feat(design): a project reports drift in its own recorded components

The check has taken a project id since it was written — check_snippets_against_
system(user_id, design_system_id, project_id=0), and the route has always read
?project_id=. Nothing on the frontend ever passed one and no project-side
surface existed, so the capability shipped and stayed unreachable.

A Design tab on the project, beside Systems and Rules, reporting three things
per snippet:

  no such token     var(--x) the system doesn't declare. Renders as NOTHING —
                    no error, no failing test, just an element quietly unstyled.
                    Leads for that reason.
  defines its own   a component minting a custom property instead of reaching
                    for the shared one. This is the DRY finding and the reason
                    the surface exists: the codebase re-solving a solved
                    problem, one component at a time, visible only when someone
                    changes the shared value and half the components don't move.
  write the token   a literal the sheet says to stop writing, paired with what
                    to write instead.

Three empty states, kept distinct, because collapsing them is how a check comes
to sit dead: no design system bound, no snippets recorded (nothing was
checked), and checked-and-clean. The last one says how many were checked.

Bound to the SAVED pointer rather than the sidebar picker's draft, so an
unsaved change can't make the tab report against a system the project isn't
using.

Scope is recorded code, per the operator: snippets are what Scribe holds, and a
repository's own sources are checked where they live, by that project's CI.

Step 3 of milestone #274.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaYUaouG9jjhATyuxCKrQs

frontend/src/api/designSystems.ts

@@ -200,6 +200,14 @@ export interface SnippetCheck {
   findings: SnippetFinding[];
 }
 
-/** Which recorded snippets disagree with this design system's sheet. */
-export const checkSnippets = (id: number) =>
-  apiGet<SnippetCheck>(`/api/design-systems/${id}/snippet-check`);
+/** Which recorded snippets disagree with this design system's sheet.
+ *
+ *  `projectId` narrows to the snippets one project owns — which is how a
+ *  project asks about its OWN code. Omit it to check every project, which is
+ *  the right default from the system's side: a component recorded elsewhere
+ *  still has to use the same tags. */
+export const checkSnippets = (id: number, projectId?: number) =>
+  apiGet<SnippetCheck>(
+    `/api/design-systems/${id}/snippet-check`
+    + (projectId ? `?project_id=${projectId}` : ""),
+  );

