Root cause (pinned live, flap-churn.log at the Holtburg cottage doorway): the physics
body is byte-stable at rest (rawPlayer = 1 distinct value), but
PlayerMovementController.ComputeRenderPosition's Lerp(prev, curr, alpha) dithers the
render position by microns — the two physics-tick snapshots lag the settled body
(per-frame resolve edge-settles the resting sphere against the doorframe after the last
tick wrote curr) while the leftover-accumulator alpha varies every frame. The grazing-
doorframe camera-collision sweep (PhysicsCameraCollisionProbe.SweepEye) amplifies that
~1000x into a ~1.3 mm eye jitter (eye 17 distinct, RenderPosition 15 distinct) that trips
the PortalVisibilityBuilder clip -> the standing-still flicker (blue void / grass over the
cellar entrance) the user reported.
Fix: at rest (body velocity below RestVelocityEpsilonSq) render AT the authoritative
byte-stable body position instead of interpolating between two stale tick snapshots, so the
camera's pivot input is byte-stable and the sweep output stops jittering. Mirrors retail (a
resting object renders bit-stable) + the boom convergence snap
(RetailChaseCamera.ApplyConvergenceSnap, d2212cf), one layer earlier. Sub-tick interpolation
is preserved during motion (velocity above epsilon).
This SUPERSEDES the committed bounded-propagation plan: the live pin proved ZERO portal
re-enqueue churn during the flap (maxPop=1 across 13k oscillating frames; 0/63k reciprocals
ever clipped empty), so the flap was never the churn the spec hypothesized. The
ACDREAM_PROBE_PORTAL_CHURN apparatus did its job (refuted the hypothesis before the wrong
fix was built); plan/spec/memory updates to follow.
TDD: extracted the rest-snap into an internal-static pure ComputeRenderPosition; RED rest-
snap test (stale prev!=curr + varying alpha dithers) -> GREEN after the gate; motion test
guards interpolation; precondition test confirms a settled body's velocity is below the
gate threshold. 29 controller+cellar + 62 camera+portal tests green, no regression.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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