Fix streamer bugs and document concurrency limitations in world-local

[Copilot]

The local world implementation had several bugs related to stream handling and lacked documentation about its concurrency limitations.

Changes

Streamer fixes:

• Fixed empty chunk inconsistency: chunks with byteLength === 0 are now skipped in event listeners to match disk reading behavior
• Fixed unreachable type check in writeToStream where string-to-Uint8Array conversion made subsequent string check impossible

// Before: chunk reassigned, making type check unreachable
if (typeof chunk === 'string') {
  chunk = new TextEncoder().encode(chunk);
}
// Later: this check never true
const chunkData = typeof chunk === 'string' ? ... : chunk;

// After: separate variable for clarity
let chunkBuffer: Buffer;
if (typeof chunk === 'string') {
  chunkBuffer = Buffer.from(new TextEncoder().encode(chunk));
}

Filesystem robustness:

• Track temp file creation before cleanup attempt in write() function

Documentation:

• Added JSDoc explaining last-writer-wins semantics for concurrent updates in filesystem-based storage
• Documented limitations in write(), runs.update(), and steps.update()

All existing tests pass (124/124).

Original prompt

The local world seems to be quite buggy, especially when dealing with multiple writers and streams. Look through the code of the local world and identify some potential bugs that need to be fixed

---

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[changeset-bot]

🦋 Changeset detected

Latest commit: b4f8bb1

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

This PR includes changesets to release 13 packages

Name	Type
@workflow/core	Patch
@workflow/world-local	Patch
@workflow/builders	Patch
@workflow/cli	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/web-shared	Patch
workflow	Patch
@workflow/world-postgres	Patch
@workflow/sveltekit	Patch
@workflow/world-testing	Patch
@workflow/nuxt	Patch
@workflow/ai	Patch

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