fix(review-3.6): invalidate history caches by epoch and coalesce syncs

3 files changed, 68 insertions, 24 deletions

diff --git a/src/app/App.test.ts b/src/app/App.test.ts
index 26f5cdb..183b8b4 100644
--- a/src/app/App.test.ts
+++ b/src/app/App.test.ts
@@ -104,7 +104,9 @@ function fakeFetchImpl(): typeof fetch {
         { status: 200 },
       );
     }
-    return new Response(JSON.stringify({ chunks: [], latestSeq: 0 }), { status: 200 });
+    return new Response(JSON.stringify({ chunks: [], historyEpoch: 0, latestSeq: 0 }), {
+      status: 200,
+    });
   };
 }
 
@@ -564,7 +566,9 @@ describe("App component interaction tests", () => {
           status: 200,
         });
       }
-      return new Response(JSON.stringify({ chunks: [], latestSeq: 0 }), { status: 200 });
+      return new Response(JSON.stringify({ chunks: [], historyEpoch: 0, latestSeq: 0 }), {
+        status: 200,
+      });
     };
 
     const ws = fakeSocket();
diff --git a/src/app/store.svelte.ts b/src/app/store.svelte.ts
index c354e11..2eb13ef 100644
--- a/src/app/store.svelte.ts
+++ b/src/app/store.svelte.ts
@@ -704,7 +704,16 @@ function createHistorySync(httpBase: string, fetchImpl: typeof fetch): HistorySy
     if (!res.ok) {
       throw new Error(`History sync failed: ${res.status}`);
     }
-    return (await res.json()) as ConversationHistoryResponse;
+    const data = (await res.json()) as ConversationHistoryResponse;
+    if (
+      !data ||
+      !Array.isArray(data.chunks) ||
+      !Number.isSafeInteger(data.historyEpoch) ||
+      data.historyEpoch < 0
+    ) {
+      throw new Error("Invalid history response");
+    }
+    return data;
   };
 }
 
@@ -1483,6 +1492,13 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
       if (!res.ok) return;
       const data = (await res.json()) as ConversationListResponse;
 
+      if (!data || !Array.isArray(data.conversations)) {
+        reportError(
+          "Failed to load open conversations",
+          new Error("Invalid conversations response"),
+        );
+        return;
+      }
       // Update the status map from the authoritative backend list.
       const newStatuses = new Map<string, ConversationStatus>();
       for (const conv of data.conversations) {
@@ -1628,27 +1644,17 @@ export function createAppStore(opts?: CreateAppStoreOptions): AppStore {
       }
     },
     onConversationCompacted(msg: ConversationCompactedMessage): void {
-      // Compaction keeps the conversation ID — the old full history is forked
-      // to an archive (newConversationId). Just reload the same conversation's
-      // history (dispose stale store + cache + re-fetch).
       const cid = msg.conversationId;
-      const wasActive = tabsStore.activeConversationId === cid;
-      void cache.delete(cid);
-      if (!chatStores.has(cid) || !loadedConversationIds.delete(cid)) return;
-      const store = chatStores.get(cid);
-      if (store !== undefined) {
-        store.dispose();
-      }
-      const tab = tabsStore.tabs.find((t) => t.conversationId === cid);
-      const fresh = createChatFor(
-        cid,
-        tab?.model ?? activeModel,
-        tab?.workspaceId ?? activeWorkspaceId,
-      );
-      chatStores.set(cid, fresh);
-      ensureLoaded(cid);
-      if (wasActive) {
-        refreshActiveChat();
+      const store = chatStores.get(cid) ?? watchStores.get(cid);
+      if (store && loadedConversationIds.has(cid)) {
+        store.resync(msg.historyEpoch);
+      } else {
+        store?.invalidateHistory(msg.historyEpoch);
+        // Unseen conversations stay lazy. Invalidation is queued before their
+        // next load; epoch-guarded commits reject any older in-flight response.
+        void cache
+          .reset(cid, msg.historyEpoch)
+          .catch((err) => reportError("Failed to reset conversation cache", err));
       }
     },
     onReopen() {
diff --git a/src/app/store.test.ts b/src/app/store.test.ts
index f5d4723..f257f3a 100644
--- a/src/app/store.test.ts
+++ b/src/app/store.test.ts
@@ -195,7 +195,8 @@ function fakeFetchImpl(opts?: FakeFetchOptions): typeof fetch {
       }
       if (/^\/conversations\/[^/]+$/.test(pathname) && searchParams.has("sinceSeq")) {
         return Response.json(
-          history[url] ?? ({ chunks: [], latestSeq: 0 } satisfies ConversationHistoryResponse),
+          history[url] ??
+            ({ chunks: [], historyEpoch: 0, latestSeq: 0 } satisfies ConversationHistoryResponse),
         );
       }
     }
@@ -682,6 +683,7 @@ describe("createAppStore", () => {
         { seq: 1, role: "user", chunk: { type: "text", text: "hi" } },
         { seq: 2, role: "assistant", chunk: { type: "text", text: "hello!" } },
       ],
+      historyEpoch: 0,
       latestSeq: 2,
     };
     const base = fakeFetchImpl();
@@ -2743,6 +2745,7 @@ describe("conversation load-on-demand", () => {
             { seq: 1, role: "user", turnId: "t1", chunk: { type: "text", text: "hi" } },
             { seq: 2, role: "assistant", turnId: "t1", chunk: { type: "text", text: "hello" } },
           ],
+          historyEpoch: 0,
           latestSeq: 2,
         });
       }
@@ -2907,12 +2910,21 @@ describe("conversation load-on-demand", () => {
     const { store, requests } = await setup(ws);
     try {
       ws.resolveOpen();
+      ws.feedServerMessage({
+        type: "chat.delta",
+        event: { type: "turn-start", conversationId: "lazy-1", turnId: "old" },
+      });
+      ws.feedServerMessage({
+        type: "chat.delta",
+        event: { type: "text-delta", conversationId: "lazy-1", turnId: "old", delta: "stale" },
+      });
       for (const id of ["lazy-1", "unknown", "lazy-0"]) {
         ws.feedServerMessage({
           type: "conversation.compacted",
           conversationId: id,
           newConversationId: `${id}-archive`,
           messagesSummarized: 10,
+          historyEpoch: 0,
           messagesKept: 2,
         });
       }
@@ -2957,3 +2969,25 @@ describe("conversation load-on-demand", () => {
     }
   });
 });
+
+it.each([
+  null,
+  {},
+  { conversations: {} },
+])("reports malformed conversation lists: %j", async (body) => {
+  const ws = fakeSocket();
+  const base = fakeFetchImpl();
+  const store = createAppStore({
+    socketFactory: () => ws,
+    indexedDB: new IDBFactory(),
+    localStorage: createFakeStorage(),
+    fetchImpl: async (input, init) =>
+      String(input).includes("/conversations?status=") ? Response.json(body) : base(input, init),
+  });
+  try {
+    ws.resolveOpen();
+    await vi.waitFor(() => expect(store.fatalError).toContain("Invalid conversations response"));
+  } finally {
+    store.dispose();
+  }
+});