Install CJK fonts in the browser gate and regenerate the Linux visual baselines

package.json

@@ -30,7 +30,7 @@
     "check:webui-dependency": "node scripts/check-webui-dependency.mjs",
     "test:webui": "node scripts/run-vitest-suite.mjs webui",
     "test:webui-package": "node scripts/verify-webui-package.mjs",
-    "test:webui-browser": "playwright install chromium && playwright test packages/webui/test/browser",
+    "test:webui-browser": "playwright install --with-deps chromium && playwright test packages/webui/test/browser",
     "typecheck:webui": "pnpm --filter @mavis/webui typecheck:server && pnpm --filter @mavis/webui typecheck:client && pnpm --filter @mavis/webui typecheck:test",
     "check:source": "node scripts/source-inventory.mjs",
     "check:plugin": "node tools/plugins/validate-plugin.mjs",

packages/webui/docs/verification/browser-suite.md

@@ -4,7 +4,9 @@
 `styles.css` and files under `assets/` — in a real browser. The deterministic harness server serves
 those built assets from the client output directory and refuses paths outside that directory. Run
 `pnpm build:webui` first; the script installs the
-lockfile-pinned Chromium revision when it is missing. The deterministic cases are evidence level 4 in
+lockfile-pinned Chromium revision when it is missing, and on Linux also installs Chromium's system
+dependencies, which include the CJK fonts the Chinese UI renders with. The deterministic cases are
+evidence level 4 in
 [`gates.md`](gates.md): the built client and its transport wiring are real, the server behind them is
 not in the deterministic fixture cases. `native-runtime.spec.mjs` additionally boots the real
 assembly, loopback service and native PTY bridge in a separate process with an isolated,
@@ -99,10 +101,22 @@ pnpm build:webui
 pnpm test:webui-browser
 ```
 
+The screenshots are only comparable within one font environment. The gate installs Chromium's
+Linux system dependencies, which include the CJK fonts the Chinese surfaces need; on a runner
+without them the browser has no glyph to draw for Chinese text and renders tofu boxes instead.
+The committed baselines therefore record real Chinese glyphs, and a reviewer reading a diff can
+read the Chinese in it. The same applies in reverse: regenerating the baselines anywhere that
+does not install those fonts produces boxes, and the comparison against the committed baselines
+fails. Treat a font change on the runner as a baseline change, not as a rendering difference to
+be accepted.
+
 To deliberately regenerate only these baselines, use
 `pnpm exec playwright test packages/webui/test/browser/visual-baselines.spec.mjs --update-snapshots`
 on Linux CI Chromium, inspect every resulting image, then run the same command without
-`--update-snapshots` to compare. A passing fixture screenshot proves the built client's rendered
+`--update-snapshots` to compare. Regenerate on a Linux environment that has the gate's fonts
+installed — `pnpm exec playwright install --with-deps chromium` before the run — so the new
+baselines carry the same glyphs the committed ones do. A passing fixture screenshot proves the
+built client's rendered
 state under the in-page deterministic transport; it does not prove the production service or runtime
 path. Those boundaries require the integration suites described above.
 

packages/webui/test/browser/README.md

@@ -5,7 +5,7 @@ in-page transport). Run the directory, not a hand-kept list: Playwright collects
 
 ```sh
 pnpm build:webui          # the suite drives the built client
-pnpm test:webui-browser   # installs the pinned Chromium revision when missing
+pnpm test:webui-browser   # installs the pinned Chromium revision and, on Linux, its system dependencies
 ```
 
 How the fixture works, what the suite proves and what it does not, and which environment variables