frontend/src/components/ProjectDesignTab.vue

@@ -0,0 +1,234 @@
+<script setup lang="ts">
+/**
+ * A project's own code, checked against the design system it is bound to (#2432).
+ *
+ * This is what the design surface is FOR: a project's recorded components
+ * measured against the sheet they are supposed to use. The check itself is not
+ * new — `check_snippets_against_system` has taken a project id since it was
+ * written, and the route has always read `?project_id=`. Nothing on this side
+ * ever passed one, so the capability shipped and stayed unreachable.
+ *
+ * The finding that matters most is the quiet one. `local_definitions` is a
+ * snippet minting its own custom property instead of reaching for the shared
+ * one — the codebase re-solving a solved problem, one component at a time.
+ * Nothing breaks, no test fails, and the duplication only becomes visible when
+ * someone changes the shared value and half the components don't move.
+ *
+ * SCOPE, and it is a limit rather than an omission: this reads RECORDED code —
+ * snippets — because that is the code Scribe holds. A repository's own sources
+ * are checked where they live, by that project's CI.
+ */
+import { onMounted, ref, watch } from "vue";
+
+import { checkSnippets, type SnippetCheck } from "@/api/designSystems";
+
+const props = defineProps<{ projectId: number; designSystemId: number | null }>();
+
+const check = ref<SnippetCheck | null>(null);
+const loading = ref(false);
+const failed = ref(false);
+
+async function run() {
+  check.value = null;
+  failed.value = false;
+  if (props.designSystemId === null) return;
+  loading.value = true;
+  try {
+    check.value = await checkSnippets(props.designSystemId, props.projectId);
+  } catch {
+    // Said out loud rather than rendered as an empty result. "Couldn't check"
+    // and "nothing to report" look identical if you let them, and that is how
+    // a check comes to sit dead without anyone noticing (#2419).
+    failed.value = true;
+  } finally {
+    loading.value = false;
+  }
+}
+
+onMounted(run);
+watch(() => [props.projectId, props.designSystemId], run);
+</script>
+
+<template>
+  <div class="pdt">
+    <div v-if="designSystemId === null" class="pdt-note">
+      <strong>No design system for this project.</strong>
+      <p>
+        Bind one in the sidebar and this tab reports where the project's recorded
+        components disagree with it — references to tokens the system doesn't
+        have, literals it says to stop writing, and properties a component mints
+        for itself instead of reusing.
+      </p>
+    </div>
+
+    <p v-else-if="loading" class="pdt-muted">Checking this project's snippets…</p>
+
+    <div v-else-if="failed" class="pdt-note">
+      <strong>The check couldn't run.</strong>
+      <p>Nothing was compared — this is a failure, not a clean result.</p>
+    </div>
+
+    <template v-else-if="check">
+      <p v-if="!check.checked" class="pdt-muted">
+        This project has no recorded snippets, so nothing was checked. Record the
+        components you reuse and they get measured against the sheet.
+      </p>
+
+      <p v-else-if="!check.findings.length" class="pdt-clean">
+        {{ check.checked }} snippet{{ check.checked === 1 ? "" : "s" }} checked —
+        every reference resolves, and none mints a property of its own.
+      </p>
+
+      <template v-else>
+        <p class="pdt-summary">
+          <strong>{{ check.findings.length }}</strong> of {{ check.checked }}
+          snippet{{ check.checked === 1 ? "" : "s" }} disagree with the sheet.
+        </p>
+
+        <ul class="pdt-list">
+          <li v-for="f in check.findings" :key="f.snippet_id" class="pdt-finding">
+            <router-link :to="`/snippets/${f.snippet_id}`" class="pdt-title">
+              {{ f.title || "Untitled snippet" }}
+            </router-link>
+
+            <!-- Renders as nothing at all: no error, no failing test, just an
+                 element that quietly isn't styled. Leads for that reason. -->
+            <div v-if="f.unknown.length" class="pdt-row">
+              <span class="pdt-tag unknown">no such token</span>
+              <span class="pdt-detail">
+                <code v-for="name in f.unknown" :key="name">{{ name }}</code>
+              </span>
+            </div>
+
+            <div v-if="f.local_definitions.length" class="pdt-row">
+              <span class="pdt-tag local">defines its own</span>
+              <span class="pdt-detail">
+                <code v-for="name in f.local_definitions" :key="name">{{ name }}</code>
+              </span>
+            </div>
+
+            <div v-if="f.superseded_literals.length" class="pdt-row">
+              <span class="pdt-tag superseded">write the token</span>
+              <span class="pdt-detail">
+                <span v-for="s in f.superseded_literals" :key="s.literal" class="pdt-swap">
+                  <code>{{ s.literal }}</code> → <code>{{ s.use_instead }}</code>
+                </span>
+              </span>
+            </div>
+          </li>
+        </ul>
+      </template>
+    </template>
+  </div>
+</template>
+
+<style scoped>
+.pdt {
+  padding: var(--fs-space-2) 0;
+}
+
+.pdt-note {
+  background: var(--color-surface);
+  border: 1px solid var(--color-border);
+  border-left: 3px solid var(--color-warning);
+  border-radius: var(--fs-radius-sm);
+  padding: var(--fs-space-3) var(--fs-space-4);
+}
+
+.pdt-note p {
+  margin: var(--fs-space-2) 0 0;
+  color: var(--color-text-secondary);
+  font-size: var(--fs-size-body-sm);
+  line-height: var(--fs-leading-body);
+  max-width: 70ch;
+}
+
+.pdt-muted,
+.pdt-clean,
+.pdt-summary {
+  color: var(--color-text-muted);
+  font-size: var(--fs-size-body-sm);
+  margin: 0 0 var(--fs-space-3);
+  max-width: 70ch;
+}
+
+.pdt-clean {
+  color: var(--color-status-done);
+}
+
+.pdt-summary {
+  color: var(--color-text-secondary);
+}
+
+.pdt-list {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  display: flex;
+  flex-direction: column;
+  gap: var(--fs-space-3);
+}
+
+.pdt-finding {
+  border: 1px solid var(--color-border);
+  border-radius: var(--fs-radius-md);
+  padding: var(--fs-space-3);
+  min-width: 0;
+}
+
+.pdt-title {
+  display: block;
+  font-weight: var(--fs-weight-medium);
+  color: var(--color-text);
+  text-decoration: none;
+  margin-bottom: var(--fs-space-2);
+}
+.pdt-title:hover { color: var(--color-primary-solid); }
+
+.pdt-row {
+  display: flex;
+  align-items: baseline;
+  gap: var(--fs-space-2);
+  flex-wrap: wrap;
+  padding: 0.15rem 0;
+  min-width: 0;
+}
+
+.pdt-tag {
+  font-size: var(--fs-size-tiny);
+  text-transform: uppercase;
+  letter-spacing: var(--fs-tracking-tiny);
+  padding: 0.1rem 0.45rem;
+  border-radius: var(--fs-radius-sm);
+  white-space: nowrap;
+  flex: none;
+}
+
+.pdt-tag.unknown {
+  background: var(--color-priority-high-bg);
+  color: var(--color-priority-high);
+}
+
+.pdt-tag.local {
+  background: var(--color-priority-medium-bg);
+  color: var(--color-priority-medium);
+}
+
+.pdt-tag.superseded {
+  background: var(--color-surface);
+  color: var(--color-text-muted);
+}
+
+.pdt-detail {
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--fs-space-2);
+  font-size: var(--fs-size-code);
+  color: var(--color-text-secondary);
+  min-width: 0;
+}
+
+.pdt-swap {
+  white-space: nowrap;
+}
+</style>

