fix(chat): autosize long prompts in the composer

[BillLeoutsakosvl346]

Summary

The initial (hero) composer was pinned to a fixed h-[56px], so a long prompt scrolled inside a two-line box instead of growing. Both views now share one sizing policy — cap at 200px, autosize between — with a 56px resting floor for the hero composer.

- className={isInitialView ? 'h-[56px]' : 'max-h-[200px]'}
+ className={cn('max-h-[200px]', isInitialView && 'min-h-[56px]')}

An earlier revision of this branch also restyled the composer's scrollbar (visible thumb, stable gutter, hover reveal). That has been reverted — it did not do what it claimed, and it cost real layout:

• Chrome ignores ::-webkit-scrollbar customization whenever scrollbar-width is set, and globals.css already applies * { scrollbar-width: thin }. The 4px width, pill radius and 8px track inset were inert. Measured: scrollbar-width:thin + ::-webkit-scrollbar{width:4px} → 11px; with scrollbar-width:auto → 4px.
• What did survive was scrollbar-gutter: stable, which permanently reserved the 11px thin scrollbar. Prompt text sat 11px off-centre — 14px/25px left/right, against 14px/14px before — for every prompt, including a one-word one.
• hover:[&::-webkit-scrollbar-thumb]:… compiles to …::-webkit-scrollbar-thumb:hover, so it targeted the thumb rather than the container, and emitted after the sibling rule at equal specificity — silently overriding the hover colour it sat next to.

The margin/padding pair and the 8px bottom margin went with it; they existed only to position that scrollbar.

Tests

The class-literal assertions are replaced with coverage that can actually fail. The previous scrollHeight stub returned the content height unconditionally, so deleting textarea.style.height = 'auto' — the entire reason autosize can shrink — still passed every test.

The stub now models the browser rule that scroll height is the greater of the text height and the box the element is pinned to. Deleting that collapse now turns both the new shrink test and the existing widen-back test red.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Other

Testing

• bunx vitest run app/workspace/[workspaceId]/home/components/user-input/ — 6 files, 41 tests passed
• Mutation-checked the new coverage: removing the height = 'auto' collapse turns 2 tests red; restoring it turns them green
• Geometry measured in Chromium and WebKit via Playwright against the compiled Tailwind output (source of the 11px / 14px-vs-25px numbers above)
• bun run type-check, bunx biome check, bun run check:api-validation — all pass

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Aug 10, 2026 6:53pm

[cursor]

PR Summary

Low Risk
UI-only composer sizing and test improvements in the chat input; no auth, data, or API changes.

Overview
The hero chat composer no longer uses a fixed 56px height that trapped long prompts in a tiny scroll box. PromptEditor now always caps at 200px and autosizes with content, while the initial view keeps a 56px minimum via min-h-[56px] instead of h-[56px].

Autosize tests were tightened so they can catch regressions: the scrollHeight stub now returns the max of content height and the pinned inline height (matching browsers), and a new case asserts the textarea shrinks when the prompt shortens—covering the height = 'auto' collapse step that growth-only measuring would miss.

^{Reviewed by Cursor Bugbot for commit 956634d. Configure here.}

[greptile-apps]

Greptile Summary

The PR lets the initial chat composer grow with long prompts while retaining a 56px resting floor and a 200px cap.

• Replaces the initial composer’s fixed height with shared minimum/maximum sizing constraints.
• Strengthens autosize tests so shrinking requires clearing the textarea’s inline height before measurement.

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/user-input.tsx	Replaces the initial composer’s fixed height with a conditional 56px minimum and shared 200px maximum.
apps/sim/app/workspace/[workspaceId]/home/components/user-input/components/prompt-editor/prompt-editor.test.tsx	Improves the scroll-height model and adds coverage for shrinking after prompt content becomes shorter.

_{Reviews (3): Last reviewed commit: "fix(chat): drop the composer scrollbar r..." | Re-trigger Greptile}

[BillLeoutsakosvl346]

@greptile

[BillLeoutsakosvl346]

Follow-up in 3605bd7 moves the prompt scroller 6px into the composer right padding while preserving text width, and adds an 8px gap above the toolbar so the scrollbar ends clear of the send button. The focused 10-test suite, Biome, and type-check pass.

[BillLeoutsakosvl346]

demo:

Screen.Recording.2026-08-10.at.11.07.33.AM.mov

[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 956634d. Configure here.}