fix(max): constrain chat textarea height

[lordspline]

Problem

Long messages in the PostHog AI agent chat cause the input box to grow beyond 100% of the viewport height, making the send button inaccessible.

Changes

• Added QuestionInput__textarea class to the AI chat input component
• Constrained textarea max-height to min(40vh, 20rem) with vertical overflow scrolling
• Added test to verify the constrained scrolling styles are applied

How did you test this code?

Ran automated tests in QuestionInput.test.tsx—all tests pass, including new test that verifies the textarea renders with constrained scrolling styles.

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[capy-ai]

🎨 Visual QA — fix(max): constrain chat textarea height

Surface: Max AI chat (/ai) — textarea on QuestionInput
Tested: desktop 1280×900 and narrow 375×812, empty state and long-text state (12 lines)

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Empty state — no visible change (✅ expected)

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Long text — desktop 1280×900

Before (master): textarea grows to ~10 rows with no height cap, send button stays on-screen due to maxRows={10} already limiting it.
After (PR): max-height: min(40vh, 20rem) kicks in — textarea is capped at 20rem (320px), vertical scrollbar appears, send button always visible.

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Long text — narrow 375×812

The constraint matters most here: min(40vh=150px, 20rem=320px) → 150px cap, so at mobile-viewport heights the textarea scrolls well within the visible area.

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Summary

	Empty	Long text (desktop)	Long text (narrow)
Send button accessible	✅ both	✅ both	✅ both
Textarea height capped	—	✅ after only	✅ after only
Scrollbar appears	—	✅ after only	✅ after only
Layout breaks	—	❌ none	❌ none

Result: ✅ Looks correct. The constraint applies cleanly, the send button remains reachable, and empty state is unaffected. No layout regressions observed at either viewport.

_{Screenshots captured against live local dev stack on master + PR CSS applied via Vite HMR.}