frontend/src/views/ProjectView.vue

@@ -7,6 +7,7 @@ import { useTasksStore } from "@/stores/tasks";
 import { relativeTime } from "@/composables/useRelativeTime";
 import { renderMarkdown } from "@/utils/markdown";
 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 {
@@ -108,7 +109,7 @@ async function confirmStartPlanning() {
 const saving = ref(false);
 const error = ref<string | null>(null);
 
-const activeTab = ref<"tasks" | "notes" | "systems" | "rules">("tasks");
+const activeTab = ref<"tasks" | "notes" | "systems" | "rules" | "design">("tasks");
 
 const tasks = ref<NoteItem[]>([]);
 const notes = ref<NoteItem[]>([]);
@@ -570,6 +571,9 @@ async function confirmDelete() {
             <button :class="['tab-btn', { active: activeTab === 'rules' }]" @click="activeTab = 'rules'">
               Rules
             </button>
+            <button :class="['tab-btn', { active: activeTab === 'design' }]" @click="activeTab = 'design'">
+              Design
+            </button>
           </div>
 
           <!-- Tasks tab — milestone-grouped kanban -->
@@ -784,6 +788,16 @@ async function confirmDelete() {
 
           <!-- Rules tab -->
           <ProjectRulesTab v-if="activeTab === 'rules'" :project-id="projectId" />
+
+          <!-- Design tab: this project's recorded components against its sheet.
+               Bound to the SAVED pointer rather than the picker's draft value,
+               so an unsaved change in the sidebar can't make the tab report on
+               a system this project isn't using. -->
+          <ProjectDesignTab
+            v-if="activeTab === 'design'"
+            :project-id="projectId"
+            :design-system-id="project.design_system_id ?? null"
+          />
         </div>
       </div>
     </template>