feat(family): platforms declared at inception and detected from bound repos (milestone 463 step 2, #4988)

A project's platforms decide which family ideas reach it. This step makes membership answerable from every door:

- services/platforms.py: the global catalog (writes are admin-only and duplicate-gated by slug); pure marker detection; and membership reads and writes. Detection only ADDS, and only where nobody has answered. It never overrides a declared or rejected row and never removes one.
- coverage: the archive scan now carries every path, and the refresh runs detection fail-open.
- inception: a platforms choice (slugs, or null for unanswered). The list is the whole answer: members left out of it become rejected.
- MCP: list_platforms and set_project_platforms; enter_project and get_project carry the project's platforms.
- REST: /api/platforms (admin writes) and /api/projects/<id>/platforms.
- UI: a platforms checklist on the inception card, a Family tab on ProjectView, and a Platforms admin tab in Settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/api/inception.ts

@@ -1,9 +1,14 @@
 /** Project inception (milestone 297): what a project was decided to inherit. */
 import { apiGet, apiPost } from "@/api/client";
+import type { ProjectPlatform } from "@/api/platforms";
 
 export interface InceptionChoices {
   design_system_id: number | null;
   seed_systems: boolean;
+  /** Platform slugs (milestone 463). null = not answered; a list is the
+   *  whole answer — members left out of it are recorded as "not this".
+   *  Absent on records decided before the question existed. */
+  platforms?: string[] | null;
 }
 
 export interface InceptionRecord {
@@ -17,16 +22,24 @@ export interface InceptionDefaults {
   design_system_id: number | null;
   design_systems: { id: number; title: string }[];
   systems: number;
+  platforms: { slug: string; name: string }[];
+  /** What detection (or an earlier answer) already says about the project. */
+  project_platforms: ProjectPlatform[];
 }
 
 export interface InceptionDecision {
   project_id: number;
   inception: InceptionRecord;
-  effects: { design_system_id: number | null; systems_seeded: string[] };
+  effects: {
+    design_system_id: number | null;
+    systems_seeded: string[];
+    /** The project's answers after the decision; null when left unstated. */
+    platforms: ProjectPlatform[] | null;
+  };
 }
 
 export const emptyChoices = (): InceptionChoices => ({
-  design_system_id: null, seed_systems: false,
+  design_system_id: null, seed_systems: false, platforms: null,
 });
 
 export const fetchInceptionDefaults = (projectId: number) =>

frontend/src/api/platforms.ts

@@ -0,0 +1,77 @@
+/**
+ * Platforms — what a project is built on or ships as (milestone 463).
+ *
+ * The catalog is GLOBAL, like the canonical areas, and admin-written. A
+ * project's answer per platform is `declared` (a person said so), `detected`
+ * (a marker file in a bound repo said so) or `rejected` (a person said no —
+ * kept, so the next refresh cannot detect it back). Only declared and
+ * detected make a project a member, and membership is what decides which
+ * family ideas reach it.
+ */
+import { apiGet, apiPatch, apiPost, apiPut } from "@/api/client";
+
+export interface Platform {
+  id: number;
+  name: string;
+  /** The match key, and the name every door takes (stable across restores). */
+  slug: string;
+  description: string | null;
+  /** Repo-relative globs. A bare name matches a basename anywhere; one with
+   *  a slash matches the whole path. Empty = declare-only. */
+  markers: string[];
+  order_index: number;
+  created_at: string | null;
+  updated_at: string | null;
+}
+
+export type PlatformState = "declared" | "detected" | "rejected";
+/** What a person may set. `null` withdraws the answer. */
+export type SettablePlatformState = "declared" | "rejected" | null;
+
+export interface ProjectPlatform {
+  id: number;
+  slug: string;
+  name: string;
+  state: PlatformState;
+}
+
+export const MEMBER_STATES: PlatformState[] = ["declared", "detected"];
+
+export async function listPlatforms(): Promise<Platform[]> {
+  const data = await apiGet<{ platforms: Platform[] }>("/api/platforms");
+  return data.platforms;
+}
+
+/** Admin only. A name that reduces to an existing slug answers 409. */
+export async function createPlatform(data: {
+  name: string;
+  description?: string;
+  markers?: string[];
+}): Promise<Platform> {
+  return apiPost("/api/platforms", data);
+}
+
+export async function updatePlatform(
+  id: number,
+  data: Partial<{ name: string; description: string; order_index: number; markers: string[] }>,
+): Promise<Platform> {
+  return apiPatch(`/api/platforms/${id}`, data);
+}
+
+export async function fetchProjectPlatforms(projectId: number): Promise<ProjectPlatform[]> {
+  const data = await apiGet<{ project_platforms: ProjectPlatform[] }>(
+    `/api/projects/${projectId}/platforms`,
+  );
+  return data.project_platforms;
+}
+
+/** Only the slugs named change; the update applies whole or not at all. */
+export async function setProjectPlatforms(
+  projectId: number,
+  platforms: Record<string, SettablePlatformState>,
+): Promise<ProjectPlatform[]> {
+  const data = await apiPut<{ project_platforms: ProjectPlatform[] }>(
+    `/api/projects/${projectId}/platforms`, { platforms },
+  );
+  return data.project_platforms;
+}

