fix(server): resume with last live mode, not creation-time mode (#5140)

* fix(server): resume with last live mode, not creation-time mode

Provider-initiated mode switches (ACP current_mode_update, in-session
commands like /bypass, permission-driven plan->acceptEdits transitions)
update currentModeId/lastModeId but never reach config.modeId. On
resume, buildConfigOverrides restored the stale creation-time mode and
applyConfiguredOverrides pushed it back via set_mode — silently
downgrading the session (e.g. bypass -> acceptEdits after restart).

- buildConfigOverrides + buildStoredAgentConfig prefer lastModeId
  (the last observed live mode) over config.modeId
- applyObservedMode syncs config.modeId on every provider-reported
  mode change (mode_changed, model_changed runtimeInfo, and the
  refreshSessionState poll) so in-memory reloadAgentSession carries
  the live mode as well

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* test(server): assert config.modeId sync on mode_changed/model_changed events

Extends the config-drift stream test with a registry so both the
in-memory agent.config.modeId and the persisted record.config.modeId
are verified — covering the event paths Greptile flagged as untested.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

packages/server/src/server/agent/agent-manager.test.ts

@@ -5034,6 +5034,7 @@ test("setAgentThinkingOption surfaces a failed state read and keeps the previous
 
 test("session config drift events update state through the stream channel", async () => {
   const workdir = mkdtempSync(join(tmpdir(), "agent-manager-session-config-events-"));
+  const storage = new AgentStorage(join(workdir, "agents"), logger);
   let capturedSession: TestAgentSession | null = null;
   class ConfigEventClient extends TestAgentClient {
     override async createSession(config: AgentSessionConfig): Promise<AgentSession> {
@@ -5046,6 +5047,7 @@ test("session config drift events update state through the stream channel", asyn
     clients: {
       codex: new ConfigEventClient(),
     },
+    registry: storage,
     logger,
     idFactory: () => "00000000-0000-4000-8000-000000000133",
   });
@@ -5100,6 +5102,7 @@ test("session config drift events update state through the stream channel", asyn
 
   const agent = manager.getAgent(snapshot.id);
   expect(agent?.currentModeId).toBe("build");
+  expect(agent?.config.modeId).toBe("build");
   expect(agent?.config.thinkingOptionId).toBe("high");
   expect(agent?.availableModes).toEqual([
     { id: "plan", label: "Plan" },
@@ -5111,6 +5114,10 @@ test("session config drift events update state through the stream channel", asyn
     thinkingOptionId: "high",
   });
   expect(streams.map((event) => event.type)).toEqual([]);
+
+  const persisted = await storage.get(snapshot.id);
+  expect(persisted?.lastModeId).toBe("build");
+  expect(persisted?.config?.modeId).toBe("build");
 });
 
 test("setLabels merges and persists labels", async () => {
@@ -9287,6 +9294,7 @@ test("respondToPermission updates currentModeId after plan approval", async () =
   class PlanModeTestClient implements AgentClient {
     readonly provider = "codex" as const;
     readonly capabilities = TEST_CAPABILITIES;
+    resumedModeId: string | null | undefined;
 
     async isAvailable(): Promise<boolean> {
       return true;
@@ -9296,14 +9304,19 @@ test("respondToPermission updates currentModeId after plan approval", async () =
       return new PlanModeTestSession();
     }
 
-    async resumeSession(): Promise<AgentSession> {
+    async resumeSession(
+      _handle: AgentPersistenceHandle,
+      overrides?: Partial<AgentSessionConfig>,
+    ): Promise<AgentSession> {
+      this.resumedModeId = overrides?.modeId;
       return new PlanModeTestSession();
     }
   }
 
+  const client = new PlanModeTestClient();
   const manager = new AgentManager({
     clients: {
-      codex: new PlanModeTestClient(),
+      codex: client,
     },
     registry: storage,
     logger,
@@ -9347,6 +9360,13 @@ test("respondToPermission updates currentModeId after plan approval", async () =
   await manager.flush();
   const persisted = await storage.get(snapshot.id);
   expect(persisted?.lastModeId).toBe("acceptEdits");
+
+  // The provider-managed switch must also reach config.modeId — otherwise a
+  // reload resumes the session with the stale creation-time mode ("plan").
+  expect(persisted?.config?.modeId).toBe("acceptEdits");
+  const reloaded = await manager.reloadAgentSession(snapshot.id);
+  expect(reloaded.config.modeId).toBe("acceptEdits");
+  expect(client.resumedModeId).toBe("acceptEdits");
 });
 
 test("respondToPermission refreshes features and runtime info after provider-managed plan approval", async () => {

