fix(threads): Keep active-turn runtime errors from ending sessions

apps/server/src/codexAppServerManager.test.ts

@@ -207,6 +207,42 @@ describe("classifyCodexStderrLine", () => {
   });
 });
 
+describe("process stderr events", () => {
+  it("emits classified stderr lines as notifications", () => {
+    const manager = new CodexAppServerManager();
+    const emitEvent = vi
+      .spyOn(manager as unknown as { emitEvent: (...args: unknown[]) => void }, "emitEvent")
+      .mockImplementation(() => {});
+
+    (
+      manager as unknown as {
+        emitNotificationEvent: (
+          context: { session: { threadId: ThreadId } },
+          method: string,
+          message: string,
+        ) => void;
+      }
+    ).emitNotificationEvent(
+      {
+        session: {
+          threadId: asThreadId("thread-1"),
+        },
+      },
+      "process/stderr",
+      "fatal: permission denied",
+    );
+
+    expect(emitEvent).toHaveBeenCalledWith(
+      expect.objectContaining({
+        kind: "notification",
+        method: "process/stderr",
+        threadId: "thread-1",
+        message: "fatal: permission denied",
+      }),
+    );
+  });
+});
+
 describe("normalizeCodexModelSlug", () => {
   it("maps 5.3 aliases to gpt-5.3-codex", () => {
     expect(normalizeCodexModelSlug("5.3")).toBe("gpt-5.3-codex");

apps/server/src/codexAppServerManager.ts

@@ -1046,7 +1046,7 @@ export class CodexAppServerManager extends EventEmitter<CodexAppServerManagerEve
           continue;
         }
 
-        this.emitErrorEvent(context, "process/stderr", classified.message);
+        this.emitNotificationEvent(context, "process/stderr", classified.message);
       }
     });
 
@@ -1354,6 +1354,22 @@ export class CodexAppServerManager extends EventEmitter<CodexAppServerManagerEve
     });
   }
 
+  private emitNotificationEvent(
+    context: CodexSessionContext,
+    method: string,
+    message: string,
+  ): void {
+    this.emitEvent({
+      id: EventId.makeUnsafe(randomUUID()),
+      kind: "notification",
+      provider: "codex",
+      threadId: context.session.threadId,
+      createdAt: new Date().toISOString(),
+      method,
+      message,
+    });
+  }
+
   private emitEvent(event: ProviderEvent): void {
     this.emit("event", event);
   }

apps/server/src/provider/Layers/CodexAdapter.test.ts

@@ -474,6 +474,40 @@ lifecycleLayer("CodexAdapterLive lifecycle", (it) => {
     }),
   );
 
+  it.effect("maps process stderr notifications to runtime.warning", () =>
+    Effect.gen(function* () {
+      const adapter = yield* CodexAdapter;
+      const firstEventFiber = yield* Stream.runHead(adapter.streamEvents).pipe(Effect.forkChild);
+
+      lifecycleManager.emit("event", {
+        id: asEventId("evt-process-stderr"),
+        kind: "notification",
+        provider: "codex",
+        threadId: asThreadId("thread-1"),
+        createdAt: new Date().toISOString(),
+        method: "process/stderr",
+        turnId: asTurnId("turn-1"),
+        message: "The filename or extension is too long. (os error 206)",
+      } satisfies ProviderEvent);
+
+      const firstEvent = yield* Fiber.join(firstEventFiber);
+
+      assert.equal(firstEvent._tag, "Some");
+      if (firstEvent._tag !== "Some") {
+        return;
+      }
+      assert.equal(firstEvent.value.type, "runtime.warning");
+      if (firstEvent.value.type !== "runtime.warning") {
+        return;
+      }
+      assert.equal(firstEvent.value.turnId, "turn-1");
+      assert.equal(
+        firstEvent.value.payload.message,
+        "The filename or extension is too long. (os error 206)",
+      );
+    }),
+  );
+
   it.effect("preserves request type when mapping serverRequest/resolved", () =>
     Effect.gen(function* () {
       const adapter = yield* CodexAdapter;

apps/server/src/provider/Layers/CodexAdapter.ts

@@ -1267,6 +1267,19 @@ function mapToRuntimeEvents(
     ];
   }
 
+  if (event.method === "process/stderr") {
+    return [
+      {
+        type: "runtime.warning",
+        ...runtimeEventBase(event, canonicalThreadId),
+        payload: {
+          message: event.message ?? "Codex process stderr",
+          ...(event.payload !== undefined ? { detail: event.payload } : {}),
+        },
+      },
+    ];
+  }
+
   if (event.method === "windows/worldWritableWarning") {
     return [
       {