frontend/src/components/InceptionCard.vue

@@ -6,10 +6,16 @@
  * 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.
+ *
+ * Platforms (milestone 463) start UNANSWERED (null). Ticking any box makes
+ * the list the whole answer; in decide mode the boxes start from what
+ * detection already found, so recording confirms it.
  */
 import { computed, onMounted, ref, watch } from "vue";
 import { apiErrorMessage } from "@/api/client";
 import { fetchDesignSystems } from "@/api/designSystems";
+import { MEMBER_STATES } from "@/api/platforms";
+import { usePlatformsStore } from "@/stores/platforms";
 import {
   decideInception, emptyChoices, fetchInceptionDefaults,
   type InceptionChoices, type InceptionDecision, type InceptionDefaults,
@@ -29,6 +35,9 @@ const emit = defineEmits<{
 const local = ref<InceptionChoices>(props.choices ? { ...props.choices } : emptyChoices());
 const designSystems = ref<{ id: number; title: string }[]>([]);
 const systemsCount = ref(0);
+const platforms = ref<{ slug: string; name: string }[]>([]);
+const detected = ref<Set<string>>(new Set());
+const platformsStore = usePlatformsStore();
 const loading = ref(true);
 const saving = ref(false);
 const error = ref("");
@@ -46,11 +55,25 @@ async function load() {
       const d: InceptionDefaults = await fetchInceptionDefaults(props.projectId);
       designSystems.value = d.design_systems;
       systemsCount.value = d.systems;
+      platforms.value = d.platforms;
+      const members = d.project_platforms
+        .filter((p) => MEMBER_STATES.includes(p.state))
+        .map((p) => p.slug);
+      detected.value = new Set(
+        d.project_platforms.filter((p) => p.state === "detected").map((p) => p.slug),
+      );
       // Start from what stands today, so "record" without changes keeps it.
-      local.value = { design_system_id: d.design_system_id, seed_systems: false };
+      local.value = {
+        design_system_id: d.design_system_id,
+        seed_systems: false,
+        platforms: members.length ? members : null,
+      };
     } else {
-      const ds = await fetchDesignSystems();
+      const [ds, catalog] = await Promise.all([
+        fetchDesignSystems(), platformsStore.fetchCatalog(),
+      ]);
       designSystems.value = ds.design_systems.map((d) => ({ id: d.id, title: d.title }));
+      platforms.value = catalog.map((p) => ({ slug: p.slug, name: p.name }));
     }
   } catch (e: unknown) {
     error.value = apiErrorMessage(e, "Could not load what this project could inherit");
@@ -61,6 +84,22 @@ async function load() {
 
 const nothingToDecide = computed(() => !designSystems.value.length);
 
