Resolves the 5 /code-review high findings on this branch:
- a11y sweep: extend aria-label to the remaining icon-only Plex card buttons the
first pass missed — PlexPosterCard Info, SeasonCard watched-toggle + add-season
(EpisodeCard already had them). "Fix a principle everywhere, in one sweep."
- new shared lib/parseId.ts `parsePositiveIntId`, used by BOTH readSelectedId
(now guarding the stored ?pl fallback the same as the URL — was unguarded) and
plexSubUrl's ?v=playlist decode; removes the hand-duplicated guard.
- PAGE_KEY exported from navigationInit and imported by NavigationProvider (was
defined in both).
- hoist a `watchedLabel` const per card so title + aria-label can't drift.
+8 tests (parseId unit + guarded-stored ?pl); full FE gate green (tsc/eslint/
prettier/knip, 317 vitest).
The remaining E4 deep-review deferred gaps, in one sprint:
- readSelectedId split into playlistsInit.ts (react-refresh-clean, testable) —
?pl accepted only as a positive integer; empty/0/negative/fractional/non-numeric
fall back to the stored selection; null when neither is present.
- useUrlMirror: mounts write the param, a same-serialized rerender does NOT
re-fire (stable dep), a null value clears the key, other params preserved.
- usePref: a pending debounced write is FLUSHED on unmount (not dropped); an
unmount with nothing pending stays silent.
20 new test cases; full FE gate green (tsc/eslint/prettier/knip, 309 vitest).
peter