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docs/content/docs/cookbook/common-patterns/distributed-abort-controller.mdx

@@ -0,0 +1,318 @@
+---
+title: Distributed Abort Controller
+description: A distributed AbortController that uses durable workflows for cross-process cancellation signaling.
+type: guide
+summary: Build a distributed abort controller that uses workflow streams and hooks to propagate cancellation signals across process boundaries.
+---
+
+Use this pattern when you need an `AbortController`-like interface that works across distributed systems. The controller uses a durable workflow to coordinate cancellation — calling `.abort()` on one machine triggers the `.signal` on any other machine.
+
+## When to use this
+
+- **Cross-process cancellation** — Cancel a long-running operation from a different server, worker, or edge function
+- **Durable cancellation** — The abort signal persists even if the process that created it crashes
+- **UI stop buttons** — Let users cancel operations running on the server from the browser
+- **Timeout coordination** — The built-in TTL auto-expires stale controllers
+
+## Pattern
+
+The `DistributedAbortController` class encapsulates a workflow that:
+1. Accepts a user-provided unique ID (like a chat ID or task ID)
+2. Creates or reconnects to an existing workflow using that ID
+3. Waits for a hook signal OR TTL expiration
+4. Writes a cancellation message to the run's stream when triggered
+
+### Core Implementation
+
+```typescript lineNumbers
+import { defineHook, getWritable, sleep } from "workflow";
+import { start, getRun, getHookByToken } from "workflow/api";
+
+// Default TTL: 24 hours
+const DEFAULT_TTL_MS = 24 * 60 * 60 * 1000;
+// Default grace period: 1 hour (keeps hook alive after abort for late subscribers)
+const DEFAULT_GRACE_MS = 60 * 60 * 1000;
+
+// Hook to trigger the abort signal
+export const abortHook = defineHook<{ reason?: string }>();
+
+// The abort message written to the stream
+export type AbortMessage = {
+  type: "abort";
+  reason?: string;
+  expired?: boolean;
+};
+
+// Helper to create a consistent hook token from the user ID
+function getAbortToken(id: string): string {
+  return `abort:${id}`;
+}
+
+// Step function that writes the abort message to the stream
+async function writeAbortSignal(reason?: string, expired?: boolean) {
+  "use step";
+
+  const writable = getWritable<AbortMessage>();
+  const writer = writable.getWriter();
+  try {
+    await writer.write({ type: "abort", reason, expired });
+  } finally {
+    writer.releaseLock();
+  }
+  await writable.close();
+}
+
+// Workflow that waits for abort or TTL expiration
+export async function abortControllerWorkflow(
+  id: string,
+  ttlMs: number,
+  graceMs: number
+) {
+  "use workflow";
+
+  const startTime = Date.now();
+  const hook = abortHook.create({ token: getAbortToken(id) });
+
+  // Race: manual abort OR TTL expiration // [!code highlight]
+  const result = await Promise.race([
+    hook.then((payload) => ({
+      reason: payload.reason,
+      expired: false,
+    })),
+    sleep(`${ttlMs}ms`).then(() => ({
+      reason: "Controller expired",
+      expired: true,
+    })),
+  ]);
+
+  await writeAbortSignal(result.reason, result.expired);
+
+  // Only sleep through grace period on TTL expiration (keeps hook alive for late subscribers). // [!code highlight]
+  // Manual aborts complete immediately.
+  if (result.expired) {
+    const elapsed = Date.now() - startTime;
+    const remainingTime = graceMs - (elapsed - ttlMs);
+    if (remainingTime > 0) {
+      await sleep(`${remainingTime}ms`); // [!code highlight]
+    }
+  }
+
+  return { aborted: true, reason: result.reason, expired: result.expired };
+}
+
+/**
+ * A distributed abort controller that works across process boundaries.
+ * Uses a semantically meaningful ID (like a chat ID or task ID) to coordinate.
+ */
+export class DistributedAbortController {
+  private id: string;
+  readonly runId: string;
+
+  private constructor(id: string, runId: string) {
+    this.id = id;
+    this.runId = runId;
+  }
+
+  /**
+   * Creates or reconnects to a distributed abort controller.
+   * If a controller with this ID already exists, reconnects to it.
+   * Otherwise, starts a new workflow.
+   *
+   * @param id - A unique, semantically meaningful ID (e.g., "chat:123")
+   * @param options.ttlMs - Time-to-live in ms (default: 24 hours)
+   * @param options.graceMs - Grace period after abort (default: 1 hour)
+   */
+  static async create( // [!code highlight]
+    id: string,
+    options: { ttlMs?: number; graceMs?: number } = {}
+  ): Promise<DistributedAbortController> {
+    const { ttlMs = DEFAULT_TTL_MS, graceMs = DEFAULT_GRACE_MS } = options;
+    const token = getAbortToken(id);
+
+    // Try to find an existing run with this hook token
+    const existingHook = await getHookByToken(token).catch(() => null); // [!code highlight]
+
+    if (existingHook) {
+      // Reconnect to existing controller
+      return new DistributedAbortController(id, existingHook.runId);
+    }
+
+    // Create a new workflow
+    const run = await start(abortControllerWorkflow, [id, ttlMs, graceMs]); // [!code highlight]
+    return new DistributedAbortController(id, run.runId);
+  }
+
+  /**
+   * Triggers the abort signal.
+   * Idempotent: safe to call multiple times or after the workflow has completed.
+   */
+  async abort(reason?: string): Promise<void> { // [!code highlight]
+    try {
