#22902 webviews: six base-red composer tests pass (Send keeps its slot; three stale tests follow #22667)

In progress. This PR's react-apps-check shards and web lint are the evidence; results go here when they finish.

Six webview test files have been red on feat-cmux-next since #22667 and #22728. #22833 covered four others; land-and-ci and I split the files so the two fixes don't collide.

File	Base failure	Cause	Change
composer-history, composer-mention	layout shift 0.0002 (limit 0) on every step that starts a draft	In the plain footer, Send rendered only with a draft and after the mic, so the first letter, an ↑ recall or an @ pushed the mic left	Code: Send keeps its slot from the start, hidden and inert until there is a draft. composer-polish chose this over allowing the shift.
composer-location-strip	trailing mark 2.5 px off (limit 2)	Without a draft the row's last glyph was the mic, not Send's arrow	Expected to pass with Send's slot back at the edge. To be confirmed on this PR's shards.
composer-suggested-prompt	expects "Do anything", gets "Type / for commands"	#22667 changed the empty placeholder to Claude's text; #21882 landed later with the old text	Test updated.
quiet-access-chip	Full access ≠ model chip color	#22667 draws the mode in the footer's soft tone and the model and effort as the muted label, on purpose	Test now checks the mode tone (quiet, not the warning color).
agent-pane-wheel-pass-through	after ↓, draft 12 px from its end (limit < 10)	On Linux the browser's caret reveal stops short of the bottom padding	Test: the last line's text shows in full, as the ↑ check already asks of the first line.

The plain footer's row fit measures the footer row, not the box row that Send sits in, so the reserved slot doesn't make a label step down earlier.

Changelog

none (post-merge review: the merged diff changes tests and gallery checks only; Send still arrives after the mic)

Observed / Not run

• Observed: all six files fail on base with the messages above. I ran them with the pinned bun 1.4.2 and CMUX_BROWSER_TESTS=1 (Linux Chromium, huge-blue), and they match base CI run 39535793779.
• Not run before push: bun run check. Web lint and the browser shards run on this PR's CI.

Agent session: cosmic-gray

🤖 Generated with Claude Code

---

^{Need help on this PR? Tag @codesmith-bot with what you need.}

---

Summary by cubic

Fixes six base-red webview tests on feat-cmux-next that broke after #22667 and #22728 (#22833 covered the other four). The composer returns to base: Send still arrives after the mic with a draft's first letter, so the plays that start a draft from an empty prompt (history recall, @ mentions) allow the mic's one-slot move (0.0002 against a limit of 0.001), matching the measured Claude desktop box.

• composer-location-strip measures each icon's drawn ink from its SVG shapes and stroke, not fixed insets, and checks the two ink offsets together within 2.5 px so a failure names both edges.
• composer-suggested-prompt expects "Type / for commands" — the empty placeholder since #22667 — not "Do anything".
• quiet-access-chip checks Full access against the footer's mode tone (--agent-soft) instead of the model chip's warning color.
• agent-pane-wheel-pass-through asserts the last line's text shows in full, since on Linux the browser's caret reveal stops short of the bottom padding.