From f9e6d1290d56f5ae63f63cca4fdd231090d79a39 Mon Sep 17 00:00:00 2001
From: Julius Marminge <julius0216@outlook.com>
Date: Thu, 26 Feb 2026 21:13:00 -0800
Subject: [PATCH] Handle session restart failures without dropping active
 thread session

- Reorder restart flow to bind the new provider session before stopping the old one
- Log (and swallow) stop-session failures for superseded sessions
- Add regression test ensuring failed restart does not stop the active session
---
 .../Layers/ProviderCommandReactor.test.ts     | 58 +++++++++++++++++++
 .../Layers/ProviderCommandReactor.ts          | 10 +++-
 2 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts b/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
index eba9836a3c503e496b67fc500495d21abf75da07..6bbf951b7eafe67c8543d6aa908b02f0f684408f 100644
--- a/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
+++ b/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
@@ -304,6 +304,64 @@ describe("ProviderCommandReactor", () => {
     expect(thread?.session?.sandboxMode).toBe("workspace-write");
   });
 
+  it("does not stop the active session when restart fails before rebind", async () => {
+    const harness = await createHarness();
+    const now = new Date().toISOString();
+
+    await Effect.runPromise(
+      harness.engine.dispatch({
+        type: "thread.turn.start",
+        commandId: CommandId.makeUnsafe("cmd-turn-start-restart-failure-1"),
+        threadId: ThreadId.makeUnsafe("thread-1"),
+        message: {
+          messageId: asMessageId("user-message-restart-failure-1"),
+          role: "user",
+          text: "first",
+          attachments: [],
+        },
+        approvalPolicy: "never",
+        sandboxMode: "danger-full-access",
+        createdAt: now,
+      }),
+    );
+
+    await waitFor(() => harness.startSession.mock.calls.length === 1);
+    await waitFor(() => harness.sendTurn.mock.calls.length === 1);
+
+    harness.startSession.mockImplementationOnce((_: unknown, __: unknown) =>
+      Effect.fail(new Error("simulated restart failure")) as never,
+    );
+
+    await Effect.runPromise(
+      harness.engine.dispatch({
+        type: "thread.turn.start",
+        commandId: CommandId.makeUnsafe("cmd-turn-start-restart-failure-2"),
+        threadId: ThreadId.makeUnsafe("thread-1"),
+        message: {
+          messageId: asMessageId("user-message-restart-failure-2"),
+          role: "user",
+          text: "second",
+          attachments: [],
+        },
+        approvalPolicy: "on-request",
+        sandboxMode: "workspace-write",
+        createdAt: now,
+      }),
+    );
+
+    await waitFor(() => harness.startSession.mock.calls.length === 2);
+    await Effect.runPromise(Effect.sleep("30 millis"));
+
+    expect(harness.stopSession.mock.calls.length).toBe(0);
+    expect(harness.sendTurn.mock.calls.length).toBe(1);
+
+    const readModel = await Effect.runPromise(harness.engine.getReadModel());
+    const thread = readModel.threads.find((entry) => entry.id === ThreadId.makeUnsafe("thread-1"));
+    expect(thread?.session?.providerSessionId).toBe("sess-1");
+    expect(thread?.session?.approvalPolicy).toBe("never");
+    expect(thread?.session?.sandboxMode).toBe("danger-full-access");
+  });
+
   it("reacts to thread.turn.interrupt-requested by calling provider interrupt", async () => {
     const harness = await createHarness();
     const now = new Date().toISOString();
diff --git a/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts b/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts
index 3ae4dc99b5f59695da16e22a2e656d67f428e386..1a206ff646150175caa9be49dce7001992e47aeb 100644
--- a/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts
+++ b/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts
@@ -198,9 +198,17 @@ const make = Effect.gen(function* () {
         return existingSessionId;
       }
 
-      yield* providerService.stopSession({ sessionId: existingSessionId });
       const restartedSession = yield* startProviderSession(thread.session?.providerThreadId ?? null);
       yield* bindSessionToThread(restartedSession);
+      yield* providerService.stopSession({ sessionId: existingSessionId }).pipe(
+        Effect.catchCause((cause) =>
+          Effect.logWarning("provider command reactor failed to stop superseded provider session", {
+            threadId,
+            sessionId: existingSessionId,
+            cause: Cause.pretty(cause),
+          }),
+        ),
+      );
       return restartedSession.sessionId;
     }
 
-- 
2.54.0