4 files changed, 56 insertions, 0 deletions
diff --git a/src/adapters/idb/index.test.ts b/src/adapters/idb/index.test.ts
index 04e2177..aa56f15 100644
--- a/src/adapters/idb/index.test.ts
+++ b/src/adapters/idb/index.test.ts
@@ -128,3 +128,18 @@ describe("createIdbChunkStore", () => {
     expect(loaded2[0]?.chunk).toEqual(textChunk("b1"));
   });
 });
+
+it("persists epoch across adapter recreation and append, including empty histories", async () => {
+  const indexedDB = new IDBFactory();
+  const store = createIdbChunkStore({ indexedDB });
+  await store.append("c", [makeChunk(1, "legacy")]);
+  expect(await store.historyEpoch("c")).toBeUndefined();
+  await store.reset("c", 2);
+  const reopened = createIdbChunkStore({ indexedDB });
+  expect(await reopened.load("c")).toEqual([]);
+  expect(await reopened.historyEpoch("c")).toBe(2);
+  await reopened.append("c", [makeChunk(101, "new")]);
+  expect(await reopened.historyEpoch("c")).toBe(2);
+  await reopened.delete("c");
+  expect(await reopened.historyEpoch("c")).toBeUndefined();
+});
diff --git a/src/adapters/idb/index.ts b/src/adapters/idb/index.ts
index 3dffef9..8b1848a 100644
--- a/src/adapters/idb/index.ts
+++ b/src/adapters/idb/index.ts
@@ -20,6 +20,7 @@ interface ChunkRecord {
 interface MetaRecord {
   conversationId: string;
   lastAccess: number;
+  historyEpoch?: number;
 }
 
 export interface CreateIdbChunkStoreOptions {
@@ -92,6 +93,26 @@ export function createIdbChunkStore(opts?: CreateIdbChunkStoreOptions): Conversa
   }
 
   return {
+    async historyEpoch(conversationId) {
+      const db = await getDb();
+      const tx = db.transaction(META_STORE, "readonly");
+      const meta = await requestToPromise<MetaRecord | undefined>(
+        tx.objectStore(META_STORE).get(conversationId),
+      );
+      await txComplete(tx);
+      return meta?.historyEpoch;
+    },
+    async reset(conversationId, historyEpoch) {
+      const db = await getDb();
+      const tx = db.transaction([CHUNKS_STORE, META_STORE], "readwrite");
+      tx.objectStore(CHUNKS_STORE).delete(keyRangeFor(conversationId));
+      tx.objectStore(META_STORE).put({
+        conversationId,
+        historyEpoch,
+        lastAccess: Date.now(),
+      } satisfies MetaRecord);
+      await txComplete(tx);
+    },
     async load(conversationId: string): Promise<readonly StoredChunk[]> {
       const db = await getDb();
       const tx = db.transaction(CHUNKS_STORE, "readonly");
@@ -122,7 +143,9 @@ export function createIdbChunkStore(opts?: CreateIdbChunkStoreOptions): Conversa
         } satisfies ChunkRecord);
       }
 
+      const meta = await requestToPromise<MetaRecord | undefined>(metaStore.get(conversationId));
       metaStore.put({
+        ...meta,
         conversationId,
         lastAccess: Date.now(),
       } satisfies MetaRecord);
diff --git a/src/adapters/ws/logic.test.ts b/src/adapters/ws/logic.test.ts
index 2179ad0..4be2cd6 100644
--- a/src/adapters/ws/logic.test.ts
+++ b/src/adapters/ws/logic.test.ts
@@ -562,3 +562,18 @@ describe("parseServerMessage — subagent tab groups", () => {
     ).toBeNull();
   });
 });
+
+it("preserves a compaction epoch and rejects absent or invalid epochs", () => {
+  const msg = {
+    type: "conversation.compacted",
+    conversationId: "c",
+    newConversationId: "archive",
+    messagesSummarized: 2,
+    messagesKept: 1,
+    historyEpoch: 7,
+  };
+  expect(parseServerMessage(JSON.stringify(msg))).toEqual(msg);
+  for (const historyEpoch of [undefined, -1, 1.5, "7"]) {
+    expect(parseServerMessage(JSON.stringify({ ...msg, historyEpoch }))).toBeNull();
+  }
+});
diff --git a/src/adapters/ws/logic.ts b/src/adapters/ws/logic.ts
index cecc66c..858deaa 100644
--- a/src/adapters/ws/logic.ts
+++ b/src/adapters/ws/logic.ts
@@ -180,7 +180,10 @@ export function parseServerMessage(data: string): WsServerMessage | null {
       if (typeof parsed.newConversationId !== "string") return null;
       if (typeof parsed.messagesSummarized !== "number") return null;
       if (typeof parsed.messagesKept !== "number") return null;
+      if (!Number.isSafeInteger(parsed.historyEpoch) || (parsed.historyEpoch as number) < 0)
+        return null;
       const msg: ConversationCompactedMessage = {
+        historyEpoch: parsed.historyEpoch as number,
         type: "conversation.compacted",
         conversationId: parsed.conversationId,
         newConversationId: parsed.newConversationId,