Unit tests for the page's own functions (#234)

tests/page-unit.js loads the built index.html script into the stub DOM page-smoke.js uses and
calls its helpers directly with node:test: escaping, times and sizes, file kinds, an untitled
item's name, the directory's sorts, filter words, DeadAir's playlist address. Top-level consts
are not properties of the vm context, so each check evaluates its expression in it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -151,13 +151,15 @@ After any edit to it:
 ```sh
 npx tsc -p .
 node tests/page-smoke.js
+node --test tests/page-unit.js
 ```
 
 The first type-checks `web/src` (loosely: `strict` is off, and `$` returns `any`). The second
 builds the page as shipped and runs its script against a stub DOM, checking every selector it
 wires at load actually exists. That check exists because a patch once anchored on a deleted
 function, `String.replace` silently matched nothing, and the whole UI died with a
-`ReferenceError` while every server-side test passed.
+`ReferenceError` while every server-side test passed. The third loads the same built script and
+calls its helpers directly (#234): a pure function added to the page gets its check there.
 
 Patching that file by guessing an anchor string has failed repeatedly. Read the exact block first
 (`sed -n 'START,ENDp'`), match it verbatim, and assert the replacement happened rather than hoping.
@@ -168,6 +170,7 @@ Patching that file by guessing an anchor string has failed repeatedly. Read the
 cargo test                # ~80 tests: parsing, filters, retention, schedules, SQL, per-user state
 npx tsc -p .              # type-checks web/src
 node tests/page-smoke.js
+node --test tests/page-unit.js  # the page's own functions, called directly, in a second
 node tests/native-bridge.js  # the page hands playback to a native shell
 node tests/contrast.js    # every theme's palette against WCAG AA
 npx playwright test       # 66 browser tests against a real daemon on fixture feeds