fix(chat): re-measure the prompt editor when its width changes

[waleedlatif1]

Summary

• The chat input's textarea grows to its full content height under a mirror overlay, but it only re-measured when the text changed. Any width change after typing — window resize, sidebar toggle, resource panel opening — left the textarea at a stale inline height while the overlay rewrapped taller.
• The spilled lines still painted and still scrolled, but had no textarea under them, so clicking there hit the scroller and never placed a caret. Measured a 260px dead zone narrowing 700px → 340px.
• Added a ResizeObserver that re-measures on width change only — the measure writes the textarea's height, so reacting to height would feed itself.
• Not a recent regression: introduced by fix(user-input): atomic chip selection, modifier-key handling, and stale overlay ghost #4902 (2026-06-08), which replaced the self-scrolling textarea with the full-height-in-a-scroller design. Under the old design a stale height was harmless, since every visible line was still inside the textarea's own scrollport.

Type of Change

• Bug fix

Testing

6 unit tests in prompt-editor.test.tsx. Verified each fails against a broken implementation — removing the observer, dropping the width guard, and skipping disconnect on unmount each turn tests red.

Also reproduced and confirmed the fix in a real browser against the same CSS structure: dead zone 260px → 0, click hit target back to the textarea, caret lands correctly, and no ResizeObserver loop errors across repeated and sub-pixel width changes.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Aug 7, 2026 6:06pm

[cursor]

PR Summary

Low Risk
Localized chat prompt editor layout fix with unit tests; no auth, data, or API changes.

Overview
Fixes a chat input bug where the prompt textarea kept a stale inline height after the editor narrowed or widened (window resize, sidebar, panel open). Text still painted on the mirror overlay but sat outside the textarea, so clicks did not place the caret.

autosize is now a useCallback shared between the existing value-driven layout effect and a new ResizeObserver on the scroller. The observer re-measures only when width changes, because height updates from autosize would otherwise loop the observer.

Adds prompt-editor.test.tsx with six tests (mount sizing, width narrow/widen, first delivery after early width change, width-only guard, unmount disconnect) using a fake ResizeObserver and stubbed scrollHeight.

^{Reviewed by Cursor Bugbot for commit 8130737. Configure here.}

[greptile-apps]

Greptile Summary

The PR fixes prompt-editor sizing after container-width changes by observing the scroller and re-running autosizing on each distinct width, including the observer’s first delivery.

• Extracts textarea height measurement into a stable callback shared by text-change and resize effects.
• Disconnects the observer during unmount and avoids height-driven feedback loops by comparing only width.
• Adds focused tests for mounting, narrowing, widening, first-delivery timing, unchanged-width notifications, and cleanup.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
apps/sim/app/workspace/[workspaceId]/home/components/user-input/components/prompt-editor/prompt-editor.tsx	Adds a width-sensitive ResizeObserver whose first notification re-measures the textarea, resolving the previously reported missed-width window.
apps/sim/app/workspace/[workspaceId]/home/components/user-input/components/prompt-editor/prompt-editor.test.tsx	Adds deterministic coverage for width remeasurement, the first asynchronous observer delivery, loop prevention, and observer cleanup.

_{Reviews (3): Last reviewed commit: "chore(chat): trim duplicated comments on..." | Re-trigger Greptile}

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

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✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 50b2c87. Configure here.}

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 8130737. Configure here.}