fix(server): reverting a Claude thread to a subagent-only turn no longer breaks it

apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.test.ts

@@ -26,6 +26,7 @@ import {
   ChatAttachmentId,
   ChatFileAttachment,
   ChatImageAttachment,
+  CheckpointId,
   ClaudeSettings,
   EnvironmentId,
   MessageId,
@@ -3326,6 +3327,131 @@ describe("ClaudeAdapterV2 background wake turns", () => {
     ),
   );
 
+  const lastProviderTurn = (events: ReadonlyArray<ProviderAdapter.ProviderAdapterV2Event>) => {
+    const event = events.findLast((candidate) => candidate.type === "provider_turn.updated");
+    if (event?.type !== "provider_turn.updated") {
+      throw new Error("Expected a provider turn update.");
+    }
+    return event.providerTurn;
+  };
+  // Rollback closes the live query and waits for its message stream to end.
+  const makeRollbackHarness = makeWakeHarnessWithOptions({
+    close: (sdkMessages) => Queue.shutdown(sdkMessages),
+  });
+
+  it.effect(
+    "rolls back to the main-thread assistant message when a subagent frame comes last",
+    () =>
+      Effect.gen(function* () {
+        const harness = yield* makeRollbackHarness;
+        const now = yield* DateTime.now;
+        const mainUuid = "00000000-0000-4000-8000-000000000641";
+        yield* harness.runtime.startTurn(
+          makeClaudeTestTurnInput({
+            threadId: harness.threadId,
+            providerThread: harness.providerThread,
+            now,
+            attemptId: RunAttemptId.make("attempt-claude-cursor-main"),
+            text: "Continue.",
+            attachments: [],
+          }),
+        );
+        yield* Queue.offerAll(harness.sdkMessages, [
+          makeAssistantTextFrame({ uuid: mainUuid, text: "Delegating." }),
+          makeAssistantErrorFrame({
+            uuid: "00000000-0000-4000-8000-000000000642",
+            error: undefined,
+            parentToolUseId: "toolu_subagent",
+          }),
+          makeResultFrame({ uuid: "00000000-0000-4000-8000-000000000643", result: "Done." }),
+        ]);
+        yield* Queue.take(harness.terminalReceipts);
+
+        const providerTurn = lastProviderTurn(harness.events);
+        assert.equal(providerTurn.nativeTurnRef?.nativeId, mainUuid);
+        const rolledBack = yield* harness.runtime.rollbackThread({
+          providerThread: harness.providerThread,
+          target: {
+            type: "provider_turn",
+            checkpointId: CheckpointId.make("checkpoint-claude-cursor-main"),
+            appRunOrdinal: 1,
+            providerTurn,
+          },
+          providerThreadTurns: [
+            providerTurn,
+            {
+              ...providerTurn,
+              id: ProviderTurnId.make("provider-turn-claude-cursor-next"),
+              ordinal: 2,
+            },
+          ],
+        });
+        assert.equal(rolledBack.providerThread.nativeConversationHeadRef?.nativeId, mainUuid);
+      }).pipe(
+        Effect.provide(
+          Layer.mergeAll(IdAllocator.layer, McpProviderSessions.layer, NodeServices.layer),
+        ),
+      ),
+  );
+
+  it.effect("never records a subagent uuid for a turn with no main-thread assistant message", () =>
+    Effect.gen(function* () {
+      const harness = yield* makeRollbackHarness;
+      const now = yield* DateTime.now;
+      const subagentUuid = "00000000-0000-4000-8000-000000000644";
+      yield* harness.runtime.startTurn(
+        makeClaudeTestTurnInput({
+          threadId: harness.threadId,
+          providerThread: harness.providerThread,
+          now,
+          attemptId: RunAttemptId.make("attempt-claude-cursor-subagent-only"),
+          text: "Background task completed.",
+          attachments: [],
+        }),
+      );
+      yield* Queue.offerAll(harness.sdkMessages, [
+        makeAssistantErrorFrame({
+          uuid: subagentUuid,
+          error: undefined,
+          parentToolUseId: "toolu_subagent",
+        }),
+        makeResultFrame({ uuid: "00000000-0000-4000-8000-000000000645", result: "Done." }),
+      ]);
+      yield* Queue.take(harness.terminalReceipts);
+
+      const providerTurn = lastProviderTurn(harness.events);
+      assert.notEqual(providerTurn.nativeTurnRef?.nativeId, subagentUuid);
+      const rollbackTo = (providerThreadTurns: ReadonlyArray<typeof providerTurn>) =>
+        harness.runtime.rollbackThread({
+          providerThread: harness.providerThread,
+          target: {
+            type: "provider_turn",
+            checkpointId: CheckpointId.make("checkpoint-claude-cursor-subagent-only"),
+            appRunOrdinal: 1,
+            providerTurn,
+          },
+          providerThreadTurns,
+        });
+
+      const latest = yield* rollbackTo([providerTurn]);
+      assert.isNull(latest.providerThread.nativeConversationHeadRef);
+      const error = yield* rollbackTo([
+        providerTurn,
+        {
+          ...providerTurn,
+          id: ProviderTurnId.make("provider-turn-claude-cursor-next"),
+          ordinal: 2,
+        },
+      ]).pipe(Effect.flip);
+      assert.instanceOf(error, ProviderAdapter.ProviderAdapterRollbackThreadError);
+      assert.include(String(error.cause), "no SDK assistant message cursor");
+    }).pipe(
+      Effect.provide(
+        Layer.mergeAll(IdAllocator.layer, McpProviderSessions.layer, NodeServices.layer),
+      ),
+    ),
+  );
+
   it.effect.each([
     { recovered: false, expected: "Claude usage limit reached" },
     { recovered: true, expected: "Claude gave up after repeated API errors" },

apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts

@@ -6687,8 +6687,9 @@ export const makeClaudeAdapterV2 = Effect.fn("makeClaudeAdapterV2")(function* (
           }
 
           if (message.type === "assistant" && input.replayed !== true) {
-            context.nativeMessageCursor = message.uuid;
             if (message.parent_tool_use_id === null) {
+              // Subagent uuids exist only in the sidechain transcript, so resume and fork cannot target them.
+              context.nativeMessageCursor = message.uuid;
               context.latestAssistantRateLimited = message.error === "rate_limit";
               if (message.error === "authentication_failed") {
                 context.authenticationFailureMessage = claudeSignedOutMessage({