refactor(ui): drop the dead [data-trow] chat rules

[Astro-Han]

Summary

chat-message.css still carried four rules keyed on [data-trow]: the hover arm inside @media (hover: hover), and the .astryx-collapsible-trigger type/box rule plus its two chevron-sizing rules. Nothing renders that attribute any more.

The attribute went away in 6745aa1 ("render every tool row through Astryx"), which retired the bespoke trow renderer — data-trow="group" / data-trow="row" were emitted by packages/ui/src/tool-activity.tsx and are deleted in that diff — and moved permission / sandbox / interrupted rows onto Astryx ChatToolCalls. Confirmations: no data-trow anywhere in packages/*/src or apps/desktop/src outside this stylesheet, and grep -o data-trow apps/desktop/dist-renderer/assets/*.js is empty, so the shipped bundle has no element these selectors could match.

The block's long comment split three ways rather than going wholesale:

• Dead with the rules. "Product trow (permission / sandbox / interrupted): Collapsible defaults large" describes a renderer that no longer exists.
• Live, and about the rules above. Product CSS in the components layer beats Astryx's StyleX atoms on layer order alone, which is why this file declares no !important. That is a fact about the surviving reasoning/tool-call icon boxes, so it moves onto them — minus its count of "all eight" flags, since some of those lived on the rules deleted here and the number no longer resolves to anything a reader can check. The mechanism it was evidence for still holds.
• Dropped. The --maka-line-body note. That token's only use in this file is the supporting-leading rebind one rule earlier, which its own comment already explains; the rules the note sat above declare nothing but width and height, so it had no force where it stood.

--maka-line-body, --radius-element and --maka-text-label all keep live consumers elsewhere in the file, so nothing became a dead token.

One follow-on: check-dead-css.mjs keeps astryx-collapsible-trigger in DYNAMIC_STYLE_HOOKS with a comment pointing at chat-message.css. After this change its only consumer is styles/settings/permission.css, so the comment is retargeted; the allowlist entry itself is still needed.

Why check:stale did not flag this — and what actually should have

check:stale is scripts/check-stale-dist.mjs. It compares src mtimes against dist mtimes per workspace to force a rebuild before tests. It never reads CSS and has no opinion about selectors, so it was never going to catch this — no gap there.

The tool that is meant to catch dead CSS is scripts/check-dead-css.mjs (wired into check:release, not check:stale). It also misses these rules, and that is the real find. Its class scan matches /\.(-?[_a-zA-Z][_a-zA-Z0-9-]*)/ — class selectors only — and its token scan looks at --custom-properties. An attribute selector such as [data-trow] is in neither vocabulary, so a rule can be keyed entirely on a data-* hook that no component renders and the script still reports "no dead classes or tokens found ✓", exactly as it does before and after this PR.

The two classes in these selectors did not help either: maka-turn and astryx-collapsible-trigger are both live elsewhere (astryx-collapsible-trigger is in the DYNAMIC_STYLE_HOOKS allowlist precisely because it is rendered at runtime), so even a per-rule liveness check that reasoned over class names alone would have called this rule live. Detecting it requires scanning the data-* attribute hooks a stylesheet keys on and checking each against source — a real extension to the script rather than a config tweak, and one that needs its own baseline because the renderer keys plenty of live rules on data-* ([data-sender], [data-maka-contract] in this file alone).

Not doing that extension here: it would land a new detector plus its own baseline alongside an unrelated cleanup. Flagging it so the gap is on the record.

Verification

Rebased onto main after #2228 landed; the two changes touch adjacent but disjoint rules in this stylesheet and merged without conflict.

• npm run format / npm run format:check / npm run lint — clean (Biome, no fixes applied).
• node scripts/check-dead-css.mjs — no dead classes or tokens found ✓ (unchanged, and per above, unchanged for the wrong reason).
• node --test scripts/check-dead-css.test.mjs — 13/13 pass.
• CSS contract tests under apps/desktop/src/main/__tests__/: node --test "dist/main/**/*contract*.test.js" "dist/main/**/css-test-helpers.test.js" — 145/145 pass, 35 suites. This covers every test that parses this stylesheet through css-test-helpers / contract-css-helpers, including chat-reasoning-wrap-contract and fix(ui): draw the reasoning chevron from the Astryx icon registry #2228's chat-disclosure-chevron-contract (the latter asserts the reasoning and tool-call rows declare a 10x10 chevron svg and wrapper, which the deleted trow rules never contributed to).
• tsc -p tsconfig.main.json reports pre-existing errors in runtime-host / oauth / voice tests. They reproduce identically on a clean main checkout and are unrelated to this change.
• No live-app screenshot: the deleted rules cannot match any rendered element, so there is no before/after to show. The bundle grep above is the evidence that rendering is untouched.