fix(acp): propagate setSessionMode gateway errors to client (#41185)

* fix(acp): propagate setSessionMode gateway errors to client

* fix: add changelog entry for ACP setSessionMode propagation (#41185) (thanks @pejmanjohn)

---------

Co-authored-by: Pejman Pour-Moezzi <481729+pejmanjohn@users.noreply.github.com>
Co-authored-by: Onur <onur@textcortex.com>

CHANGELOG.md

@@ -17,6 +17,7 @@ Docs: https://docs.openclaw.ai
 - Agents/embedded runner: bound compaction retry waiting and drain embedded runs during SIGUSR1 restart so session lanes recover instead of staying blocked behind compaction. (#40324) thanks @cgdusek.
 - ACP/sessions.patch: allow `spawnedBy` and `spawnDepth` lineage fields on ACP session keys so `sessions_spawn` with `runtime: "acp"` no longer fails during child-session setup. Fixes #40971. (#40995) thanks @xaeon2026.
 - ACP/stop reason mapping: resolve gateway chat `state: "error"` completions as ACP `end_turn` instead of `refusal` so transient backend failures are not surfaced as deliberate refusals. (#41187) thanks @pejmanjohn.
+- ACP/setSessionMode: propagate gateway `sessions.patch` failures back to ACP clients so rejected mode changes no longer return silent success. (#41185) thanks @pejmanjohn.
 
 ## 2026.3.8
 

src/acp/translator.set-session-mode.test.ts

@@ -0,0 +1,61 @@
+import type { SetSessionModeRequest } from "@agentclientprotocol/sdk";
+import { describe, expect, it, vi } from "vitest";
+import type { GatewayClient } from "../gateway/client.js";
+import { createInMemorySessionStore } from "./session.js";
+import { AcpGatewayAgent } from "./translator.js";
+import { createAcpConnection, createAcpGateway } from "./translator.test-helpers.js";
+
+function createSetSessionModeRequest(modeId: string): SetSessionModeRequest {
+  return {
+    sessionId: "session-1",
+    modeId,
+  } as unknown as SetSessionModeRequest;
+}
+
+function createAgentWithSession(request: GatewayClient["request"]) {
+  const sessionStore = createInMemorySessionStore();
+  sessionStore.createSession({
+    sessionId: "session-1",
+    sessionKey: "agent:main:main",
+    cwd: "/tmp",
+  });
+  return new AcpGatewayAgent(createAcpConnection(), createAcpGateway(request), {
+    sessionStore,
+  });
+}
+
+describe("acp setSessionMode", () => {
+  it("setSessionMode propagates gateway error", async () => {
+    const request = vi.fn(async () => {
+      throw new Error("gateway rejected mode change");
+    }) as GatewayClient["request"];
+    const agent = createAgentWithSession(request);
+
+    await expect(agent.setSessionMode(createSetSessionModeRequest("high"))).rejects.toThrow(
+      "gateway rejected mode change",
+    );
+    expect(request).toHaveBeenCalledWith("sessions.patch", {
+      key: "agent:main:main",
+      thinkingLevel: "high",
+    });
+  });
+
+  it("setSessionMode succeeds when gateway accepts", async () => {
+    const request = vi.fn(async () => ({ ok: true })) as GatewayClient["request"];
+    const agent = createAgentWithSession(request);
+
+    await expect(agent.setSessionMode(createSetSessionModeRequest("low"))).resolves.toEqual({});
+    expect(request).toHaveBeenCalledWith("sessions.patch", {
+      key: "agent:main:main",
+      thinkingLevel: "low",
+    });
+  });
+
+  it("setSessionMode returns early for empty modeId", async () => {
+    const request = vi.fn(async () => ({ ok: true })) as GatewayClient["request"];
+    const agent = createAgentWithSession(request);
+
+    await expect(agent.setSessionMode(createSetSessionModeRequest(""))).resolves.toEqual({});
+    expect(request).not.toHaveBeenCalled();
+  });
+});

src/acp/translator.ts

@@ -256,6 +256,7 @@ export class AcpGatewayAgent implements Agent {
       this.log(`setSessionMode: ${session.sessionId} -> ${params.modeId}`);
     } catch (err) {
       this.log(`setSessionMode error: ${String(err)}`);
+      throw err;
     }
     return {};
   }