+function isChecked(slug: string): boolean {
+  return (local.value.platforms ?? []).includes(slug);
+}
+
+function togglePlatform(slug: string, on: boolean) {
+  const current = new Set(local.value.platforms ?? []);
+  if (on) current.add(slug);
+  else current.delete(slug);
+  local.value.platforms = [...current].sort();
+}
+
+/** Back to "not answered" — distinct from an empty list, which says "none". */
+function clearPlatforms() {
+  local.value.platforms = null;
+}
+
 async function record() {
   if (!props.projectId) return;
   saving.value = true;
@@ -105,6 +144,31 @@ onMounted(load);
           </span>
         </label>
       </div>
+      <div v-if="platforms.length" class="inception-group">
+        <h4>Platforms</h4>
+        <p class="inception-muted">
+          What it is built on or ships as. Ideas the family has proven for a
+          platform reach every project that is one.
+          <template v-if="local.platforms === null"> Not answered yet.</template>
+          <template v-else>
+            Anything left unticked is recorded as "not this project".
+            <button type="button" class="btn-ghost btn-sm" @click="clearPlatforms">Leave unanswered</button>
+          </template>
+        </p>
+        <div class="inception-platforms">
+          <label v-for="p in platforms" :key="p.slug" class="inception-choice">
+            <input
+              type="checkbox"
+              :checked="isChecked(p.slug)"
+              @change="togglePlatform(p.slug, ($event.target as HTMLInputElement).checked)"
+            />
+            <span>
+              {{ p.name }}
+              <em v-if="detected.has(p.slug)" class="inception-muted"> — detected</em>
+            </span>
+          </label>
+        </div>
+      </div>
       <p v-if="nothingToDecide" class="inception-muted">
         No design systems on this install yet — recording still settles the question.
       </p>
@@ -132,6 +196,11 @@ onMounted(load);
 .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-platforms {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(12rem, 1fr));
+  gap: 0 1rem;
+}
 .inception-select {
   padding: 0.45rem 0.7rem;
   border: 1px solid var(--fs-border-color);

