build(web): rebuild plugin bundles before the browser lane

test:web ran build:web alone, which does not rebuild UI plugin client
bundles. Plugin CSS reaches the browser through packages/client/*/lib/
client.js, not apps/web/dist, so a changed *.module.css served its
previous bundle: the run exercised stale CSS and a removed declaration
still passed. That is how I first mistook a valid gutter test for a
vacuous one.

Root build already covers packages/*/*, so running it first is enough;
check-all already ordered build before build:web, so CI was never
exposed. Only the local script was, which is where a stale-bundle pass is
most likely to be believed.

Verified against the situation it fixes: mutate the source, rebuild the
bundle, restore the source, and the artifact is left without the
declaration while the source has it. Under the old script the run tested
that artifact; under the new one the artifact is rebuilt first (grep goes
0 to 1) and the scrollbar spec passes. The nine failing web files are the
pre-existing aria-golden set from f2c004524, unchanged by this.

docs/testing.md

@@ -10,7 +10,7 @@ How this repo tests, tier by tier, and the rules that keep a green suite meaning
 - **Coverage gate** (`pnpm run test:coverage`): the gating run, per-file 100% on `packages/*/*/src`. An uncovered line is often dead code the gate is correctly flagging for deletion, not a missing test to bolt on. Line coverage is necessary, never sufficient — it proves lines ran, not that the feature works as shipped.
 - **Real-API e2e** (`pnpm run test:e2e`): with-key tests against live provider APIs — the DeepSeek model plus provider-specific smokes that gate on their own keys (`EXA_API_KEY`, `PERPLEXITY_API_KEY`, …); each suite self-skips without its key so keyless CI stays green ([real-API e2e Agent Note](../.agents/notes/implemented/testing/2026-06-19-real-api-e2e-ci.md)).
 - **Snapshot** (`pnpm run test:snapshot`): keyless expected outputs cover external behavior — transport contracts and presentation, while persisted logs pin assembled backend behavior. ACP boots the real automation-server example, replays a recorded session, and diffs normalized JSON-RPC plus the re-persisted log ([ACP snapshot Agent Note](../.agents/notes/implemented/testing/2026-06-19-acp-snapshot-tests.md)); headless pins `stream-json` through its real one-shot process. TUI journeys replay primary/child JSONL through the real loop and tools, then project ANSI into semantic terminal-state outputs; package snapshots retain transient states and a real PTY covers the process boundary ([TUI snapshot Agent Note](../.agents/notes/implemented/testing/2026-07-18-tui-terminal-state-snapshots.md)). Use `pnpm run test:snapshot:record` when a model transcript changes and `pnpm run test:snapshot:refresh` when replay input remains valid; review every JSONL and expected-output diff. One ACP scenario (`text-turn`) pins full system-prompt/tool-schema content; other fixtures tokenize it so an edit churns one line ([pinned-header Agent Note](../.agents/notes/archived/testing/2026-07-06-pin-request-header-content-in-one-scenario.md)).
-- **Web browser snapshot** (gate-exempt `pnpm run test:web`): real chromium over the in-process web composition replays recorded fixtures against conversation aria goldens (`apps/web/tests/snapshots/`); record/refresh semantics and the deferred CI browser decision: [web e2e lane Agent Note](../.agents/notes/implemented/testing/2026-07-24-web-gui-browser-e2e-lane.md).
+- **Web browser snapshot** (gate-exempt `pnpm run test:web`): real chromium over the in-process web composition replays recorded fixtures against conversation aria goldens (`apps/web/tests/snapshots/`); record/refresh semantics and the deferred CI browser decision: [web e2e lane Agent Note](../.agents/notes/implemented/testing/2026-07-24-web-gui-browser-e2e-lane.md). [Runs `build` first](../.agents/notes/implemented/bug-fix/2026-07-28-themed-scrollbars-and-reserved-gutter.md): plugin CSS ships per plugin.
 
 Committed session-format JSONL uses the canonical packed-row layout, and the keyless snapshot gate discovers every such fixture by its `session` header. In-flight branches carrying older fixture edits merge current `master` and run the [temporary migrator](../scripts/migrate-packed-session-fixtures.ts) through `pnpm run migrate:packed-session-fixtures`; the [removal proposal](../.agents/notes/proposed/process/2026-07-26-remove-packed-session-fixture-migrator.md) retires that command and these links after all affected branches converge.