Merge remote-tracking branch 'origin/claude/frame-timing-harness' into claude/scan-order-compensation

# Conflicts:
#	src/display_manager.py

CHANGELOG.md

@@ -19,6 +19,15 @@ accepts both, but the store flags the old spelling as deprecated
 
 ## Unreleased
 
+- `src.common.frame_timing` -- times every frame the display presents, whoever
+  drew it, and writes cumulative counters to `/dev/shm`. Two tools read it:
+  `scripts/frame_soak.py` judges a running service (late frames, freezes,
+  where the time goes), and `scripts/render_bench.py` judges the hardware and
+  render path alone on a synthetic strip. Both fail a run above 0.1% late
+  frames, and both call a loop that never waited for the panel NOT LOCKED. A
+  stall watchdog logs the stack of whatever holds a scroll up for 250 ms or
+  more. See `docs/SCROLL_PERFORMANCE.md`, "Soaking a rig".
+
 - The web service (`ledmatrix-web`) logs through `src.logging_config` like the
   display service, so `journalctl -p err -u ledmatrix-web` works. Successful
   GET/HEAD/OPTIONS requests (the UI's polling) are logged at DEBUG instead of