diff --git a/packages/server/src/server/session.ts b/packages/server/src/server/session.ts
index 9982ae2fc..813cf0e4d 100644
--- a/packages/server/src/server/session.ts
+++ b/packages/server/src/server/session.ts
@@ -257,6 +257,17 @@ export function resolveCreateAgentTitles(options: {
   };
 }
 
+export function resolveWaitForFinishError(options: {
+  status: "permission" | "error" | "idle";
+  final: AgentSnapshotPayload | null;
+}): string | null {
+  if (options.status !== "error") {
+    return null;
+  }
+  const message = options.final?.lastError;
+  return typeof message === "string" && message.trim().length > 0 ? message : "Agent failed";
+}
+
 type ProcessingPhase = "idle" | "transcribing";
 
 type WorkspaceGitWatchTarget = {
@@ -6569,9 +6580,10 @@ export class Session {
           : record.lastStatus === "error"
             ? "error"
             : "idle";
+      const error = resolveWaitForFinishError({ status, final });
       this.emit({
         type: "wait_for_finish_response",
-        payload: { requestId, status, final, error: null, lastMessage: null },
+        payload: { requestId, status, final, error, lastMessage: null },
       });
       return;
     }
@@ -6598,9 +6610,11 @@ export class Session {
         : result.status === "error"
           ? "error"
           : "idle";
+      const error = resolveWaitForFinishError({ status, final });
+
       this.emit({
         type: "wait_for_finish_response",
-        payload: { requestId, status, final, error: null, lastMessage: result.lastMessage },
+        payload: { requestId, status, final, error, lastMessage: result.lastMessage },
       });
     } catch (error) {
       const isAbort =
diff --git a/packages/server/src/server/session.wait-for-finish.test.ts b/packages/server/src/server/session.wait-for-finish.test.ts
new file mode 100644
index 000000000..d84a5c1c8
--- /dev/null
+++ b/packages/server/src/server/session.wait-for-finish.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, test } from "vitest";
+
+import { resolveWaitForFinishError } from "./session.js";
+
+describe("resolveWaitForFinishError", () => {
+  test("returns the agent error when the wait result is an error", () => {
+    expect(
+      resolveWaitForFinishError({
+        status: "error",
+        final: { lastError: "invalid_json_schema" } as any,
+      }),
+    ).toBe("invalid_json_schema");
+  });
+
+  test("returns a generic fallback when the agent ended in error without a message", () => {
+    expect(
+      resolveWaitForFinishError({
+        status: "error",
+        final: {} as any,
+      }),
+    ).toBe("Agent failed");
+  });
+
+  test("returns null for non-error wait results", () => {
+    expect(
+      resolveWaitForFinishError({
+        status: "idle",
+        final: { lastError: "should not surface" } as any,
+      }),
+    ).toBeNull();
+  });
+});