diff --git a/graph-ui/src/browser-ai/BrowserChatDock.test.tsx b/graph-ui/src/browser-ai/BrowserChatDock.test.tsx
index a91444d92..24852c865 100644
--- a/graph-ui/src/browser-ai/BrowserChatDock.test.tsx
+++ b/graph-ui/src/browser-ai/BrowserChatDock.test.tsx
@@ -1049,6 +1049,22 @@ describe('per-selection explanation cache', () => {
         await settleSelection(); expect(runtime.chat).toHaveBeenCalledOnce();
     });
 
+    it('explains again when a returning selection now carries other evidence, as after a re-index', async () => {
+        vi.useFakeTimers(); const { props, runtime } = fixture();
+        runtime.chat.mockResolvedValueOnce('Before the re-index.').mockResolvedValueOnce('Two layers.').mockResolvedValueOnce('After the re-index.');
+        await render({ ...props, proactive: true, proactiveSelection: jsonbAggEvidence() }); await click('Download & load');
+        await settleSelection(); expect(card()).toContain('Before the re-index.');
+        await render({ ...props, proactive: true, proactiveSelection: jsonbAggEvidence({ depth: 2 }) }); await settleSelection();
+        // The same selection, loading and then complete, after a re-index removed a caller.
+        await render({ ...props, proactive: true, proactiveSelection: jsonbAggEvidence({ state: 'loading-partial-preview' }) });
+        expect(card()).toContain('Before the re-index.');
+        await render({ ...props, proactive: true, proactiveSelection: jsonbAggEvidence({ edges: jsonbAggScope().edges.slice(2) }) });
+        expect(card()).not.toContain('Before the re-index.');
+        await settleSelection();
+        expect(runtime.chat).toHaveBeenCalledTimes(3);
+        expect(card()).toContain('After the re-index.');
+    });
+
     it('regenerates on request and keeps the cache bounded', async () => {
         vi.useFakeTimers(); const { props, runtime } = fixture();
         let calls = 0; runtime.chat.mockImplementation(async () => `Explanation number ${++calls}.`);
diff --git a/graph-ui/src/browser-ai/BrowserChatDock.tsx b/graph-ui/src/browser-ai/BrowserChatDock.tsx
index 50287daff..a94c7dc92 100644
--- a/graph-ui/src/browser-ai/BrowserChatDock.tsx
+++ b/graph-ui/src/browser-ai/BrowserChatDock.tsx
@@ -42,7 +42,7 @@ export interface BrowserChatDockProps {
 
 type Phase = 'off' | 'preparing' | 'ready' | 'counting' | 'generating' | 'removing';
 type ChatTurn = BrowserChatTurn & { evidence?: PreparedExplanationContext };
-type Explanation = { key: string; label: string; answer: string; status: string; error?: string; packet?: PreparedExplanationContext; citation?: ReturnType<typeof citedInterpretation>; mode?: 'interpretation'; shortened?: boolean };
+type Explanation = { key: string; label: string; answer: string; status: string; error?: string; packet?: PreparedExplanationContext; citation?: ReturnType<typeof citedInterpretation>; mode?: 'interpretation'; shortened?: boolean; evidence?: string };
 /** Finished explanations per selection, so returning to one does not run the model again. */
 const EXPLANATION_CACHE_SIZE = 32;
 const initialModel = BROWSER_MODELS.find(model => model.availability === 'available')!;
@@ -213,19 +213,25 @@ export default function BrowserChatDock({ proactiveSelection, selectionScope = "
         }
     }, [selected?.key, automatic, proactive]);
     useEffect(() => {
-        // Returning to an explained selection shows what was already written.
+        // Returning to an explained selection shows what was already written, unless its
+        // complete scope now carries other evidence, as after a re-index.
         const cached = selected && explanations.current.get(selected.key);
         if (!cached) return;
+        if (selected.evidence && cached.evidence !== selected.evidence) {
+            explanations.current.delete(selected.key); lastAttempt.current = undefined;
+            setExplanation(previous => previous?.key === selected.key ? undefined : previous);
+            return;
+        }
         lastAttempt.current = cached.key;
         setExplanation(previous => previous?.key === cached.key ? previous : cached);
-    }, [selected?.key]);
+    }, [selected?.key, selected?.evidence]);
     useEffect(() => {
         if (!historyReady || !proactive || !automatic || !selected || selected.waiting || phase !== 'ready' || manualRequest.current || pending.current
             || lastAttempt.current === selected.key || explanations.current.has(selected.key)) return;
         const snapshot = selected;
         const timer = setTimeout(() => { void explain(snapshot); }, EXPLANATION_DELAY_MS);
         return () => clearTimeout(timer);
-    }, [selected?.key, selected?.waiting, phase, automatic, proactive, retryExplanation, historyReady]);
+    }, [selected?.key, selected?.waiting, selected?.evidence, phase, automatic, proactive, retryExplanation, historyReady]);
     const remember = (entry: Explanation): void => {
         const cache = explanations.current;
         cache.delete(entry.key); cache.set(entry.key, entry);
@@ -269,7 +275,8 @@ export default function BrowserChatDock({ proactiveSelection, selectionScope = "
                 const result = parseExplanationResponse(answer, packet);
                 if (!followExplanation.current) setNewExplanation(true);
                 if (result.status === 'generated') {
-                    const complete: Explanation = { key: snapshot.key, label: snapshot.label, answer: result.markdown, status: 'complete', mode: 'interpretation', packet, citation: result.citation, ...shortened ? { shortened } : {} };
+                    const complete: Explanation = { key: snapshot.key, label: snapshot.label, answer: result.markdown, status: 'complete', mode: 'interpretation', packet, citation: result.citation,
+                        ...shortened ? { shortened } : {}, ...snapshot.evidence ? { evidence: snapshot.evidence } : {} };
                     remember(complete); setExplanation(complete);
                 } else setExplanation({ key: snapshot.key, label: snapshot.label, answer: '', status: 'error', packet, error: result.reason });
             }
diff --git a/graph-ui/src/browser-ai/proactive-selection.test.ts b/graph-ui/src/browser-ai/proactive-selection.test.ts
index 654b54b5d..0446a45b9 100644
--- a/graph-ui/src/browser-ai/proactive-selection.test.ts
+++ b/graph-ui/src/browser-ai/proactive-selection.test.ts
@@ -22,6 +22,15 @@ describe('selection identity for explanations', () => {
         expect(key('django-demo:galaxy', { id: 'o', label: 'OrderableAggMixin', text: JSON.stringify(other) })).not.toBe(base);
     });
 
