["examples"] == [
+        {"label": ".error-msg", "path": "v/Other.vue", "group": "dup:abc"}]
+
+
 def test_proposal_summary_ranks_body_identical_groups_first_and_sees_scoped_rows():
     """#2872: dup groups (the real copies) outrank name groups (usually
     convention), wider spread first; #2869: scoped rows are in the readout."""

tests/test_write_path_trigger.py

@@ -853,14 +853,18 @@ def test_hook_exits_silently_when_unconfigured():
 
 
 def test_hook_skips_prose_and_data_files():
-    """No round-trip for a markdown edit — the server would return nothing anyway."""
+    """No round-trip for a markdown edit — the server would return nothing
-    src = HOOK.read_text()
+    anyway. The list lives in the shared library (#2901) and the hook asks it."""
-    skip = re.search(r"case \"\$file_path\" in\n(.*?)esac", src, re.S)
+    lib = (PLUGIN / "hooks" / "scribe_defs.sh").read_text()
-    assert skip, "expected an extension skip list"
+    skip = re.search(r"scribe_skip_path\(\) \{\n  case \"\$1\" in\n(.*?)esac", lib, re.S)
+    assert skip, "expected an extension skip list in scribe_defs.sh"
     for ext in ("*.md", "*.json", "*.lock", "*.png"):
         assert ext in skip.group(1)
     # Config formats are deliberately NOT skipped — a workflow file is reusable.
     assert "*.yml" not in skip.group(1)
+    src = HOOK.read_text()
+    assert 'scribe_skip_path "$file_path" && exit 0' in src
+    assert '/scribe_defs.sh"' in src                   # sourced, not copied
 
 
 def test_plugin_version_bumped_with_the_hook():
@@ -1150,7 +1154,9 @@ def test_hook_names_the_shapes_being_written():
     that changes a body, not a signature — the definition enclosing the edit,
     found by walking the target file upward from the edited lines."""
     src = HOOK.read_text()
-    assert "scribe_defs()" in src                      # one extractor, two consumers
+    lib = (PLUGIN / "hooks" / "scribe_defs.sh").read_text()
+    assert "scribe_defs()" in lib                      # one extractor, shared (#2901)
+    assert "scribe_defs()" not in src                  # ...not a second copy here
     assert ".tool_input.old_string" in src             # the Edit's anchor
     assert "| tac | scribe_defs | head -1" in src      # nearest definition above
     # The ledger feed sends NAMES, never bodies, and stays on the one GET.
@@ -1243,6 +1249,116 @@ def test_hook_sends_the_enclosing_definition_for_a_body_edit(tmp_path):
     assert seen["shapes"] == ["sym:onTrash"]
 
