Agent chat: a long draft scrolls in the composer alone

Merged
TE
16d ago
+78-9

Summary

A long draft in the agent chat composer now scrolls only itself. Before, reaching its top or bottom kept going and scrolled the transcript.

  • wheelPassThrough.ts: a scroller under the pointer (a long prompt, the queue, a menu list) keeps the wheel at its ends too. The wheel still goes to the transcript over parts that don't scroll (Jump to latest, the card's chrome, a short draft).
  • markdownField.css, composerStates.css: the markdown and shell fields get overscroll-behavior: contain, so there's no chaining and no bounce.
  • MarkdownField.tsx: scrollMargin: 16 so typing scrolls the caret's whole line into view.

The first version also moved the field 6px in from the card's corner. That moved the field edges the strip and queue alignment tests measure, and #22667 (composer-polish) owns the card's padding and corner, so it was dropped. Whichever of the two lands second checks that the scroller stays inside the corner.

Takes back #22341: only its "wheel passes on once the long prompt reaches its end" part. Leo, 2026-10-20: "when I reach the top or the bottom, I don't want that to shift". Every other pass-through from #22341 stays.

Changelog

Fixed: Scrolling a long draft in the agent chat composer no longer scrolls the transcript when it reaches the top or bottom.

Testing

Command: cd webviews && CMUX_BROWSER_TESTS=1 bun test test/agent-pane-wheel-pass-through.test.ts (real Chromium and WebKit wheel events).

  • Base (test commit 2ea6e77f6b79 on the old sources): red. Wheeling up at the top of a long draft scrolled the transcript by -1933px.
  • Head: CI's browser lane runs it (see Observed / Not run).

Observed / Not run

  • Observed: the red above, run locally earlier in this session. On the first head the case passed locally on macOS, but CI on Linux failed it at the ↑ step: the draft's scrollTop was 10, not 0. The 6px inset also turned 20 strip and queue alignment cases red. The second commit drops the inset and checks instead that the first line is fully in view.
  • Not run: the second commit locally. Tests and git are frozen on this Mac (load), so it was committed through the GitHub API and CI is the check. No look in a native app build.

Agent session: cosmic-gray

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