1.3.1-beta release - #15

…-load bg leak

Three deck-lifecycle defects (issues StreamController#11, StreamController#12, StreamController#15):

- StreamController#11: on a background-video page update_all_inputs skipped ALL key device
  writes (the per-frame loop paints keys) -- but the loop deliberately
  never repaints fully-opaque keys (their tile hides the video), so those
  never received their FIRST paint after a page switch: the device kept
  showing the previous page's content there until a keypress. The bg-video
  branch now update()s keys whose composed color is fully opaque; their
  tile hides the video, so the write cannot disturb it.

- StreamController#12: close() step 6 ran plugin teardown hooks unbounded on the DeckClose
  thread. A wedged hook (pulsectl precedent) stranded steps 7-9 forever --
  media sweep, fallback deck.close and deregistration never ran (the
  unplug leak reintroduced) and _closing=True made a retry a permanent
  no-op. Step 6 now runs on a daemon thread with a bounded join
  (TEARDOWN_JOIN_TIMEOUT_S, class-level for the harness); on timeout the
  hook thread is abandoned with a loud error and teardown completes.

- StreamController#15: close() neither bumped _page_load_generation nor cancelled
  _bg_future, so an in-flight load that passed the _closing gate could
  attach a fresh BackgroundVideo (cv2 capture + registry ref + builder
  thread) AFTER step 7's resource sweep -- leaked until process exit.
  close() now invalidates the generation under _page_gen_lock and cancels
  the pending background future first thing.

tests/scenario_deck_lifecycle_trio.py red-checks all three (writer stopped
and drained for determinism on the paint check; the wedge is a blocking
_teardown_actions with the timeout tightened; gen invalidation is checked
with a pre-close generation capture).

…aque UI push (review round 1)

Follow-up to the deck-lifecycle trio, addressing MR !42 review round 1.

- StreamController#15 (residual): the gen-bump + _bg_future.cancel() in close() only cover a
  load_background that has NOT yet reached its _page_is_current(gen) gate. A
  load already PAST that gate -- parked inside the seconds-long prebuild --
  would still attach a fresh BackgroundVideo (cv2 capture) onto
  self.background.video AFTER close()'s step-7 sweep, leaking until process
  exit (the exact unplug-mid-switch leak StreamController#15 targets, via a different
  schedule). Closed with belt-and-suspenders: apply_prebuilt now re-checks
  _closing (set at the top of close(), before the sweep) and, when closing,
  discards the orphaned payload's resources instead of attaching it; and the
  step-7 background sweep runs under _background_load_lock so it cannot
  interleave with an in-flight attach. The _closing re-check is the
  load-bearing guard; the lock guarantees the sweep observes and releases the
  final background object rather than racing a concurrent set_video.

- StreamController#11 (nit): opaque keys called update() (which paints device AND app
  preview) and then hit the unconditional UI-only mirror -- a redundant second
  UI push per opaque key. update() + continue now handles both; non-opaque
  keys still get the UI-only mirror (their device paint comes from the video
  loop).

- StreamController#12 (doc): documented that the abandoned-teardown-thread residual is
  inherent to abandon-on-timeout, and that the wedge parks in
  clear_action_objects (before _teardown_actions's resource cleanup), so the
  residual surface is narrow -- a note for any future reordering.

Tests (scenario_deck_lifecycle_trio.py):
- New check_close_load_race: parks a load past its gen-gate, runs close()'s
  sweep, releases the load, asserts NO BackgroundVideo attaches on the closed
  controller and the orphaned payload was close()d. Red-checked (without the
  fix the leak reproduces); stable across repeated runs.
- Strengthened check_opaque_initial_paint: asserts the opaque key's device
  write carries the NEW page's opaque-color bytes (journal content hash),
  not just that a write happened, plus a differential so the assertion can't
  pass vacuously.

Harness: 89/89 PASS.