 
+@pytest.mark.asyncio
+async def test_the_write_time_derive_check_names_a_family_or_a_canon_in_band():
+    """#2900: the ledger's own word on the names being written — a duplicate
+    family with no canon, or a canon recorded elsewhere — rendered at the
+    write even when nothing else does; keyed so the session's exclude
+    channel silences a family already named."""
+    from scribe.services import plugin_context as pc
+    found = [
+        {"symbol": "log-empty", "kind": "css", "key": "dup:483a",
+         "family": {"group": "dup:483a", "label": ".log-empty", "identical": True,
+                    "files": ["a/TaskLogSection.vue", "a/WorkspaceTaskPanel.vue"],
+                    "file_count": 5, "size": 6}},
+        {"symbol": "btn-primary", "kind": "css", "key": "canon:2855",
+         "canon": {"snippet_id": 2855, "path": "frontend/src/assets/components.css",
+                   "label": ".btn-primary"}},
+        {"symbol": "load", "kind": "sym", "key": "name:sym:load",
+         "family": {"group": "name:sym:load", "label": "load", "identical": False,
+                    "files": ["a/X.vue", "a/Y.vue", "a/Z.vue"], "file_count": 3, "size": 4}},
+    ]
+    check = AsyncMock(return_value=found)
+    patches = dict(
+        get_writepath_config=AsyncMock(return_value=_cfg()),
+        semantic_search_notes=AsyncMock(return_value=[]),
+        record_retrieval=MagicMock(), owner_names_for=AsyncMock(return_value={}),
+    )
+    with patch.multiple(pc, **patches), \
+         patch.object(pc.snippets_svc, "list_snippets", AsyncMock(return_value=([], 0))), \
+         patch.object(pc.shape_ledger_svc, "recent_pulls", AsyncMock(return_value={})), \
+         patch.object(pc.shape_ledger_svc, "write_time_divergence", AsyncMock(return_value=[])), \
+         patch.object(pc.shape_ledger_svc, "write_time_derive", check):
+        out = await pc.build_write_path_hint(
+            1, "frontend/src/components/New.vue", code=REAL_CODE, project_id=24,
+            stamp_shapes=[("css", "log-empty"), ("css", "btn-primary"), ("sym", "load")],
+            exclude_derive=["name:sym:load"],
+        )
+    check.assert_awaited_once_with(24, "frontend/src/components/New.vue",
+                                   [("css", "log-empty"), ("css", "btn-primary"), ("sym", "load")])
+    # The excluded family is gone; the other two render and are keyed.
+    assert [d["key"] for d in out["derive"]] == ["dup:483a", "canon:2855"]
+    assert out["derive_keys"] == ["dup:483a", "canon:2855"]
+    ctx = out["context"]
+    assert "Shape ledger at `frontend/src/components/New.vue`" in ctx
+    assert "`.log-empty` is a duplicate family with no canon — identical body in 5 other file(s): " \
+           "`a/TaskLogSection.vue`, `a/WorkspaceTaskPanel.vue` +3 more; derive it now" in ctx
+    assert "`.btn-primary` is canon — snippet #2855 at `frontend/src/assets/components.css`" in ctx
+    assert "convention-plumbing" in ctx
+    assert "`load`" not in ctx
+    # No project → no check; a failing check never sinks the hint.
+    check.reset_mock()
+    with patch.multiple(pc, **patches), \
+         patch.object(pc.snippets_svc, "list_snippets", AsyncMock(return_value=([], 0))), \
+         patch.object(pc.shape_ledger_svc, "recent_pulls", AsyncMock(return_value={})), \
+         patch.object(pc.shape_ledger_svc, "write_time_divergence", AsyncMock(return_value=[])), \
+         patch.object(pc.shape_ledger_svc, "write_time_derive", check):
+        out = await pc.build_write_path_hint(1, "x.py", code=REAL_CODE, stamp_shapes=[("sym", "f")])
+    check.assert_not_awaited()
+    assert out["derive"] == [] and out["derive_keys"] == []
+    boom = AsyncMock(side_effect=RuntimeError("ledger down"))
+    with patch.multiple(pc, **patches), \
+         patch.object(pc.snippets_svc, "list_snippets", AsyncMock(return_value=([], 0))), \
+         patch.object(pc.shape_ledger_svc, "recent_pulls", AsyncMock(return_value={})), \
+         patch.object(pc.shape_ledger_svc, "write_time_divergence", AsyncMock(return_value=[])), \
+         patch.object(pc.shape_ledger_svc, "write_time_derive", boom):
+        out = await pc.build_write_path_hint(1, "x.py", code=REAL_CODE, project_id=24,
+                                             stamp_shapes=[("sym", "f")])
+    assert out["context"] == "" and out["derive"] == []
+
+
+def test_the_hook_keeps_a_derive_channel_and_sends_it_back(tmp_path):
+    """#2900: derive keys the server returns land in the session's own
+    `.derive.ids` file and go back as `exclude_derive` on the next write —
+    a family is named once per session, not at every edit."""
+    import http.server
+    import threading
+    import urllib.parse
+
+    seen: list[dict] = []
+
+    class _Sink(http.server.BaseHTTPRequestHandler):
+        def do_GET(self):
+            seen.append(urllib.parse.parse_qs(urllib.parse.urlparse(self.path).query))
+            self.send_response(200)
+            self.send_header("Content-Type", "application/json")
+            self.end_headers()
+            self.wfile.write(b'{"context":"> family","note_ids":[],"sync_note_ids":[],'
+                             b'"derive_keys":["dup:483a","canon:2855"]}')
+
+        def log_message(self, *a):
+            pass
+
+    server = http.server.HTTPServer(("127.0.0.1", 0), _Sink)
+    threading.Thread(target=server.serve_forever, daemon=True).start()
+    try:
+        env = dict(_hook_runtime_env(), SCRIBE_URL=f"http://127.0.0.1:{server.server_port}",
+                   TMPDIR=str(tmp_path))
+        payload = {"session_id": "s-derive-1", "cwd": str(tmp_path), "tool_name": "Write",
+                   "tool_input": {"file_path": str(tmp_path / "a.css"),
+                                  "content": ".log-empty {\n  color: red;\n}\n"}}
+        for _ in range(2):
+            out = subprocess.run(["bash", str(HOOK)], input=json.dumps(payload),
+                                 capture_output=True, text=True, env=env)
+            assert out.returncode == 0, out.stderr
+    finally:
+        server.shutdown()
+    assert "exclude_derive" not in seen[0]
+    assert seen[1]["exclude_derive"] == ["dup:483a,canon:2855"]
+    state = tmp_path / "scribe-priorart" / "s-derive-1.derive.ids"
+    assert state.read_text().split() == ["dup:483a", "canon:2855", "dup:483a", "canon:2855"]
+
+
 @pytest.mark.asyncio
 async def test_the_write_time_divergence_check_is_named_in_band():
     """#2793: the hook named a shape at a path whose directory a canon