frontend/src/components/ProjectFamilyTab.vue

@@ -0,0 +1,200 @@
+<script setup lang="ts">
+/**
+ * A project's place in the family (milestone 463): which platforms it is.
+ *
+ * Membership is what makes "does this family idea reach this project?" a
+ * lookup rather than a judgment — an idea is for some platforms, and it
+ * reaches every project that is one of them. So the answers here matter, and
+ * each kind of answer is shown as what it is:
+ *
+ * - Yes — a person said so.
+ * - Detected — a marker file in a bound repo said so. Detection only adds,
+ *   and only where nobody has answered; it never overrides a Yes or a No.
+ * - No — a person said this project is NOT that platform. Kept as a row, so
+ *   the next coverage refresh cannot detect it straight back.
+ * - No answer — detection may decide on the next refresh.
+ *
+ * Each change is saved as it is made: one platform, one request, applied
+ * whole or refused whole.
+ */
+import { computed, onMounted, ref, watch } from "vue";
+import { apiErrorMessage } from "@/api/client";
+import {
+  fetchProjectPlatforms, setProjectPlatforms,
+  type PlatformState, type ProjectPlatform, type SettablePlatformState,
+} from "@/api/platforms";
+import { usePlatformsStore } from "@/stores/platforms";
+
+const props = defineProps<{ projectId: number; canWrite: boolean }>();
+
+const platformsStore = usePlatformsStore();
+const answers = ref<ProjectPlatform[]>([]);
+const loading = ref(false);
+const failed = ref(false);
+const saving = ref<string | null>(null);
+const error = ref("");
+
+const LABELS: Record<PlatformState, string> = {
+  declared: "Yes",
+  detected: "Detected",
+  rejected: "No",
+};
+
+async function load() {
+  loading.value = true;
+  failed.value = false;
+  try {
+    const [, rows] = await Promise.all([
+      platformsStore.fetchCatalog(),
+      fetchProjectPlatforms(props.projectId),
+    ]);
+    answers.value = rows;
+  } catch {
+    // Said out loud: "couldn't load" must not read as "no platforms".
+    failed.value = true;
+  } finally {
+    loading.value = false;
+  }
+}
+
+const stateBySlug = computed(() => {
+  const out: Record<string, PlatformState> = {};
+  for (const a of answers.value) out[a.slug] = a.state;
+  return out;
+});
+
+const rows = computed(() =>
+  platformsStore.catalog.map((p) => ({
+    ...p,
+    state: stateBySlug.value[p.slug] ?? null,
+  })),
+);
+
+const memberCount = computed(
+  () => answers.value.filter((a) => a.state !== "rejected").length,
+);
+
+async function answer(slug: string, value: string) {
+  const state: SettablePlatformState = value === "" ? null : (value as SettablePlatformState);
+  saving.value = slug;
+  error.value = "";
+  try {
+    answers.value = await setProjectPlatforms(props.projectId, { [slug]: state });
+  } catch (e: unknown) {
+    error.value = apiErrorMessage(e, "Could not save that answer");
+  } finally {
+    saving.value = null;
+  }
+}
+
+onMounted(load);
+watch(() => props.projectId, load);
+</script>
+
+<template>
+  <div class="pft">
+    <header class="pft-head">
+      <h3 class="pft-title">Platforms</h3>
+      <p class="pft-muted">
+        What this project is built on or ships as. Ideas the family has proven
+        for a platform reach every project that is one, and each project
+        answers them — adopts, varies with a reason, or owes the work.
+      </p>
+    </header>
+
+    <p v-if="loading" class="pft-muted">Loading…</p>
+
+    <div v-else-if="failed" class="pft-note">
+      <strong>The platforms couldn't load.</strong>
+      <p>Nothing is known either way — this is a failure, not an empty answer.</p>
+      <button class="btn-secondary btn-sm" @click="load">Try again</button>
+    </div>
+
+    <p v-else-if="!rows.length" class="pft-muted">
+      This install has no platforms in its catalog yet. An administrator adds
+      them in Settings.
+    </p>
+
+    <template v-else>
+      <p class="pft-summary">
+        <template v-if="memberCount">
+          A member of {{ memberCount }} platform{{ memberCount === 1 ? "" : "s" }}.
+        </template>
+        <template v-else>
+          Not a member of any platform yet — bind a repo and refresh coverage
+          to detect them, or answer below.
+        </template>
+      </p>
+      <p v-if="error" class="error-msg">{{ error }}</p>
+      <ul class="pft-list">
+        <li v-for="p in rows" :key="p.id" class="pft-row">
+          <div class="pft-name">
+            <span>{{ p.name }}</span>
+            <span v-if="p.state" :class="['pft-tag', `pft-${p.state}`]">{{ LABELS[p.state] }}</span>
+            <span v-if="p.description" class="pft-desc">{{ p.description }}</span>
+          </div>
+          <select
+            v-if="canWrite"
+            class="pft-select"
+            :value="p.state === 'detected' ? 'detected' : (p.state ?? '')"
+            :disabled="saving === p.slug"
+            :aria-label="`Is this project ${p.name}?`"
+            @change="answer(p.slug, ($event.target as HTMLSelectElement).value)"
+          >
+            <option v-if="p.state === 'detected'" value="detected" disabled>Detected</option>
+            <option value="declared">Yes</option>
+            <option value="rejected">No</option>
+            <option value="">No answer</option>
+          </select>
+        </li>
+      </ul>
+    </template>
+  </div>
+</template>
+
+<style scoped>
+.pft { padding: 0.25rem 0; }
+.pft-head { margin-bottom: 1rem; }
+.pft-title { margin: 0 0 0.35rem; font-size: 1rem; }
+.pft-muted { color: var(--fs-text-tertiary); font-size: 0.875rem; margin: 0; }
+.pft-summary { color: var(--fs-text-secondary); font-size: 0.9rem; margin: 0 0 0.75rem; }
+.pft-note {
+  background: var(--fs-surface-raised);
+  border: 1px solid var(--fs-border-color);
+  border-radius: var(--fs-radius-md);
+  padding: 0.85rem 1rem;
+}
+.pft-note p { margin: 0.35rem 0 0.6rem; color: var(--fs-text-secondary); font-size: 0.875rem; }
+.pft-list { list-style: none; margin: 0; padding: 0; }
+.pft-row {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 1rem;
+  padding: 0.6rem 0;
+  border-bottom: 1px solid var(--fs-border-color);
+}
+.pft-name { display: flex; flex-wrap: wrap; align-items: baseline; gap: 0.25rem 0.5rem; min-width: 0; }
+.pft-desc { flex-basis: 100%; color: var(--fs-text-tertiary); font-size: 0.8rem; }
+.pft-tag {
+  font-size: 0.75rem;
+  padding: 0.05rem 0.45rem;
+  border-radius: var(--fs-radius-sm);
+  border: 1px solid var(--fs-border-color);
+  color: var(--fs-text-secondary);
+}
+.pft-declared { color: var(--fs-text-primary); }
+.pft-rejected { color: var(--fs-text-tertiary); text-decoration: line-through; }
+.pft-select {
+  padding: 0.35rem 0.6rem;
+  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: 0.85rem;
+  flex-shrink: 0;
+}
+@media (max-width: 640px) {
+  .pft-row { flex-direction: column; align-items: stretch; }
+}
+</style>