+    it('fingerprints the evidence of a complete scope only, so a re-index can retire a cached explanation', () => {
+        const complete = explanationInput('p:galaxy', undefined, jsonbAggEvidence())!;
+        expect(complete.evidence).toBe(jsonbAggEvidence().id);
+        expect(explanationInput('p:galaxy', undefined, jsonbAggEvidence({ state: 'loading-partial-preview' }))?.evidence).toBeUndefined();
+        const reindexed = explanationInput('p:galaxy', undefined, jsonbAggEvidence({ edges: jsonbAggScope().edges.slice(2) }))!;
+        expect(reindexed.key).toBe(complete.key);
+        expect(reindexed.evidence).not.toBe(complete.evidence);
+    });
+
     it('marks incomplete Galaxy scopes as waiting and leaves other graph evidence unchanged', () => {
         expect(explanationInput('p:galaxy', undefined, jsonbAggEvidence())?.waiting).toBeUndefined();
         expect(explanationInput('p:galaxy', undefined, jsonbAggEvidence({ state: 'loading-partial-preview' }))?.waiting).toBe('loading');
diff --git a/graph-ui/src/browser-ai/proactive-selection.ts b/graph-ui/src/browser-ai/proactive-selection.ts
index 39fa82625..46733430b 100644
--- a/graph-ui/src/browser-ai/proactive-selection.ts
+++ b/graph-ui/src/browser-ai/proactive-selection.ts
@@ -11,6 +11,8 @@ export interface ExplanationInput {
     graph?: BrowserChatContext;
     /** A Galaxy scope that is not complete yet is shown, never explained. */
     waiting?: 'loading' | 'partial';
+    /** The complete scope's evidence: a cached explanation of other evidence (a re-index) is stale. */
+    evidence?: string;
 }
 
 /** Snapshot exact evidence; generated UI event IDs are not selection identity. */
@@ -26,7 +28,7 @@ export function explanationInput(scope: string, reader?: BrowserChatReaderContex
     if (galaxy) {
         // The selection and how its scope is drawn; counts and loading state change while it loads.
         const key = JSON.stringify([scope, 'galaxy', galaxy.identity, galaxy.direction, galaxy.edgeTypes, galaxy.depth]);
-        return { key, label: graph.label, graph: { ...graph }, ...galaxy.state === 'complete' ? {} : { waiting: galaxy.state } };
+        return { key, label: graph.label, graph: { ...graph }, ...galaxy.state === 'complete' ? { evidence: graph.id } : { waiting: galaxy.state } };
     }
     return { key: JSON.stringify([scope, graph.label, graph.text]), label: graph.label, graph: { ...graph } };
 }