docs: §4 outdoor full-world flap — onset pinned to building-flood merge (handoff)
Evidence-chain handoff for the outdoor flap investigation: frame-exact
onset (pv-input flood 1->5 + the gl-state doorway-box fingerprint, same
frame), the full probe exoneration chain (camera matrix NaN-free at
6 dp, eye above terrain, cross-frame GL leak refuted, full-screen quad
planes can't cull, MergeNearbyBuildingFloods doesn't touch OutsideView,
ClipFrame capacity clean), the two surviving kill-mechanism suspects
(per-instance clip-slot routing under outdoor roots / terrain UBO
content at draw time), the decisive [clip-route] probe spec, the
user-validated repro protocol, and the probe-semantics gotchas.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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