frontend/src/stores/platforms.ts

@@ -0,0 +1,48 @@
+import { ref } from "vue";
+import { defineStore } from "pinia";
+import * as api from "@/api/platforms";
+import type { Platform } from "@/api/platforms";
+
+/**
+ * The global platform catalog (milestone 463). Shared by every project, so
+ * it is fetched once per session — as the canonical-area catalog is.
+ */
+export const usePlatformsStore = defineStore("platforms", () => {
+  const catalog = ref<Platform[]>([]);
+  const loaded = ref(false);
+  const loading = ref(false);
+
+  async function fetchCatalog(force = false) {
+    if (loaded.value && !force) return catalog.value;
+    loading.value = true;
+    try {
+      catalog.value = await api.listPlatforms();
+      loaded.value = true;
+    } catch {
+      // The catalog is a vocabulary for a form; an empty one degrades the
+      // form rather than failing the screen it sits on.
+      catalog.value = [];
+    } finally {
+      loading.value = false;
+    }
+    return catalog.value;
+  }
+
+  async function createEntry(data: { name: string; description?: string; markers?: string[] }) {
+    const entry = await api.createPlatform(data);
+    catalog.value.push(entry);
+    return entry;
+  }
+
+  async function updateEntry(
+    id: number,
+    data: Partial<{ name: string; description: string; order_index: number; markers: string[] }>,
+  ) {
+    const entry = await api.updatePlatform(id, data);
+    const idx = catalog.value.findIndex((p) => p.id === id);
+    if (idx >= 0) catalog.value[idx] = entry;
+    return entry;
+  }
+
+  return { catalog, loaded, loading, fetchCatalog, createEntry, updateEntry };
+});

frontend/src/views/ProjectView.vue

@@ -12,6 +12,8 @@ import KindBadge from "@/components/KindBadge.vue";
 import ProjectStatusBadge from "@/components/ProjectStatusBadge.vue";
 import type { TaskKind } from "@/types/note";
 import ProjectDesignTab from "@/components/ProjectDesignTab.vue";
+import ProjectFamilyTab from "@/components/ProjectFamilyTab.vue";
+import { canWriteRecord } from "@/utils/permission";
 import ProjectRulesTab from "@/components/rules/ProjectRulesTab.vue";
 import SystemsSection from "@/components/SystemsSection.vue";
 import InceptionCard from "@/components/InceptionCard.vue";
@@ -125,7 +127,7 @@ async function confirmStartPlanning() {
 const saving = ref(false);
 const error = ref<string | null>(null);
 
