test: quality guard for endpoint artifacts; re-baseline mouse goldens

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,19 @@ All notable changes to this project will be documented here. Format follows
 [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); versioning follows
 [Semantic Versioning](https://semver.org/).
 
+## [Unreleased]
+
+### Changed
+
+- Mouse post-processing pipeline reworked to remove endpoint artifacts:
+  hard forward clip → backtrack-tolerant soft monotonic with tanh
+  overshoot compression (`soften_forward`); tail-drag endpoint snapping →
+  whole-curve smoothstep residual correction (`warp_endpoints`); abrupt
+  start damping → continuous smoothstep damping (`damp_start`);
+  gaussian smoothing now applied to both axes.
+- `tests/unit/data/golden_mouse.npz` re-baselined against the new
+  pipeline (intentional behavior change; scroll goldens unchanged).
+
 ## [0.2.0] - 2026-05-12
 
 ### Changed (breaking)