diff --git a/packages/runtime/CHANGELOG.md b/packages/runtime/CHANGELOG.md
index 5d47b01f..1e1fb8a1 100644
--- a/packages/runtime/CHANGELOG.md
+++ b/packages/runtime/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Treat Relayfile writebacks that time out without receipts as first-class `WritebackError`s from the runtime client helpers.
+
 ## [4.1.5] - 2026-06-18
 
 ### Dependencies
diff --git a/packages/runtime/src/clients/index.test.ts b/packages/runtime/src/clients/index.test.ts
new file mode 100644
index 00000000..debe63df
--- /dev/null
+++ b/packages/runtime/src/clients/index.test.ts
@@ -0,0 +1,92 @@
+import assert from 'node:assert/strict';
+import { mkdir, mkdtemp, readFile, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import test from 'node:test';
+import {
+  WorkforceIntegrationError,
+  WritebackError,
+  normalizeWritebackStatus,
+  writeJsonFile
+} from './index.js';
+
+test('writeJsonFile returns successful writes with receipts', async () => {
+  const root = await mkdtemp(path.join(tmpdir(), 'workforce-writeback-ok-'));
+  const relayPath = '/slack/channels/C123/messages/msg.json';
+  const absolutePath = path.join(root, relayPath.slice(1));
+
+  const pending = writeJsonFile(
+    { relayfileMountRoot: root, writebackTimeoutMs: 1_000, writebackPollMs: 10 },
+    'slack',
+    'postMessage',
+    relayPath,
+    { text: 'hello' }
+  );
+
+  await waitForDraft(absolutePath);
+  await writeFile(
+    absolutePath,
+    `${JSON.stringify({ created: '2026-06-18T18:00:00.000Z', id: 'msg-1', path: relayPath })}\n`,
+    'utf8'
+  );
+
+  const result = await pending;
+  assert.equal(result.path, relayPath);
+  assert.equal(result.receipt?.id, 'msg-1');
+  assert.equal(normalizeWritebackStatus(result).state, 'succeeded');
+});
+
+test('writeJsonFile treats missing receipts as first-class writeback errors', async () => {
+  const root = await mkdtemp(path.join(tmpdir(), 'workforce-writeback-no-receipt-'));
+
+  await assert.rejects(
+    () =>
+      writeJsonFile(
+        { relayfileMountRoot: root, writebackTimeoutMs: 1, writebackPollMs: 1 },
+        'slack',
+        'postMessage',
+        '/slack/channels/C123/messages/msg.json',
+        { text: 'hello' }
+      ),
+    (error: unknown) => {
+      assert(error instanceof WritebackError);
+      assert(error instanceof WorkforceIntegrationError);
+      assert.equal((error as { state?: unknown }).state, 'no_receipt');
+      assert.equal((error as { path?: unknown }).path, '/slack/channels/C123/messages/msg.json');
+      return true;
+    }
+  );
+});
+
+test('writeJsonFile preserves explicit fire-and-forget writebacks', async () => {
+  const root = await mkdtemp(path.join(tmpdir(), 'workforce-writeback-fire-and-forget-'));
+  const relayPath = '/slack/channels/C123/messages/msg.json';
+
+  const result = await writeJsonFile(
+    { relayfileMountRoot: root, writebackTimeoutMs: 0 },
+    'slack',
+    'postMessage',
+    relayPath,
+    { text: 'hello' }
+  );
+
+  assert.equal(result.path, relayPath);
+  assert.equal(result.receipt, undefined);
+  assert.deepEqual(JSON.parse(await readFile(path.join(root, relayPath.slice(1)), 'utf8')), {
+    text: 'hello'
+  });
+});
+
+async function waitForDraft(filePath: string): Promise<void> {
+  await mkdir(path.dirname(filePath), { recursive: true });
+  const deadline = Date.now() + 1_000;
+  do {
+    try {
+      await readFile(filePath, 'utf8');
+      return;
+    } catch {
+      await new Promise((resolve) => setTimeout(resolve, 10));
+    }
+  } while (Date.now() < deadline);
+  throw new Error(`draft was not written: ${filePath}`);
+}
diff --git a/packages/runtime/src/clients/index.ts b/packages/runtime/src/clients/index.ts
index 08c56826..ab54058f 100644
--- a/packages/runtime/src/clients/index.ts
+++ b/packages/runtime/src/clients/index.ts
@@ -1,3 +1,12 @@
+import * as adapterVfsClient from '@relayfile/adapter-core/vfs-client';
+import {
+  writeJsonFile as coreWriteJsonFile,
+  RelayfileWritebackError,
+  type IntegrationClientOptions,
+  type WritebackReceipt,
+  type WritebackResult
+} from '@relayfile/adapter-core/vfs-client';
+
 // Shared VFS-backed transport surface. All provider interactions go through
 // these helpers — no per-provider client code lives in the runtime.