-const activeTab = ref<"tasks" | "notes" | "systems" | "rules" | "design">("tasks");
+const activeTab = ref<"tasks" | "notes" | "systems" | "rules" | "design" | "family">("tasks");
 
 const tasks = ref<NoteItem[]>([]);
 const notes = ref<NoteItem[]>([]);
@@ -747,6 +749,10 @@ async function confirmDelete() {
         Inheritance decided {{ fmtDate(project.inception.decided_at) }} via {{ project.inception.via }}
         · 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>
+        <!-- What was said AT inception; the live answers are on the Family tab. -->
+        <template v-if="project.inception.choices.platforms?.length">
+          · platforms {{ project.inception.choices.platforms.join(", ") }}
+        </template>
       </p>
 
       <!-- Summary stat chips -->
@@ -945,6 +951,9 @@ async function confirmDelete() {
             <button :class="['tab-btn', { active: activeTab === 'design' }]" @click="activeTab = 'design'">
               Design
             </button>
+            <button :class="['tab-btn', { active: activeTab === 'family' }]" @click="activeTab = 'family'">
+              Family
+            </button>
           </div>
 
           <!-- Tasks tab — milestone-grouped kanban -->
@@ -1190,6 +1199,13 @@ async function confirmDelete() {
             :project-id="projectId"
             :design-system-id="project.design_system_id ?? null"
           />
+
+          <!-- Family tab (milestone 463): which platforms this project is. -->
+          <ProjectFamilyTab
+            v-if="activeTab === 'family'"
+            :project-id="projectId"
+            :can-write="canWriteRecord(project.permission)"
+          />
         </div>
       </div>
     </template>

frontend/src/views/SettingsView.vue

@@ -4,6 +4,7 @@ import { useSettingsStore } from "@/stores/settings";
 import { useAuthStore } from "@/stores/auth";
 import { useToastStore } from "@/stores/toast";
 import { useCanonicalSystemsStore } from "@/stores/canonicalSystems";
+import { usePlatformsStore } from "@/stores/platforms";
 import { apiGet, apiPost, apiPut, apiDelete, listGroups, createGroup, deleteGroup, listGroupMembers, addGroupMember, removeGroupMember, searchUsers, listApiKeys, createApiKey as apiCreateApiKey, revokeApiKey as apiRevokeApiKey, getProfile, updateProfile, type ApiKeyEntry, type GroupEntry, type GroupMember, type UserSearchResult, type UserProfile, apiErrorMessage } from "@/api/client";
 import type { User } from "@/types/auth";
 import PaginationBar from "@/components/PaginationBar.vue";
@@ -71,6 +72,75 @@ async function saveArea() {
     savingArea.value = false;
   }
 }
+// ── Platforms (milestone 463) ───────────────────────────────────────────
+// The global list of what a project can be built on or ship as. Same split
+// as the areas: admin-only to write, readable by everyone. Markers are the
+// repo-relative globs that let a coverage refresh DETECT a platform; they
+// are edited one per line, since a glob may itself contain a comma.
+const platformsStore = usePlatformsStore();
+const newPlatformName = ref("");
+const newPlatformDescription = ref("");
+const newPlatformMarkers = ref("");
+const creatingPlatform = ref(false);
+const editingPlatformId = ref<number | null>(null);
+const editPlatformName = ref("");
+const editPlatformDescription = ref("");
+const editPlatformMarkers = ref("");
+const savingPlatform = ref(false);
+
+function markerLines(text: string): string[] {
+  return text.split("\n").map((m) => m.trim()).filter(Boolean);
+}
+
+async function createPlatform() {
+  const name = newPlatformName.value.trim();
+  if (!name || creatingPlatform.value) return;
+  creatingPlatform.value = true;
+  try {
+    await platformsStore.createEntry({
+      name,
+      description: newPlatformDescription.value.trim() || undefined,
+      markers: markerLines(newPlatformMarkers.value),
+    });
+    newPlatformName.value = "";
+    newPlatformDescription.value = "";
+    newPlatformMarkers.value = "";
+    toastStore.show("Platform added");
+  } catch (e) {
+    // A 409 names the existing platform the new name reduces to.
+    toastStore.show(apiErrorMessage(e, "Failed to add platform"), "error");
+  } finally {
+    creatingPlatform.value = false;
+  }
+}
+
+function startEditPlatform(id: number, name: string, description: string | null, markers: string[]) {
+  editingPlatformId.value = id;
+  editPlatformName.value = name;
+  editPlatformDescription.value = description ?? "";
+  editPlatformMarkers.value = markers.join("\n");
+}
+
+async function savePlatform() {
+  const id = editingPlatformId.value;
+  const name = editPlatformName.value.trim();
+  if (id == null || !name || savingPlatform.value) return;
+  savingPlatform.value = true;
+  try {
+    await platformsStore.updateEntry(id, {
+      name,
+      description: editPlatformDescription.value.trim(),
+      markers: markerLines(editPlatformMarkers.value),
+    });
+    editingPlatformId.value = null;
+    toastStore.show("Platform updated");
+  } catch (e) {
+    toastStore.show(apiErrorMessage(e, "Failed to update platform"), "error");
+  } finally {
+    savingPlatform.value = false;
+  }
+}
+
 const userTimezone = ref("");
 const savingTimezone = ref(false);
 const timezoneSaved = ref(false);
@@ -479,7 +549,7 @@ async function copyCommit() {
 const restoreFileInput = ref<HTMLInputElement | null>(null);
 
