Fix two races breaking CI on main

[SawyerHood]

CI on main was failing intermittently from two independent races. Both are ~2% flakes, so they broke main sporadically rather than outright — main run 30406401925 (#884) failed Tests (app), and run 30403074723 (#883) failed Tests (packages).

1. useResourcePagination dropped clicks

useResourcePagination mirrored the derived page back into state from a useEffect. That write-back captured the pre-interaction page, so when a viewport measurement changed pageSize, the queued effect flushed after a click and overwrote it:

1. The measurement raises pageSize 10 → 15. That commit renders page=0 at pageSize=15 while the stored pageSize is still 10, and schedules the write-back with page=0 captured.
2. Under load the effect hasn't flushed when the click lands, so setPage(1) writes {page: 1, pageSize: 15}.
3. React then flushes the stale effect, which sees current.page (1) !== page (0) and resets state to {page: 0, pageSize: 15} — discarding the click.

Instrumenting setPage printed exactly this, and only in the failing runs:

[DIAG] setPage(1) closurePageSize=15 statePageSize=10 statePage=0 renderPageSize=15

This is a real product bug, not just a test flake: a user clicking Next in the instant after a list first measures its row height has the click silently ignored. It affects every paginated resource list — plugins, skills, browse, and automations.

State is now an anchor (the page plus the page size it was chosen under), written only by setPage or a new projection, with the rendered page derived from it. The projection reset moved from an effect to a render-time adjustment so it can't land after an interaction. A side benefit falls out: the anchor survives page-size changes, so remeasuring 15 → 10 rows returns you to the page you picked instead of stranding you on page 1.

2. Cross-package fixture race

plugins/workflows/src/cli.test.ts walks the entire checkout, and the packages CI shard runs every other package's tests concurrently in one turbo invocation. It enumerated packages/plugin-registry/.vendor-fixture-*/app.tsx and then read it after the plugin registry's afterAll deleted it → ENOENT.

The walk now skips dot-directories — covering VCS internals, tool caches, and the scratch trees siblings create in their own package roots (.vendor-fixture-*, and agent-runtime's .bb-codex-outside-*) — and tolerates a path deleted mid-walk. .git/.turbo dropped out of the explicit ignore set since the dot rule subsumes them.

Verification

• The stress harness that reproduced the pagination flake at ~2/128 under 8× contention now runs 160/160 clean.
• New apps/app/src/components/ui/resource-pagination.test.tsx pins the anchor semantics; its first test fails on the original hook (expected +0 to be 1) and passes on the fix. It lives in apps/app because shared-ui has no test runner, matching the existing apps/app/src/components/ui/theme.test.ts convention.
• With a .vendor-fixture-PROOF/app.tsx containing the removed command in place, the workflows test passes (fixture ignored); with the same string in docs/cli-guide-and-skill.md it still fails as intended, so coverage is unchanged.
• turbo run typecheck lint on app/shared-ui/workflows/automations: 0 errors.
• turbo run test: app 292 files, workflows 13, automations 3, plugin-registry 1 — all pass.
• Full CI packages shard: 47/48, with the two previously-racing packages passing concurrently.

Two failures left untouched, both pre-existing and local-only (they pass in CI): @bb/desktop#test needs an Electron binary that was never downloaded in my sandbox, and bb-plugin-tasks#test fails on window.localStorage being undefined — confirmed failing identically on a pristine HEAD.

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