 //
@@ -15,7 +24,6 @@ export {
   readJsonFile,
   readTextFile,
   resolveMountRoot,
-  writeJsonFile,
   RelayfileWritebackError,
   type RelayfileWritebackErrorOptions,
   type IntegrationClientOptions,
@@ -28,3 +36,116 @@ export {
   type WorkforceIntegrationErrorOptions,
   SandboxNotAvailableError
 } from '../errors.js';
+
+export type NormalizedWritebackState =
+  | 'succeeded'
+  | 'no_receipt'
+  | 'validation_failed'
+  | 'readonly_rejected'
+  | 'adapter_error'
+  | 'ok';
+
+export interface NormalizedWritebackStatus {
+  state: NormalizedWritebackState;
+  path: string;
+  op?: 'create' | 'patch' | 'delete';
+  id?: string;
+  error?: string;
+  field?: string;
+  receipt?: WritebackReceipt;
+  timestamp?: string;
+  entry?: unknown;
+}
+
+type AdapterVfsClientExtensions = {
+  normalizeWritebackStatus?: (
+    result?: WritebackResult,
+    entry?: unknown
+  ) => NormalizedWritebackStatus;
+  WritebackError?: new (normalized: NormalizedWritebackStatus) => RelayfileWritebackError &
+    NormalizedWritebackStatus;
+};
+
+class FallbackWritebackError extends RelayfileWritebackError {
+  readonly state: NormalizedWritebackState;
+  readonly path: string;
+  readonly op?: 'create' | 'patch' | 'delete';
+  readonly id?: string;
+  readonly receipt?: WritebackReceipt;
+  readonly error?: string;
+  readonly field?: string;
+  readonly timestamp?: string;
+
+  constructor(normalized: NormalizedWritebackStatus) {
+    super({
+      provider: 'writeback',
+      operation: normalized.state,
+      cause: normalized.error ? new Error(normalized.error) : undefined,
+      retryable: false
+    });
+    this.name = 'WritebackError';
+    this.message = `writeback ${normalized.state} ${normalized.path}${
+      normalized.error ? `: ${normalized.error}` : ''
+    }`;
+    this.state = normalized.state;
+    this.path = normalized.path;
+    this.op = normalized.op;
+    this.id = normalized.id;
+    this.receipt = normalized.receipt;
+    this.error = normalized.error;
+    this.field = normalized.field;
+    this.timestamp = normalized.timestamp;
+  }
+}
+
+const adapterExtensions = adapterVfsClient as AdapterVfsClientExtensions;
+
+export const WritebackError = adapterExtensions.WritebackError ?? FallbackWritebackError;
+
+export function normalizeWritebackStatus(
+  result?: WritebackResult,
+  entry?: unknown
+): NormalizedWritebackStatus {
+  const normalize = adapterExtensions.normalizeWritebackStatus;
+  if (normalize) return normalize(result, entry);
+
+  if (!result?.receipt) {
+    return {
+      state: 'no_receipt',
+      path: result?.path ?? '',
+      error: 'writeback produced no receipt'
+    };
+  }
+
+  const receipt = result.receipt;
+  const id =
+    receipt.id !== undefined
+      ? String(receipt.id)
+      : receipt.created !== undefined
+        ? String(receipt.created)
+        : undefined;
+  return {
+    state: 'succeeded',
+    path: result.path,
+    ...(id ? { id } : {}),
+    receipt
+  };
+}
+
+export async function writeJsonFile(
+  client: IntegrationClientOptions,
+  provider: string,
+  operation: string,
+  relayPath: string,
+  body: unknown
+): Promise<WritebackResult> {
+  const result = await coreWriteJsonFile(client, provider, operation, relayPath, body);
+  const normalized = normalizeWritebackStatus(result);
+  if (normalized.state !== 'succeeded') {
+    if (client.writebackTimeoutMs === 0 && normalized.state === 'no_receipt') {
+      return result;
+    }
+    throw new WritebackError(normalized);
+  }
+  return result;
+}
diff --git a/packages/runtime/src/index.ts b/packages/runtime/src/index.ts
index 1fdf2fa0..a0a11aba 100644
--- a/packages/runtime/src/index.ts
+++ b/packages/runtime/src/index.ts
@@ -110,9 +110,13 @@ export {
   readTextFile,
   resolveMountRoot,
   writeJsonFile,
+  normalizeWritebackStatus,
   type IntegrationClientOptions,
+  type NormalizedWritebackState,
+  type NormalizedWritebackStatus,
   type WritebackReceipt,
   type WritebackResult,
+  WritebackError,
   RelayfileWritebackError,
   type RelayfileWritebackErrorOptions,
   WorkforceIntegrationError,