 // Migrate stored "admin" → "config"; unknown tabs fall back to "general"
-const VALID_TABS = new Set(["general", "account", "profile", "notifications", "integrations", "data", "apikeys", "config", "users", "logs", "groups", "areas"]);
+const VALID_TABS = new Set(["general", "account", "profile", "notifications", "integrations", "data", "apikeys", "config", "users", "logs", "groups", "areas", "platforms"]);
 const _stored = localStorage.getItem("settings_tab") ?? "general";
 const activeTab = ref(VALID_TABS.has(_stored) ? (_stored === "admin" ? "config" : _stored) : "general");
 
@@ -489,6 +559,7 @@ function _loadTabContent(tab: string) {
     else if (tab === "logs") loadLogsPanel();
     else if (tab === "groups") loadGroupsPanel();
     else if (tab === "areas") canonStore.fetchCatalog(true);
+    else if (tab === "platforms") platformsStore.fetchCatalog(true);
     else if (tab === "config" && !versionInfo.value) loadVersionPanel();
   }
   if (tab === "apikeys") { fetchApiKeys(); }
@@ -1611,7 +1682,7 @@ async function deleteUser(userId: number) {
       <div v-if="authStore.isAdmin" class="sidebar-group">
         <div class="sidebar-group-label">Admin</div>
         <button
-          v-for="tab in ['config', 'areas', 'users', 'groups', 'logs']"
+          v-for="tab in ['config', 'areas', 'platforms', 'users', 'groups', 'logs']"
           :key="tab"
           :class="['sidebar-item', { active: activeTab === tab }]"
           @click="activeTab = tab"
@@ -3179,6 +3250,99 @@ async function deleteUser(userId: number) {
       </section>
     </div>
 
