Score exposure sweeps by LED spline quality

docs/implementation-plan.md

@@ -393,6 +393,12 @@ a named invariant that the native runtime cannot protect yet.
   correspondence requires coded or otherwise stable LED identity; uncoded
   repeated lights remain curve constraints until the global residual solver
   resolves them.
+  Exposure/gain sweeps must optimize recovered spline quality, not generic
+  contrast or brightness. `MimirLedSplineQualityScorer` scores each setting by
+  detected LED count, curve coverage, spacing coherence, smoothness, exposure
+  fitness, and saturation penalty. `--led-spline-quality-sweep-smoke` proves
+  the selector chooses the balanced setting over both underexposed missing-LED
+  detections and overexposed saturated halos.
   Phase 6 program-output receipts are also structurally complete: Fensalir
   publishes the final program surface through named shared D3D12 texture/fence
   resources, the OBS plugin consumes that surface with an explicit D3D12-to-

docs/sensor-fusion-architecture.md

@@ -33,6 +33,9 @@ flowchart TD
 - Stable LED index identity requires temporal/color/address coding or another
   correspondence source; uncoded identical lights are spline constraints, not
   metric depth authority.
+- Exposure/gain sweeps optimize recovered spline quality: detected LED count,
+  curve coverage, spacing coherence, smoothness, exposure fitness, and
+  saturation penalty. Bright clipped blobs are not good evidence.
 - The first camera-rig solver fits bounded camera translation updates from a
   scene-anchored LED curve by minimizing ray-to-curve distance. Rotation,
   intrinsics, and distortion are future owners.