fix(display): thread-safety for deferred updates, BDF faces and follower image; one refresh default (#652)

- DisplayManager.defer_update()/process_deferred_updates(): one lock around
  every queue mutation (appends from the update thread were lost to the
  render thread's filter/slice reassignments); callables run outside it.
- FontManager and element_style no longer cache BDF freetype.Face objects
  process-wide (load_bdf_face caches them per thread); element_style's LRU
  is locked against get/move_to_end vs eviction races.
- limit_refresh_rate_hz default is one constant, DEFAULT_REFRESH_LIMIT_HZ =
  100 (the template's), for the library options, refresh_hz, the matrix
  guard, Vegas and scroll_config. Previously a missing key capped the panel
  at 90 while pacing assumed 100.
- Sync follower: the TCP thread queues the leader's scroll image; the render
  thread swaps image/array/width in between frames.
- update_display() error log rate-limited (traceback first, then once a
  minute with a count); swallowed DisplayController exceptions log at DEBUG.
- Root display_controller.py runs run.py via runpy.
- stream_manager: correct the RLock release comments; merge duplicate if.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -19,6 +19,13 @@ accepts both, but the store flags the old spelling as deprecated
 
 ## Unreleased
 
+- Display thread-safety and consistency fixes:
+  - `DisplayManager.defer_update()` from a plugin's update thread no longer loses queued updates while the render thread processes the queue; the queue is locked, and the queued callables still run outside the lock.
+  - BDF fonts: `FontManager.get_font()` and `element_style.load_font()` no longer hand one `freetype.Face` to every thread. BDF faces come from `load_bdf_face`, which already caches them per thread; TrueType fonts are cached as before. `element_style`'s font cache is locked (a concurrent eviction could raise `KeyError`).
+  - **Behaviour change:** when `display.hardware.limit_refresh_rate_hz` is missing from config, the panel is now capped at 100 Hz (the config template's value) instead of 90 Hz. Scroll pacing already assumed 100 Hz in that case, so it now matches what the panel does. Configs that set the key (every config migrated from the template) are unaffected.
+  - A sync follower adopts the leader's scroll image between frames on the render thread, instead of the TCP thread swapping the image, array and width while a frame is being drawn.
+  - `update_display()` errors are logged once with a traceback, then at most once a minute with a count, instead of an untraced line every frame. Several swallowed exceptions in `DisplayController` now log at DEBUG.
+  - The repo-root `display_controller.py` now runs `run.py` (the real entry point), so it gets run.py's `-e`/`-d` flags, logging setup and `sys.dont_write_bytecode`.
 - Vegas: a plugin set to `vegas_mode: "static"` pauses the scroll for its turn again. The pause was triggered by peeking at the front of a segment buffer that continuous scrolling (the default) never advances, so a static plugin paused only if it happened to be first, once, at startup, and otherwise scrolled past as ordinary content; swap mode had the same problem for any static plugin not first in its cycle. The render pipeline now marks where each static plugin's turn falls in the strip and the scroll pauses when it gets there. The pause runs the plugin's `display()` under its plugin lock, and a static plugin's content is no longer rendered for the strip.
 
 - The display loop no longer spins at 100% CPU when no enabled mode has anything to show (for example, only a sports plugin enabled in its off-season). After one full rotation of empty modes it checks one mode per second until something shows; live content still takes over at once.