fix(chat): list quote-only user messages in the prompt navigator

Context parts are marked synthetic, so a message made only of quoted
fragments was skipped as an injected message and could not be navigated
to. Such turns now appear with the same caption the bubble shows.

packages/ui/src/lib/messages/contextParts.test.ts

@@ -6,6 +6,7 @@ import {
     contextPayloadFromDraft,
     createContextPart,
     formatContextText,
+    hasContextParts,
     readContextPart,
     type ContextPartPayload,
 } from './contextParts';
@@ -126,4 +127,11 @@ describe('round-trip through part metadata', () => {
             metadata: { [CONTEXT_METADATA_KEY]: { kind: 'github-issue', number: 0, title: 't', url: 'u' } },
         })).toBeNull();
     });
+
+    test('hasContextParts detects user-attached context in a message', () => {
+        const quote = asPart(contextPayloadFromDraft(draft({ source: 'chat-quote', fileLabel: 'msg_1' })));
+        expect(hasContextParts([quote])).toBe(true);
+        expect(hasContextParts([{ type: 'text' }])).toBe(false);
+        expect(hasContextParts([])).toBe(false);
+    });
 });

packages/ui/src/lib/messages/contextParts.ts

@@ -312,3 +312,8 @@ export function readContextPart(part: ContextCarrierPart): ContextPartPayload |
     const parsed = contextPayloadSchema.safeParse(part.metadata?.[CONTEXT_METADATA_KEY]);
     return parsed.success ? parsed.data : null;
 }
+
+/** Whether a message carries any user-attached context part. */
+export function hasContextParts(parts: ContextCarrierPart[]): boolean {
+    return parts.some((part) => readContextPart(part) !== null);
+}