Optimize chat composer render hot path

[cursor]

What Changed

• Removed the effect-driven composer menu highlight sync and derive the active menu item during render instead.
• Indexed provider instance entries once so composer model/provider resolution avoids repeated linear lookups.
• Stabilized composer editor event handlers so React Scan no longer reports onCommandKeyDown / onPaste prop churn on ComposerPromptEditor.

Why

react-doctor flagged ChatComposer for an O(n*m) provider lookup and a cascading useEffect state sync in the composer menu. React Scan on the /model composer interaction also showed ComposerPromptEditor re-rendering with callback prop changes. This keeps the same behavior while reducing follow-up state work and callback churn in the hot composer path.

Measurements:

• react-doctor web diagnostics: 763 -> 761 total; ChatComposer perf/state findings: 6 -> 4. The js-index-maps provider lookup warning and menu-highlight no-cascading-set-state warning are gone.
• React Scan /model interaction: ComposerPromptEditor change samples changed from props:["onCommandKeyDown","onPaste"] to props:[]; measured editor duration improved from 16.8ms before to 7.1ms after in the captured run.

UI Changes

No visual UI changes expected.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

  

Note

Optimize ChatComposer render hot path with memoized lookups and stable callbacks

• Replaces linear array scans for provider instance lookups with a memoized Map keyed by instanceId, used for lockedContinuationGroupKey, selectedInstanceId, and selectedProviderEntry.
• Introduces useStableCallback to give onComposerCommandKey and onComposerPaste stable function identities across renders without stale closure issues.
• Removes the effect that synchronized composerHighlightedItemId and composerHighlightedSearchKey on menu open; the active item is now derived on-demand via resolveComposerMenuActiveItemId.
• Arrow key nudge now advances from the resolver-derived active item and persists composerHighlightedSearchKey on each nudge.
• Behavioral Change: highlighted item state is no longer eagerly synced via an effect; menus derive active selection lazily instead.

^{Macroscope summarized da1c215.}

---

Note

Medium Risk
Touches core chat composer input/keyboard navigation and provider/model resolution; behavior should be equivalent but subtle menu-highlight or selection regressions are possible. Changes are localized to ChatComposer.tsx and primarily performance-oriented.

Overview
Optimizes ChatComposer render/interaction performance by replacing repeated provider-instance array scans with a memoized Map keyed by instanceId, used for locked continuation group resolution and selected instance/provider entry lookups.

Removes the effect that synchronized menu highlight state and instead derives the active command-menu item during render via resolveComposerMenuActiveItemId; arrow-key nudging now advances from this derived active item and keeps the highlight search key in sync.

Introduces useStableCallback and applies it to onComposerCommandKey and onComposerPaste (and wraps image-attach logic in useCallback) to reduce callback identity churn passed into ComposerPromptEditor.

^{Reviewed by Cursor Bugbot for commit da1c215. Bugbot is set up for automated code reviews on this repo. Configure here.}

[macroscopeapp]

Approvability

Verdict: Needs human review

Performance optimization that removes a useEffect responsible for synchronizing composer menu highlight state. While the intent is optimization, the structural changes to state management timing warrant verification that highlight behavior remains correct.

^{You can customize Macroscope's approvability policy. Learn more.}