fix(vscode): preserve streaming scroll intent

[marius-kilocode]

What Problem This Solves

Chat could snap back to the bottom while a response was streaming after an upward wheel or keyboard gesture. The failure was intermittent when the gesture landed on message controls, was only one pixel, or raced a pending bottom scroll and status transition.

Why This Change Was Made

The auto-scroll state now records the latest viewport position, preserves newer upward intent across pending scroll events, does not force-follow when work resumes if the user is paused, and treats upward keyboard input as a pause. Regression coverage exercises the real MessageList story with native wheel and keyboard input.

User Impact

Users can read earlier output while streaming without the transcript pulling them back to the bottom. Explicitly returning to the bottom still resumes auto-follow.

Evidence

• Controlled visible VS Code Agent Manager reversal runs: 5/5 failures before the fix, 0/5 after; snap-back reduced from 282 px to 0 px.
• Prior sidebar and Agent Manager edge cases: 24/24 failures before, 0/24 after.
• 38 scroll-hook tests and 10 browser regression tests pass.
• Extension build, lint, typecheck, Knip, and annotation checks pass.
• Live local SSE streaming flow verified send, streaming, pause, resume, and stop behavior.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (6 files)

• .changeset/fix-streaming-scroll-intent.md
• packages/kilo-ui/src/hooks/create-auto-scroll.test.tsx
• packages/kilo-ui/src/hooks/create-auto-scroll.tsx
• packages/kilo-ui/src/hooks/scroll-user-activity.ts
• packages/kilo-vscode/tests/chat-auto-scroll.spec.ts
• packages/kilo-vscode/webview-ui/src/stories/chat.stories.tsx

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[WebReflection]

Interesting, I had similar issues and I've fixed it in a simpler way here and here.

I am writing this for historical sake, no action needed, it's just a possible future reference in case we'd like to refactor current streaming logic and simplify a bit the scrolling common issue all streaming content has.