+      await abortHook.resume(getAbortToken(this.id), { reason });
+    } catch (error) {
+      const msg = error instanceof Error ? error.message.toLowerCase() : '';
+      if (msg.includes('not found') || msg.includes('expired')) {
+        return;
+      }
+      throw error;
+    }
+  }
+
+  /**
+   * Returns an AbortSignal that fires when abort() is called or TTL expires.
+   * The signal fires with a reason indicating what triggered it.
+   */
+  get signal(): AbortSignal { // [!code highlight]
+    const run = getRun<{ aborted: boolean; reason?: string; expired?: boolean }>(this.runId);
+    const controller = new AbortController();
+    const readable = run.getReadable<AbortMessage>();
+
+    (async () => {
+      const reader = readable.getReader();
+      try {
+        while (true) {
+          const { done, value } = await reader.read();
+          if (done) break;
+          if (value.type === "abort") {
+            const reason = value.expired
+              ? `${value.reason} (expired)`
+              : value.reason;
+            controller.abort(reason);
+            break;
+          }
+        }
+      } catch (error) {
+        if (!controller.signal.aborted) {
+          controller.abort(
+            error instanceof Error ? error.message : "Stream read failed"
+          );
+        }
+      } finally {
+        reader.releaseLock();
+      }
+    })();
+
+    return controller.signal;
+  }
+}
+```
+
+### Usage: Single Process
+
+```typescript lineNumbers
+import { DistributedAbortController } from "./distributed-abort-controller";
+
+// Create a controller with a meaningful ID
+const controller = await DistributedAbortController.create("chat:user-123");
+
+// Get the signal and use it with fetch
+const signal = controller.signal;
+const response = await fetch("https://api.example.com/long-operation", {
+  signal,
+});
+
+// Later: abort the operation
+await controller.abort("User cancelled");
+```
+
+### Usage: Cross-Process Coordination
+
+```typescript lineNumbers
+import { DistributedAbortController } from "./distributed-abort-controller";
+
+// Process A: Create the controller
+const controller = await DistributedAbortController.create("task:build-123");
+// start long operation using controller.signal...
+
+// Process B: Reconnect and abort (no run ID sharing needed!)
+const sameController = await DistributedAbortController.create("task:build-123"); // [!code highlight]
+await sameController.abort("Cancelled by admin");
+
+// Process C: Reconnect and listen
+const anotherRef = await DistributedAbortController.create("task:build-123");
+anotherRef.signal.addEventListener("abort", (e) => {
+  console.log("Task was cancelled:", (e.target as AbortSignal).reason);
+});
+```
+
+### Custom TTL
+
+```typescript lineNumbers
+import { DistributedAbortController } from "./distributed-abort-controller";
+
+// Short-lived controller for a quick operation (5 minutes)
+const shortLived = await DistributedAbortController.create("quick-task", {
+  ttlMs: 5 * 60 * 1000,
+});
+
+// Long-lived controller for batch jobs (7 days)
+const longLived = await DistributedAbortController.create("batch-job", {
+  ttlMs: 7 * 24 * 60 * 60 * 1000,
+});
+
+// When TTL expires, the signal fires with expired reason
+shortLived.signal.addEventListener("abort", (e) => {
+  const reason = (e.target as AbortSignal).reason;
+  if (reason?.includes("expired")) {
+    console.log("Controller expired, cleaning up...");
+  }
+});
+```
+
+### API Route for Remote Abort
+
+```typescript lineNumbers
+import { DistributedAbortController } from "@/lib/distributed-abort-controller";
+
+export async function POST(
+  request: Request,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  const { id } = await params;
+  const { reason } = await request.json();
+
+  const controller = await DistributedAbortController.create(id);
+  await controller.abort(reason || "Cancelled via API");
+
+  return Response.json({ success: true });
+}
+```
+
+### Client Cancel Button
+
+```tsx lineNumbers
+"use client";
+
+export function CancelButton({ taskId }: { taskId: string }) {
+  const handleCancel = async () => {
+    await fetch(`/api/abort/${taskId}`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ reason: "User clicked cancel" }),
+    });
+  };
+
+  return (
+    <button type="button" onClick={handleCancel}>
+      Cancel Operation
+    </button>
+  );
+}
+```
+
+## Tips
+
+- **Use semantic IDs** — Use meaningful IDs like `chat:123` or `task:abc` instead of random UUIDs
+- **Create is idempotent** — Calling `create()` with the same ID reconnects to the existing controller
+- **TTL auto-cleanup** — Workflows self-terminate after TTL expires; no manual cleanup needed
+- **Signal is a getter** — Each access to `.signal` creates a new listener; cache it if needed
+- **One-shot** — Once aborted or expired, the workflow completes; create a new controller for new operations
+
+## Key APIs
+
+- [`defineHook()`](/docs/api-reference/workflow/define-hook) — type-safe hook for the abort trigger
+- [`getWritable()`](/docs/api-reference/workflow/get-writable) — write abort messages to the stream
+- [`sleep()`](/docs/api-reference/workflow/sleep) — TTL timer for auto-expiration
+- [`start()`](/docs/api-reference/workflow-api/start) — start the abort controller workflow
+- [`getHookByToken()`](/docs/api-reference/workflow-api/get-hook-by-token) — find existing run by hook token
+- [`getRun()`](/docs/api-reference/workflow-api/get-run) — reconnect to the workflow's readable stream

