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fix(app): break ResizeObserver feedback loop in composer docks - #50104
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Defer composer-dock ResizeObserver callbacks to rAF and ignore sub-pixel size deltas so the measure->write-max-height cycle can no longer re-trigger observation within the same frame. Removes the self-sustaining idle layout thrash (renderer ~76% sustained CPU, ResizeObserver error storm) without changing rendered output. Refs anomalyco#38296 anomalyco#43355 anomalyco#33712
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Issue for this PR
Closes #38296
Refs #43355, #33712. The streaming-side cost (#49552) is a separate concern and is intentionally not in this PR.
Type of change
What does this PR do?
The Desktop renderer burns ~76% CPU at idle because composer-dock ResizeObserver callbacks measure height and synchronously write the parent
max-height/marginin the same frame (useSpring-driven), re-triggering observation every frame. It's a self-sustaining layout thrash that floods renderer.log with "ResizeObserver loop completed" errors. On a real 2d5h session: renderer 40h CPU / 53h uptime, 93% of the 1416 RO errors landed in minutes with zero streaming activity, and the storm returns 26s after a relaunch.Fix: defer the four composer-dock RO callbacks (region controller, todo dock, question dock, and the session.tsx promptDock amplifier) to rAF and ignore <1px deltas, so a measure->write cycle can't re-trigger observation within the same frame. Rendered output is unchanged (sub-pixel deltas aren't visible; rAF matches render timing) — only the redundant same-frame layout work is removed. No visual or product change, no animations touched.
How did you verify your code works?
dev;tsgo -b(packages/app typecheck) passes.Screenshots / recordings
N/A — perf-only change, no visual difference intended.
Checklist