fix(HitTest): don't hang waitUsableRectUpdate when graph stabilizes via processQueue drain

[Antamansid]

Problem

In its deferred branch (when the graph is still isUnstable at call time), waitUsableRectUpdate subscribed its stability check to only two signals — $usableRect and $pendingEntitiesUpdate. But the isUnstable getter depends on three conditions: a zero $usableRect, $pendingEntitiesUpdate, and the hitbox processing queue state (processQueue.isScheduled() || queue.size > 0).
The queue is not a signal, so it never triggers the subscription.

This creates a dead spot: the graph can stabilize purely by draining the queue (a re-entrant second processQueue run), while $usableRect and $pendingEntitiesUpdate already hold their final values (updateUsableRect early-returns on an unchanged rect, pending is already false). Neither signal notifies, so the callback is never invoked and waitUsableRectUpdate hangs forever.

Summary by Sourcery

Ensure HitTest usable-rect waiters resolve when stability is reached via processing-queue drainage rather than signal updates.

Bug Fixes:

• Fix waitUsableRectUpdate hanging when the hit-test graph stabilizes only through a re-entrant processQueue drain that does not change $usableRect or $pendingEntitiesUpdate.

Tests:

• Add regression test covering re-entrant two-batch processQueue runs to verify waitUsableRectUpdate resolves when stability is achieved via queue draining.

[sourcery-ai]

Reviewer's Guide

Ensures HitTest.waitUsableRectUpdate no longer hangs when the graph stabilizes via a re-entrant processQueue drain by adding a regression test and wiring the deferred wait logic to also re-check stability on the HitTest "update" event, in addition to the existing signal subscriptions.

File-Level Changes

Change	Details	Files
Add regression coverage for re-entrant processQueue behavior that stabilizes the graph without further signal changes.	Introduce triggerReentrantProcessQueue helper that simulates a two-batch, re-entrant processQueue run where a second hitbox update is scheduled during the first batch and the graph stabilizes purely via queue draining. Add a new test ensuring waitUsableRectUpdate resolves when stability is achieved through the re-entrant queue drain, validating that callbacks no longer hang in this scenario.	src/services/HitTest.test.ts
Fix deferred waitUsableRectUpdate to observe non-signal-driven stabilization by subscribing its stability check to the HitTest "update" event.	Refactor the deferred branch of waitUsableRectUpdate to store the stability check function in a mutable variable so it can be shared between signal subscriptions and event listeners. Extend cleanup logic to unsubscribe the check handler from the "update" event along with the existing signal unsubscriptions. Subscribe the stability check to the HitTest "update" event so that isUnstable is re-evaluated after every processQueue run, covering cases where the queue draining alone stabilizes the graph without changing $usableRect or $pendingEntitiesUpdate.	src/services/HitTest.ts

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[sourcery-ai]

Hey - I've left some high level feedback:

• In waitUsableRectUpdate, you can avoid the check noop initialization and reassignment by defining check before cleanup and closing over it, which would simplify the control flow and make the subscription/unsubscription logic easier to follow.
• The new triggerReentrantProcessQueue test helper relies on casting to unknown as HitBox with partially implemented objects; consider extracting a small factory or shared helper for these stub hitboxes to reduce duplication and make the intent of the fake implementation clearer.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `waitUsableRectUpdate`, you can avoid the `check` noop initialization and reassignment by defining `check` before `cleanup` and closing over it, which would simplify the control flow and make the subscription/unsubscription logic easier to follow.
- The new `triggerReentrantProcessQueue` test helper relies on casting to `unknown as HitBox` with partially implemented objects; consider extracting a small factory or shared helper for these stub hitboxes to reduce duplication and make the intent of the fake implementation clearer.

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