fix: replace stale codex threads

src/backend/codex-stdio.ts

@@ -453,7 +453,8 @@ async function runCodexStdioTurnWithSession(options: CodexStdioTurnOptions, sess
       } catch (error) {
         const failure = normalizeFailure(error);
         if (!isMissingRolloutThreadResumeFailure(failure)) throw error;
-        throw threadResumeFailure(options.threadId, failure);
+        emitEvent({ type: "backend_status", payload: threadResumeNonResumablePayload(options.threadId, failure) });
+        threadId = await startThread("thread/replacement-start");
       }
     } else {
       threadId = await startThread();
@@ -930,6 +931,18 @@ function threadResumeFailure(threadId: string, error: CodexStdioFailure): CodexS
   );
 }
 
+function threadResumeNonResumablePayload(threadId: string, error: CodexStdioFailure): JsonRecord {
+  return {
+    phase: "thread/resume:non-resumable",
+    requestedThreadId: threadId,
+    originalFailureKind: error.failureKind,
+    originalPhase: error.phase,
+    originalDetails: redactJson(error.details),
+    replacement: "thread/start",
+    valuesPrinted: false,
+  };
+}
+
 function classifyCodexErrorRecord(error: JsonRecord, fallback: FailureKind): FailureKind {
   const parts: string[] = [];
   if (typeof error.message === "string") parts.push(error.message);

src/selftest/cases/30-codex-stdio.ts

@@ -105,18 +105,19 @@ const selfTest: SelfTestCase = async (context) => {
       env: { CODEX_HOME: context.codexHome, AGENTRUN_FAKE_CODEX_MODE: "resume-no-rollout" },
       oneShot: true,
     }) as JsonRecord;
-    assert.equal(staleThreadResult.terminalStatus, "failed", "stale thread resume must fail instead of creating a replacement thread");
-    assert.equal(staleThreadResult.failureKind, "thread-resume-failed", "stale thread resume failure kind");
+    assert.equal(staleThreadResult.terminalStatus, "completed", "stale thread resume should create a replacement thread and continue the turn");
+    assert.equal(staleThreadResult.failureKind, null, "replacement stale thread turn should not expose thread-resume-failed as terminal failure");
     const staleEnvelope = await client.get(`/api/v1/runs/${staleThread.runId}/commands/${staleThread.commandId}/result`) as JsonRecord;
-    assert.equal(staleEnvelope.terminalStatus, "failed");
-    assert.equal(staleEnvelope.failureKind, "thread-resume-failed");
-    assert.equal(staleEnvelope.completed, false);
-    assert.equal((staleEnvelope.sessionRef as JsonRecord).threadId, "thread_missing_rollout");
+    assert.equal(staleEnvelope.terminalStatus, "completed");
+    assert.equal(staleEnvelope.failureKind, null);
+    assert.equal(staleEnvelope.completed, true);
+    assert.equal((staleEnvelope.sessionRef as JsonRecord).threadId, "thread_selftest_1");
     const staleEvents = await client.get(`/api/v1/runs/${staleThread.runId}/events?afterSeq=0&limit=100`) as { items?: Array<{ type: string; payload: unknown }> };
     const stalePhases = (staleEvents.items ?? []).filter((event) => event.type === "backend_status").map((event) => String(eventPayload(event).phase ?? ""));
-    assert.equal(stalePhases.some((phase) => phase.startsWith("thread/start")), false, "stale resume must not start a replacement thread");
+    assert.equal(staleEvents.items?.some((event) => event.type === "backend_status" && eventPayload(event).phase === "thread/resume:non-resumable"), true, "stale resume must be visible as non-resumable before replacement");
+    assert.equal(stalePhases.some((phase) => phase === "thread/replacement-start:completed"), true, "stale resume must start a replacement thread");
     assert.equal(staleEvents.items?.some((event) => event.type === "backend_status" && eventPayload(event).phase === "thread/resume:completed"), false, "stale resume must not be reported as a successful resume");
-    assert.equal(staleEvents.items?.some((event) => event.type === "error" && eventPayload(event).failureKind === "thread-resume-failed"), true, "stale resume failure must be visible as an error event");
+    assert.equal(staleEvents.items?.some((event) => event.type === "error" && eventPayload(event).failureKind === "thread-resume-failed"), false, "replacement stale resume must not surface terminal thread-resume-failed error");
     assertNoSecretLeak({ staleThreadResult, staleEnvelope, staleEvents });
 
     const live = await createRunWithCommand(client, context, "hello live events", "selftest-live-tool-events", 15_000);
@@ -185,7 +186,7 @@ const selfTest: SelfTestCase = async (context) => {
     await runSecretFailureCase({ client, managerUrl: server.baseUrl, context });
     await runSpawnFailureCase({ client, managerUrl: server.baseUrl, context });
 
-    return { name: "codex-stdio", tests: ["runner-lease-heartbeat", "codex-stdio-fake-turn", "codex-stdio-projected-writable-home", "codex-stdio-deepseek-profile-fake-turn", "codex-stdio-minimax-m3-profile-fake-turn", "codex-stdio-deepseek-missing-secret-no-fallback", "codex-stdio-minimax-m3-missing-secret-no-fallback", "codex-stdio-config-model-authoritative", "codex-stdio-explicit-model-forwarded", "codex-stdio-final-agent-message-only", "codex-stdio-stale-thread-resume-fails", "codex-stdio-live-tool-events", "codex-stdio-noisy-reasoning-suppression", "codex-stdio-missing-turn-result", "codex-stdio-provider-auth-failed", "codex-stdio-provider-rate-limited", "codex-stdio-provider-invalid-tool-call", "codex-stdio-provider-503-rpc-error", "codex-stdio-provider-503-terminal", "codex-stdio-provider-503-retry-event", "codex-stdio-invalid-json", "codex-stdio-timeout", "codex-stdio-secret-unavailable", "codex-stdio-spawn-failure"] };
+    return { name: "codex-stdio", tests: ["runner-lease-heartbeat", "codex-stdio-fake-turn", "codex-stdio-projected-writable-home", "codex-stdio-deepseek-profile-fake-turn", "codex-stdio-minimax-m3-profile-fake-turn", "codex-stdio-deepseek-missing-secret-no-fallback", "codex-stdio-minimax-m3-missing-secret-no-fallback", "codex-stdio-config-model-authoritative", "codex-stdio-explicit-model-forwarded", "codex-stdio-final-agent-message-only", "codex-stdio-stale-thread-replacement", "codex-stdio-live-tool-events", "codex-stdio-noisy-reasoning-suppression", "codex-stdio-missing-turn-result", "codex-stdio-provider-auth-failed", "codex-stdio-provider-rate-limited", "codex-stdio-provider-invalid-tool-call", "codex-stdio-provider-503-rpc-error", "codex-stdio-provider-503-terminal", "codex-stdio-provider-503-retry-event", "codex-stdio-invalid-json", "codex-stdio-timeout", "codex-stdio-secret-unavailable", "codex-stdio-spawn-failure"] };
   } finally {
     await new Promise<void>((resolve) => server.server.close(() => resolve()));
   }