packages/server/src/server/agent/agent-manager.ts

@@ -190,10 +190,13 @@ function buildStoredAgentConfig(record: StoredAgentRecord): AgentSessionConfig {
     provider: record.provider,
     cwd: record.cwd,
   };
+  // lastModeId is the last live mode — it also covers provider-side switches
+  // that never reach record.config.modeId.
+  const modeId = record.lastModeId ?? record.config?.modeId;
+  if (modeId != null) config.modeId = modeId;
   if (!record.config) {
     return config;
   }
-  if (record.config.modeId != null) config.modeId = record.config.modeId;
   if (record.config.model != null) config.model = record.config.model;
   if (record.config.thinkingOptionId != null) {
     config.thinkingOptionId = record.config.thinkingOptionId;
@@ -3914,6 +3917,19 @@ export class AgentManager {
     return this.registry;
   }
 
+  /**
+   * Provider-side mode switches (ACP current_mode_update, in-session
+   * commands, permission-driven transitions) must land in config.modeId too —
+   * reloadAgentSession and the persisted record derive the resumed session's
+   * mode from it, so leaving it stale silently downgrades the mode on resume.
+   */
+  private applyObservedMode(agent: ActiveManagedAgent, modeId: string | null): void {
+    agent.currentModeId = modeId;
+    if (modeId != null) {
+      agent.config.modeId = modeId;
+    }
+  }
+
   private async refreshSessionState(
     agent: ActiveManagedAgent,
     options?: { emit?: boolean },
@@ -3926,7 +3942,7 @@ export class AgentManager {
     }
 
     try {
-      agent.currentModeId = await agent.session.getCurrentMode();
+      this.applyObservedMode(agent, await agent.session.getCurrentMode());
     } catch {
       agent.currentModeId = null;
     }
@@ -4306,7 +4322,7 @@ export class AgentManager {
         this.emitState(agent);
         return undefined;
       case "mode_changed":
-        agent.currentModeId = event.currentModeId;
+        this.applyObservedMode(agent, event.currentModeId);
         agent.availableModes = event.availableModes;
         if (agent.runtimeInfo) {
           agent.runtimeInfo = { ...agent.runtimeInfo, modeId: event.currentModeId };
@@ -4322,7 +4338,7 @@ export class AgentManager {
             agent.cwd,
           );
         }
-        agent.currentModeId = event.runtimeInfo.modeId ?? agent.currentModeId;
+        this.applyObservedMode(agent, event.runtimeInfo.modeId ?? agent.currentModeId);
         flags.shouldDispatchEvent = false;
         this.emitState(agent);
         return undefined;

packages/server/src/server/persistence-hooks.test.ts

@@ -27,9 +27,28 @@ function createRecord(overrides?: Partial<StoredAgentRecord>): StoredAgentRecord
 }
 
 describe("persistence hooks", () => {
+  test("buildConfigOverrides prefers the last live mode over the creation-time mode", () => {
+    const record = createRecord({
+      lastModeId: "bypass",
+      config: { modeId: "acceptEdits" },
+    });
+
+    expect(buildConfigOverrides(record).modeId).toBe("bypass");
+  });
+
+  test("buildConfigOverrides falls back to the configured mode when no live mode was recorded", () => {
+    const record = createRecord({
+      lastModeId: null,
+      config: { modeId: "acceptEdits" },
+    });
+
+    expect(buildConfigOverrides(record).modeId).toBe("acceptEdits");
+  });
+
   test("buildConfigOverrides preserves the complete private launch config", () => {
     const record = createRecord({
       title: "Voice agent (current)",
+      lastModeId: "default",
       config: {
         modeId: "default",
         model: "gpt-5.4-mini",
@@ -79,6 +98,7 @@ describe("persistence hooks", () => {
     const record = createRecord({
       provider: "codex",
       title: "Renamed title",
+      lastModeId: null,
       config: {
         model: "gpt-5.4-mini",
         systemPrompt: "Confirm and speak first.",

packages/server/src/server/persistence-hooks.ts

@@ -67,7 +67,10 @@ export function buildConfigOverrides(record: StoredAgentRecord): Partial<AgentSe
   return stripInternalPaseoMcpServer({
     provider: record.provider,
     cwd: record.cwd,
-    modeId: record.config?.modeId ?? undefined,
+    // lastModeId is the last live mode — it also covers provider-side switches
+    // (ACP current_mode_update, in-session commands) that never reach
+    // record.config.modeId.
+    modeId: record.lastModeId ?? record.config?.modeId ?? undefined,
     model: record.config?.model ?? undefined,
     thinkingOptionId: record.config?.thinkingOptionId ?? undefined,
     featureValues: record.config?.featureValues ?? undefined,