feat(ledger): divergence readout — button B where button A is canon, shape history, and judged-shape recheck (#2793, milestone 294 step 7)

Every judgment now goes through one helper that remembers the fingerprint
judged (classified_sha) and writes a code_shape_events row; the sync writes
vanished / reappeared / drifted events and flags recheck_at when a body
moves under an instance/variant. The refresh flags diverges_from on shapes
new since the previous computation that sit where one canon dominates the
judged siblings of their directory+kind and were not proposed as that canon
(a first seed flags nothing); the write-path hint asks the same question
in-band for the shapes the hook names. list_shapes(flag=divergence|recheck),
shape_history(project_id, path, symbol) (read-only), coverage line/payload/
card carry divergent + recheck. Backup v8 carries the history. Plugin 0.1.36.

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

frontend/src/views/ProjectView.vue

@@ -447,6 +447,17 @@ interface Coverage {
   // agent's confirm, and the biggest repeats-with-no-canon families.
   proposed?: number;
   derive_groups?: DeriveGroup[];
+  // The divergence readout (#2793): button B where button A is canon, and
+  // judged shapes whose bodies moved since they were judged.
+  divergent?: number;
+  divergence?: Divergence[];
+  recheck?: number;
+}
+interface Divergence {
+  path: string;
+  symbol: string;
+  kind: string;
+  canon_snippet_id: number;
 }
 
 const coverage = ref<Coverage | null>(null);
@@ -775,6 +786,28 @@ async function confirmDelete() {
               {{ g.label }} <span class="coverage-gap-count">×{{ g.size }}</span>
             </span>
           </div>
+          <div
+            v-if="coverage.divergent || coverage.recheck"
+            class="coverage-gaps"
+            title="Divergent: a new shape where one canon dominates its directory and that isn't proposed as that canon — button B where button A is canon. Recheck: a judged shape whose body changed since it was judged."
+          >
+            <span class="coverage-gaps-label">Divergence:</span>
+            <span
+              v-for="d in coverage.divergence || []"
+              :key="d.path + '::' + d.symbol"
+              class="coverage-gap-chip coverage-divergent"
+              :title="d.path + ' — canon here is snippet #' + d.canon_snippet_id"
+            >
+              {{ d.kind === 'css' ? '.' : '' }}{{ d.symbol }}
+              <span class="coverage-gap-count">→ #{{ d.canon_snippet_id }}</span>
+            </span>
+            <span v-if="(coverage.divergent || 0) > (coverage.divergence?.length || 0)" class="coverage-gap-chip">
+              +{{ (coverage.divergent || 0) - (coverage.divergence?.length || 0) }} more
+            </span>
+            <span v-if="coverage.recheck" class="coverage-gap-chip">
+              {{ coverage.recheck }} to recheck
+            </span>
+          </div>
         </template>
         <p v-else class="coverage-empty">
           Not measured yet — Refresh reads the bound repo's definitions into
@@ -1329,6 +1362,7 @@ async function confirmDelete() {
   font-size: 0.74rem;
 }
 .coverage-gap-count { opacity: 0.65; }
+.coverage-divergent { border-color: var(--fs-warning); }
 .coverage-empty {
   margin: 0;
   font-size: 0.8rem;