docs/content/docs/cookbook/common-patterns/meta.json

@@ -10,6 +10,7 @@
     "idempotency",
     "webhooks",
     "content-router",
-    "child-workflows"
+    "child-workflows",
+    "distributed-abort-controller"
   ]
 }

docs/content/docs/cookbook/index.mdx

@@ -17,6 +17,7 @@ A curated collection of workflow patterns with clean, copy-paste code examples f
 - [**Webhooks**](/cookbook/common-patterns/webhooks) — Receive HTTP callbacks from external services and process them durably
 - [**Conditional Routing**](/cookbook/common-patterns/content-router) — Route payloads to different step handlers based on content
 - [**Child Workflows**](/cookbook/common-patterns/child-workflows) — Spawn and orchestrate child workflows from a parent
+- [**Distributed Abort Controller**](/cookbook/common-patterns/distributed-abort-controller) — Build a cross-process abort controller using workflow streams and hooks
 
 ## Agent Patterns
 

docs/lib/cookbook-tree.ts

@@ -37,6 +37,7 @@ export const slugToCategory: Record<string, string> = {
   webhooks: 'common-patterns',
   'content-router': 'common-patterns',
   'child-workflows': 'common-patterns',
+  'distributed-abort-controller': 'common-patterns',
 
   // Agent Patterns
   'durable-agent': 'agent-patterns',
@@ -124,6 +125,13 @@ export const recipes: Record<string, Recipe> = {
       'Spawn and orchestrate child workflows from a parent, polling for completion and handling partial failures.',
     category: 'common-patterns',
   },
+  'distributed-abort-controller': {
+    slug: 'distributed-abort-controller',
+    title: 'Distributed Abort Controller',
+    description:
+      'Build a cross-process abort controller using workflow streams and hooks to coordinate cancellation by semantic ID.',
+    category: 'common-patterns',
+  },
 
   // Agent Patterns
   'durable-agent': {