[workflows] Dispose RPC results and introspection modifiers

[samstarling]

Local Workflow execution and introspection can leave RPC resources alive, producing undisposed-result warnings and requests cancelled after their execution context has ended. These changes affect local development and test tooling, not deployed production Workflows.

Dispose step callback results after copying their data, release the temporary modifier used during introspected instance creation, and release each introspector's modifier before aborting its instance. Disposal also handles an unused introspector, repeated calls and failed modifier acquisition. Acquisition errors still surface through modify(), and genuine disposer errors still propagate after aborting the instance. Live results retain typed-array offsets and backing buffers. Compaction remains limited to storage.

When a timeout wins the callback race, retain the callback promise and release its eventual result without delaying retries. Late objects are disposed, unused incoming streams are cancelled, and late rejection or cleanup failure does not replace the original timeout. Successful results remain owned by the existing persistence path.

The fixes live in workflows-shared, which is bundled by Miniflare and the Vitest plugin. The five original lifecycle regressions fail on the unpatched baseline and pass with the fix. Additional cases cover failed acquisition, disposer errors, serialisation boundaries and timeout cleanup. The timeout regressions hold the first callback open until its retry starts, checking late objects, late streams, callback rejection and cancellation failure. The three new cleanup regressions fail without the timeout fix. All 203 shared Workflow tests pass, along with type, lint and formatting checks.

Non-stream step results must satisfy the documented structured-cloneable contract. The existing Durable Object storage write already rejected ordinary function-valued properties. Cloning first also rejects functions attached to arrays instead of letting normalisation silently discard them. Tests cover both cases and confirm that prototype methods do not prevent class-instance data from being cloned. Streams continue through their separate persistence path. The timeout tests observe cancellation on the receiving stream: workerd does not reliably notify the producer across RPC. This change does not address the existing lower-level RPC stream-cancellation diagnostics.

Worked example

Imagine a Workflow containing a step such as this:

await step.do("load data", async () => ({ value: 42 }));

Without this change, a test like this could pass while still producing RPC lifecycle errors:

import { introspectWorkflowInstance } from "cloudflare:test";
import { env } from "cloudflare:workers";
import { it, expect } from "vitest";

it("completes the workflow", async () => {
  const id = crypto.randomUUID();

  await using instance = await introspectWorkflowInstance(
    env.MY_WORKFLOW,
    id,
  );

  await env.MY_WORKFLOW.create({ id });

  await expect(instance.waitForStatus("complete")).resolves.toBeUndefined();
});

Despite the test disposing its introspector with await using, the runtime could log this:

An RPC result was not disposed properly. One of the RPC calls you made expects you to call dispose() on the return value, but you didn't do so. You cannot rely on the garbage collector for this because it may take arbitrarily long before actually collecting unreachable objects.
uncaught exception; exception = workerd/io/io-context.c++:1593: failed: jsg.Error: The Workers runtime canceled this request because it detected that your Worker's code had hung and would never generate a response.

---

• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: this fixes resource cleanup behind existing APIs without changing their public usage.

[changeset-bot]

🦋 Changeset detected

Latest commit: 9c13670

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 9 packages

Name	Type
@cloudflare/workflows-shared	Patch
miniflare	Patch
@cloudflare/vitest-plugin	Patch
wrangler	Patch
@cloudflare/deploy-helpers	Patch
@cloudflare/pages-shared	Patch
@cloudflare/remote-bindings	Patch
@cloudflare/runtime-types	Patch
@cloudflare/vite-plugin	Patch

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[workers-devprod]

Codeowners approval required for this PR:

• @cloudflare/workflows
• ✅ @cloudflare/wrangler

Show detailed file reviewers

• packages/workflows-shared/src/binding.ts: [@cloudflare/workflows]
• packages/workflows-shared/src/context.ts: [@cloudflare/workflows]
• packages/workflows-shared/src/introspection.ts: [@cloudflare/workflows]
• packages/workflows-shared/tests/rpc-lifecycle.test.ts: [@cloudflare/workflows]

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commit: 9c13670