refactor: stabilize live chat sync materialization (#1132)

Canonicalize session message/part materialization across load, prefetch, reconnect, and recovery paths so OpenChamber restores session snapshots through one consistent merge flow.

Preserve live assistant streaming text when stale or delayed snapshots arrive, while still replacing optimistic user parts with confirmed server snapshots to avoid duplicated user messages.

Narrow recovery triggers to explicit incomplete snapshot signals instead of broad session-event fallbacks, reducing unnecessary session refetches during active streaming.

Keep turn windowing aligned with parented assistant replies and add regression coverage for materialization gaps, stale snapshot protection, optimistic user replacement, reconnect recovery, and turn grouping.

packages/ui/src/components/chat/lib/turns/windowTurns.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, test } from 'bun:test';
+import type { Message, Part } from '@opencode-ai/sdk/v2';
+import { buildTurnWindowModel, updateTurnWindowModelIncremental } from './windowTurns';
+import type { ChatMessageEntry } from './types';
+
+function message({ id, role, parentID }: { id: string; role: 'user' | 'assistant' | 'system'; parentID?: string }): ChatMessageEntry {
+    return {
+        info: {
+            id,
+            role,
+            ...(parentID ? { parentID } : {}),
+            time: { created: 1 },
+        } as Message,
+        parts: [] as Part[],
+    };
+}
+
+describe('windowTurns', () => {
+    test('does not map assistant messages without a parent to the current turn', () => {
+        const user = message({ id: 'u1', role: 'user' });
+        const assistant = message({ id: 'a1', role: 'assistant' });
+
+        const model = buildTurnWindowModel([user, assistant]);
+
+        expect(model.messageToTurnId.get('u1')).toBe('u1');
+        expect(model.messageToTurnId.has('a1')).toBe(false);
+    });
+
+    test('incremental update does not map assistant messages without a parent to the current turn', () => {
+        const user = message({ id: 'u1', role: 'user' });
+        const assistant = message({ id: 'a1', role: 'assistant' });
+        const base = buildTurnWindowModel([user]);
+
+        const next = updateTurnWindowModelIncremental(base, [user], [user, assistant]);
+
+        expect(next?.messageToTurnId.get('u1')).toBe('u1');
+        expect(next?.messageToTurnId.has('a1')).toBe(false);
+    });
+
+    test('maps assistant messages to their parent user turn', () => {
+        const user = message({ id: 'u1', role: 'user' });
+        const assistant = message({ id: 'a1', role: 'assistant', parentID: 'u1' });
+
+        const model = buildTurnWindowModel([user, assistant]);
+
+        expect(model.messageToTurnId.get('a1')).toBe('u1');
+    });
+});

packages/ui/src/components/chat/lib/turns/windowTurns.ts

@@ -119,9 +119,10 @@ export const updateTurnWindowModelIncremental = (
     }
 
     const parentId = resolveParentMessageId(nextMessage);
-    const targetTurnIndex = parentId
-        ? nextModel.turnIndexById.get(parentId)
-        : nextModel.turnIds.length - 1;
+    if (!parentId) {
+        return nextModel;
+    }
+    const targetTurnIndex = nextModel.turnIndexById.get(parentId);
     if (typeof targetTurnIndex !== 'number' || targetTurnIndex < 0) {
         return null;
     }
@@ -173,8 +174,13 @@ export const buildTurnWindowModel = (messages: ChatMessageEntry[]): TurnWindowMo
         }
 
         const parentId = resolveParentMessageId(message);
-        const parentTurnIndex = parentId ? userMessageToTurnIndex.get(parentId) : undefined;
-        const targetTurnIndex = typeof parentTurnIndex === 'number' ? parentTurnIndex : currentTurnIndex;
+        if (!parentId) {
+            return;
+        }
+        const targetTurnIndex = userMessageToTurnIndex.get(parentId);
+        if (typeof targetTurnIndex !== 'number') {
+            return;
+        }
         if (targetTurnIndex < 0) {
             return;
         }