perf(runtime): wake the FIFO batch loop when a mutation arrives

[kyscott18]

Summary

In FIFO mode, the runtime polled the received-mutation queue every 4 ms, so each mutation waited for the next tick. That wait was most of the latency for a single client. The loop also woke 250 times per second when idle.

• FIFO now blocks on Queue.takeAll and accepts all mutations that queued while the previous batch ran.
• Batch mode keeps its fixed window, because it needs one to reorder by batchOrder.
• Both modes take mutations outside the speculative-state lock, so a wait never blocks submit.

Most of the diff is reindentation: acceptBatch now receives the drained mutations. git diff -w shows +29/−14.

Results

Counter benchmark, 1 client: 4.04 ms → 1.56 ms average; 247 → 641 mutations/s.

Test plan

• bun run lint, bun run typecheck, bun run test

🤖 Generated with Claude Code

Confidence Score: 5/5

The PR appears safe to merge; the remaining FIFO test gap is non-blocking.

Findings

1.  FIFO changes escape tests ▶

Fix with agent prompt

### Issue 1
packages/typewriter/src/runtime.ts:1109-1112
Both helpers in `runtime.test.ts` select batch mode, so the existing suite never exercises the new `Queue.takeAll` branch. The suite can pass even if FIFO acceptance or submission breaks. Add a FIFO test that waits while idle, accepts consecutive mutations in arrival order, and confirms that `submit` can still run while the queue is empty.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Summary

FIFO now waits for mutations with Queue.takeAll instead of polling every 4 ms.

• FIFO accepts queued mutations when they arrive instead of waiting for a timer tick.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  Mode{Sequencing mode}
  Mode -->|FIFO| Wait["Queue.takeAll waits for mutations"]
  Mode -->|Batch| Window["Wait for fixed batch window"]
  Window --> Drain["Queue.clear drains mutations"]
  Wait --> Accept["acceptBatch takes speculative-state lock"]
  Drain --> Accept
  Accept --> Persist["Accept and persist mutations"]
  Persist --> Ready["Queue batch for submit"]
  Ready --> Mode

Loading

_{Reviews (2) · Last reviewed commit: "refactor(runtime): inline the accept bat..." · Reviewed by Greptile}

[greptile-apps]

FIFO changes escape tests

Both helpers in runtime.test.ts select batch mode, so the existing suite never exercises the new Queue.takeAll branch. The suite can pass even if FIFO acceptance or submission breaks. Add a FIFO test that waits while idle, accepts consecutive mutations in arrival order, and confirms that submit can still run while the queue is empty.

Prompt To Fix With AI

This is a comment left during a code review.
Path: packages/typewriter/src/runtime.ts
Line: 1113-1116

Comment:
**FIFO changes escape tests**

Both helpers in `runtime.test.ts` select batch mode, so the existing suite never exercises the new `Queue.takeAll` branch. The suite can pass even if FIFO acceptance or submission breaks. Add a FIFO test that waits while idle, accepts consecutive mutations in arrival order, and confirms that `submit` can still run while the queue is empty.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!