diff --git a/src/main/worker/runtime/index.ts b/src/main/worker/runtime/index.ts
index f78f81b5..6c1da392 100644
--- a/src/main/worker/runtime/index.ts
+++ b/src/main/worker/runtime/index.ts
@@ -202,10 +202,13 @@ export class WorkerRunner {
         });
 
         if (event.type === "message_end" && event.message) {
-          await rpc.invoke(job.runId, "persistMessage", {
+          const persistResponse = await rpc.invoke(job.runId, "persistMessage", {
             taskSessionId: job.taskSessionId,
             message: event.message,
           });
+          if (!persistResponse.ok) {
+            throw new Error(`persistMessage RPC failed: ${persistResponse.error}`);
+          }
           const maybeAssistant = event.message as {
             role?: string;
             stopReason?: string;
diff --git a/tests/unit/worker-runner-persistence.test.ts b/tests/unit/worker-runner-persistence.test.ts
new file mode 100644
index 00000000..5dbf7e9e
--- /dev/null
+++ b/tests/unit/worker-runner-persistence.test.ts
@@ -0,0 +1,154 @@
+import type { AgentMessage } from "@mariozechner/pi-agent-core";
+import { describe, expect, it, vi } from "vitest";
+import type { ChildMessage, RunJob } from "../../src/main/worker/runtime/helpers";
+import type { WorkerRpcClient } from "../../src/main/worker/entry/rpc";
+
+const createPiAgentMock = vi.fn();
+
+vi.mock("../../src/main/model-resolver", () => ({
+  resolveModel: vi.fn(() => ({
+    id: "model-1",
+    name: "Model 1",
+    api: "openai-responses",
+    provider: "openai",
+    baseUrl: "https://example.invalid",
+    reasoning: false,
+    input: ["text"],
+    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+    contextWindow: 8192,
+    maxTokens: 2048,
+  })),
+  resolveExtraStreamHeaders: vi.fn(() => undefined),
+}));
+
+vi.mock("../../src/main/worker/runtime/run-tools", () => ({
+  createRunScopedCodingTools: vi.fn(() => []),
+  mergeRunEnvs: vi.fn((base: Record<string, string>, extra: Record<string, string>) => ({ ...base, ...extra })),
+}));
+
+vi.mock("../../src/main/worker/runtime/pi-agent-factory", () => ({
+  createPiAgent: createPiAgentMock,
+  resolveThinkingLevel: vi.fn(() => "off"),
+}));
+
+async function importWorkerRunner() {
+  const module = await import("../../src/main/worker/runtime");
+  return module.WorkerRunner;
+}
+
+function createJob(): RunJob {
+  return {
+    runId: "11111111-1111-4111-8111-111111111111",
+    companyId: "company-1",
+    taskId: "task-1",
+    agentId: "agent-1",
+    agentName: "Agent One",
+    connectorId: "openai",
+    workspaceId: null,
+    workspacePath: null,
+    workspaceMode: "none",
+    model: "model-1",
+    thinkingEffort: null,
+    env: {},
+    systemPrompt: "system",
+    trigger: "manual",
+    taskSessionId: "session-1",
+    executionMode: "ai_ceo",
+    initialUserTurn: "Start.",
+    internalTools: [],
+  };
+}
+
+function assistantMessage(): AgentMessage {
+  return {
+    role: "assistant",
+    content: [{ type: "text", text: "done" }],
+    api: "openai-responses",
+    provider: "openai",
+    model: "model-1",
+    timestamp: 1,
+    stopReason: "stop",
+    usage: {
+      input: 10,
+      output: 5,
+      cacheRead: 0,
+      cacheWrite: 0,
+      totalTokens: 15,
+      cost: {
+        input: 0,
+        output: 0,
+        cacheRead: 0,
+        cacheWrite: 0,
+        total: 0.01,
+      },
+    },
+  };
+}
+
+function createAgentEmitting(message: AgentMessage) {
+  let listener: ((event: { type: string; message?: AgentMessage }, signal: AbortSignal) => Promise<void>) | null = null;
+  return {
+    abort: vi.fn(),
+    steer: vi.fn(),
+    subscribe: vi.fn((nextListener) => {
+      listener = nextListener;
+      return vi.fn();
+    }),
+    prompt: vi.fn(async () => {
+      if (!listener) throw new Error("Agent subscribed after prompt.");
+      await listener({ type: "message_end", message }, new AbortController().signal);
+    }),
+  };
+}
+
+function createRpcWithPersistenceFailure() {
+  return {
+    invoke: vi.fn(async (_runId: string, method: string) => {
+      if (method === "prepareRun") {
+        return {
+          ok: true,
+          result: {
+            provider: "openai",
+            apiKey: "test-key",
+            extraEnv: {},
+            priorMessages: [],
+          },
+        };
+      }
+      if (method === "persistMessage") {
+        return { ok: false, error: "append failed" };
+      }
+      throw new Error(`Unexpected RPC method ${method}.`);
+    }),
+  } as unknown as WorkerRpcClient & { invoke: ReturnType<typeof vi.fn> };
+}
+
+describe("WorkerRunner message persistence", () => {
+  it("fails the run when persisting an emitted message fails", async () => {
+    createPiAgentMock.mockReturnValue(createAgentEmitting(assistantMessage()));
+    const rpc = createRpcWithPersistenceFailure();
+    const messages: ChildMessage[] = [];
+    const WorkerRunner = await importWorkerRunner();
+    const runner = new WorkerRunner({
+      post: (message) => messages.push(message),
+      rpc,
+      isCancelled: () => false,
+    });
+
+    await runner.run(createJob());
+
+    const finished = messages.find((message): message is Extract<ChildMessage, { type: "run-finished" }> => {
+      return message.type === "run-finished";
+    });
+
+    expect(rpc.invoke).toHaveBeenCalledWith("11111111-1111-4111-8111-111111111111", "persistMessage", {
+      taskSessionId: "session-1",
+      message: assistantMessage(),
+    });
+    expect(finished).toMatchObject({
+      type: "run-finished",
+      status: "failed",
+      errorMessage: "persistMessage RPC failed: append failed",
+    });
+  });
+});