fix(core): reschedule when requestRender races the loop scheduling - #1086

Closes #789.

What changed

If requestRender() fires while a frame is in flight (this.rendering is true), it is demoted to setting immediateRerenderRequested and returns. The loop's end-of-frame schedule decision at renderer.ts:3995 reads that flag and reschedules, but a request that arrives between that read and this.rendering = false in the finally block is dropped: the read already happened, and after the finally the renderer goes idle with no pending timer.

The reporter's RCA in #789 describes the symptom: blank screen with rendering=false scheduled=false running=false, the process otherwise healthy, modals still rendering on top — the next paint never fires.

The fix re-checks immediateRerenderRequested inside the loop's finally, clears it, and re-issues the request via setImmediate.

   } finally {
     this.rendering = false
     if (this._destroyPending) {
       this.finalizeDestroy()
+    } else if (this.immediateRerenderRequested) {
+      this.immediateRerenderRequested = false
+      setImmediate(() => {
+        if (!this._isDestroyed) this.requestRender()
+      })
     }
     this.resolveIdleIfNeeded()
   }

Why setImmediate (not nextTick)

On the one-off (paused / idle) scheduling path, activateFrame keeps updateScheduled = true until its own finally runs, and that finally runs after loop()'s finally. process.nextTick fires before microtasks resume, which means it runs before activateFrame's finally — at which point requestRender() is blocked by the !updateScheduled guard at line 1247 and silently no-ops. setImmediate runs after the microtask queue drains, by which point updateScheduled is back to false and the request schedules normally.

How I verified

cd packages/core && bun test src/tests/renderer.control.test.ts — 29 pass, 0 fail. New test "loop() finally reschedules when requestRender races the schedule decision (#789)" exercises the one-off path:

1. Start + pause renderer
2. Monkey-patch clock.clearTimeout (called in the loop's else branch at line 4004) to fire a sync requestRender() while rendering is still true
3. Assert renderCount >= 2

Confirmed the test fails without the fix (Received: 1) and passes with it by reverting renderer.ts and re-running.

Also ran the broader bun test src/tests/renderer* sweep — 408 pass, 0 fail. bunx oxfmt applied.