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).
Split the two URL-derived nav seeds out of NavigationProvider into
navigationInit.ts so they're unit-testable and the provider stays
react-refresh-clean (component-only exports). channelViewFrom also dedups the
identical _chan/?chan resolve the channelView seed and the onPop handler each
hand-rolled — locking the S1 fix (a popstate on a URL-only bookmark entry must
restore the channel from ?chan, not close it). Pure code motion.
Tests: the full loadInitialPage precedence matrix (?page > ?v > ?pl >
filters/?chan > stored landing > feed, with the beats-a-lower-param cases) and
channelViewFrom (_chan+name, ?chan fallback, state-over-url, closed → null).
15 tests; full FE gate green (tsc/eslint/prettier/knip).
peter