+    <!-- ── Platforms ── -->
+    <div v-if="authStore.isAdmin" v-show="activeTab === 'platforms'" class="settings-grid">
+      <section class="settings-section full-width">
+        <h2>Platforms</h2>
+        <p class="field-hint">
+          What a project can be built on or ship as. A project's platforms decide which family
+          ideas reach it. Markers are repo-relative file patterns, one per line: a bare name
+          (<code>go.mod</code>) matches that file anywhere in a bound repo, and a pattern with a
+          slash (<code>.github/workflows/*</code>) matches the whole path. A platform with no
+          markers is never detected — projects declare it themselves.
+        </p>
+
+        <ul class="area-admin-list">
+          <li v-for="entry in platformsStore.catalog" :key="entry.id" class="area-admin-row">
+            <template v-if="editingPlatformId === entry.id">
+              <form class="area-admin-form" @submit.prevent="savePlatform">
+                <input v-model="editPlatformName" class="fs-input" aria-label="Platform name" />
+                <textarea
+                  v-model="editPlatformDescription"
+                  class="fs-input"
+                  rows="2"
+                  aria-label="Platform description"
+                ></textarea>
+                <textarea
+                  v-model="editPlatformMarkers"
+                  class="fs-input area-admin-markers"
+                  rows="3"
+                  aria-label="Detection markers, one per line"
+                ></textarea>
+                <div class="area-admin-actions">
+                  <button type="submit" class="btn-primary btn-compact" :disabled="!editPlatformName.trim() || savingPlatform">
+                    {{ savingPlatform ? "Saving…" : "Save" }}
+                  </button>
+                  <button type="button" class="btn-ghost btn-compact" @click="editingPlatformId = null">Cancel</button>
+                </div>
+              </form>
+            </template>
+            <template v-else>
+              <div class="area-admin-body">
+                <div class="area-admin-name-row">
+                  <span class="area-admin-name">{{ entry.name }}</span>
+                  <code class="area-admin-slug" title="The match key, and the name tools and backups use.">{{ entry.slug }}</code>
+                </div>
+                <p v-if="entry.description" class="area-admin-desc">{{ entry.description }}</p>
+                <p class="area-admin-desc">
+                  <template v-if="entry.markers.length">
+                    Detected by
+                    <code v-for="m in entry.markers" :key="m" class="area-admin-slug">{{ m }}</code>
+                  </template>
+                  <template v-else>Declare-only — never detected.</template>
+                </p>
+              </div>
+              <button
+                class="btn-ghost btn-compact"
+                @click="startEditPlatform(entry.id, entry.name, entry.description, entry.markers)"
+              >Edit</button>
+            </template>
+          </li>
+        </ul>
+        <p v-if="!platformsStore.catalog.length && !platformsStore.loading" class="settings-empty">
+          No platforms yet.
+        </p>
+
+        <form class="area-admin-form area-admin-create" @submit.prevent="createPlatform">
+          <input
+            v-model="newPlatformName"
+            class="fs-input"
+            placeholder="New platform name (e.g. Flutter app)"
+            aria-label="New platform name"
+          />
+          <textarea
+            v-model="newPlatformDescription"
+            class="fs-input"
+            rows="2"
+            placeholder="What makes a project this platform? One sentence."
+            aria-label="New platform description"
+          ></textarea>
+          <textarea
+            v-model="newPlatformMarkers"
+            class="fs-input area-admin-markers"
+            rows="2"
+            placeholder="Markers, one per line (e.g. pubspec.yaml) — leave empty for declare-only"
+            aria-label="New platform markers, one per line"
+          ></textarea>
+          <div class="area-admin-actions">
+            <button type="submit" class="btn-primary btn-compact" :disabled="!newPlatformName.trim() || creatingPlatform">
+              {{ creatingPlatform ? "Adding…" : "Add platform" }}
+            </button>
+          </div>
+        </form>
+      </section>
+    </div>
+
     <div v-if="authStore.isAdmin" v-show="activeTab === 'users'" class="settings-grid">
 
       <section class="settings-section full-width">
@@ -4386,6 +4550,8 @@ async function deleteUser(userId: number) {
 .area-admin-form { display: flex; flex-direction: column; gap: 0.5rem; flex: 1; }
 .area-admin-create { margin-top: var(--fs-space-4); }
 .area-admin-actions { display: flex; gap: 0.4rem; }
+.area-admin-markers { font-family: var(--fs-font-mono); font-size: 0.82rem; }
+.area-admin-desc .area-admin-slug { margin-right: 0.25rem; }
 
 /* The retrieval tuning trail (#4102). Reads as a record, not a control panel:
    the operator is reviewing what was done, and the reason is the part worth