A preview's toolbar page says what its pull changed and whether its check is green, each link a 44 px tap on touch screens #4221

A preview's toolbar page now has a change line under the head line, and I've pushed the branch again. The failure that parked #4219 was in a test outside this change, and I could not reproduce it.

• The change line: it shows "N files, +A −R" linking to the pull's Files page, and the latest check as a badge linking to its log. With no check it shows a plain "No check" badge.
• Diff stat and links: the diff stat is read once per pull and head oid. The links are at least 36 px tall, and 44 px under @media (pointer: coarse). .change-line is named in docs/DESIGN.md §5d with that note.
• Production and access: production's toolbar page is unchanged, and a pull the viewer may not see still returns 404.
• The parked failure: the check that failed was "Fork lands on the job, then on the fork's mirror saying whose it is" in test/web-workflows.test.ts. My change only touches toolbarPage, the diff-totals helper, one stylesheet block and the docs, so I don't think it can affect fork or mirror pages. I merged current main and ran that file twice here, and all 23 tests pass both times. I did not change that test.
• Verification: bun x tsc --noEmit is clean. The toolbar tests and test/design-lint.test.ts pass (93 tests), including test/toolbar-change-line.test.ts, which covers a green check, a red check, none, and the under-50 ms repeat request.
• Left out and risk: there is no test for a sealed pull; the 404 comes from the existing mayView check. The cache is keyed on head oid only, so totals can lag if the base branch moves while the head stays put. If the forge's check fails on that fork test again, treat it as a flake or a separate bug and look at its log.

To try it, open /<owner>/<app>/toolbar?env=pull-N on a preview.

Closes #4205

A preview's toolbar page now has a change line under the head line, and I've pushed the branch again. The failure that parked #4219 was in a test outside this change, and I could not reproduce it.

• The change line: it shows "N files, +A −R" linking to the pull's Files page, and the latest check as a badge linking to its log. With no check it shows a plain "No check" badge.
• Diff stat and links: the diff stat is read once per pull and head oid. The links are at least 36 px tall, and 44 px under @media (pointer: coarse). .change-line is named in docs/DESIGN.md §5d with that note.
• Production and access: production's toolbar page is unchanged, and a pull the viewer may not see still returns 404.
• The parked failure: the check that failed was "Fork lands on the job, then on the fork's mirror saying whose it is" in test/web-workflows.test.ts. My change only touches toolbarPage, the diff-totals helper, one stylesheet block and the docs, so I don't think it can affect fork or mirror pages. I merged current main and ran that file twice here, and all 23 tests pass both times. I did not change that test.
• Verification: bun x tsc --noEmit is clean. The toolbar tests and test/design-lint.test.ts pass (93 tests), including test/toolbar-change-line.test.ts, which covers a green check, a red check, none, and the under-50 ms repeat request.
• Left out and risk: there is no test for a sealed pull; the 404 comes from the existing mayView check. The cache is keyed on head oid only, so totals can lag if the base branch moves while the head stays put. If the forge's check fails on that fork test again, treat it as a flake or a separate bug and look at its log.

To try it, open /<owner>/<app>/toolbar?env=pull-N on a preview.

The check failure is fixed and pushed. The tight-bound guard in test/flake.test.ts was rejecting the new test/toolbar-change-line.test.ts, which asserted a repeat read of the pull page took under 50 ms. The guard forbids wall-clock bounds below 200 ms. I loosened that one bound to toBeLessThan(200).

Locally, test/toolbar-change-line.test.ts and test/flake.test.ts pass, 31 tests in all. I didn't run the whole suite, since the forge runs that on the push.

The test still checks that the second read comes from the cached stat. It just allows more time than before.

I merged main into the branch, resolved the two conflicts, and pushed. The type check and design lint are clean. 82 tests pass across the toolbar tests, flake.test.ts, design-lint.test.ts and server-timing-sweep.test.ts. I did not run the whole suite.

• src/web/studio/toolbar.ts: main added a "Sign in to comment" button, with a next link back to the same page, to the signed-out toolbar page. I kept that button and kept the change line (diff totals and check badge) in front of it, so signed-out visitors see both.
• docs/DESIGN.md: I took main's component lists and added .change-line back to the apps, runs and crew entry. main had dropped .no-hits from the search-results entry, so I left it out.

I've pushed fixes for all four points. I kept .change-line as a new class and didn't redo the extra getPull. Tests, the type check and design lint pass locally; I didn't run the full suite.

Design rules

• docs/DESIGN.md is back to main's version.
• .change-line is now named in docs/design/areas/toolbar.md.
• I kept the class rather than building it from a stack plus the badge. §5 has no inline row of links with a 36 px target (44 px on touch), and that sizing is the point of the change. The area file says so.

Your numbered points

1. Failed stat: the totals now use diffBetween, which reports when git failed. On failure the diff link is left out and nothing is cached, so it reads as unavailable rather than "0 files". The check badge still shows.
2. Stale cache: the key is now the pull, its head oid and the live base oid, read from the base branch ref.
3. Cache test: it now counts git reads through an exported statReads counter. A second read adds none, and moving the base adds exactly one. A new test shows the diff link is absent when git can't give the totals.
4. Tidy:

- The as never cast is gone; check.run.state is already the right type. - Imports are in order. - The test header cites #4221. - I did not remove getPull. The page loads an Issue, which has no headOid. I tried loading the pull directly, but toolbar-actions.test.ts creates a pull-kind issue with no pull row, and the page then returned 404, so I reverted. I added a comment on the getPull call and showed no change line when there is no pull row.

I've pushed the fixes for all three points to the same branch. The toolbar tests, flake.test.ts, design-lint.test.ts and scripts/design-lint.ts pass. I didn't run the whole suite.

• Sizing: each .change-line link is now 40px tall, set by padding with line-height: 16px. Under pointer: coarse the padding grows to 44px. The min-height: 36px rule is gone. If the badge is taller than 16px, the link comes out taller than 40px, never shorter.
• Shared colours: .change-line .add and .change-line .del are added to the existing .diff-summary .add and .diff-summary .del selectors, so the declarations are no longer copied.
• README: I added one sentence to the toolbar-page paragraph. It says a preview shows what the pull changed and where its latest check stands, each linked, and that the totals are left out when git can't give them.
• Why a new class: docs/design/areas/toolbar.md now says why. .diff-summary is a padded block, not a row of separately tappable links, and the badge is not a link target itself. Neither carries the 40/44px sizing.