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BT411/scratchpad
Joe DiPrimaandClaude Opus 5 eebe7e61a4 gotcha #28: hand-composing an engine-derived transform reads a stale cache (replicant-only)
The #141 bug class, written up so it is not re-introduced.  GetSegmentToEntity
recomputes ONLY when segmentModified is set; JointedMover::GetSegmentToWorld is
what sets it -- and the binary's own GetMuzzlePoint @004b9948 goes through it
(FUN_00424da8), so every muzzle query in the 1995 image performs the
joints->segments refresh.  Four port sites hand-composed instead, one of them
commented "the faithful FUN_004b9948".

Records the four rules the investigation actually cost:
 (a) never hand-compose; call GetSegmentToWorld
 (b) never force the dirty flag to fix a stale read -- that stand-in scored
     IDENTICALLY to the faithful fix while patching only one consumer
 (c) "peer POV only" geometry bugs = suspect a cache the local render pass
     refreshes for free, before suspecting replication (it was provably fine)
 (d) a partial-looking score: check PREFIX vs interleaved before calling it
     partial -- these were a clean prefix ending when the peer first had a
     twist to carry, so the fix was complete and "64% fixed" was wrong
 (e) the probe trap: one shared static sampled every Nth call hides one of two
     alternating instances entirely

#141 closed with the full write-up; #148 filed for the torso replication
cadence (13 records in a 5-minute run) which is a separate, real problem and
likely bears on #37 and #70.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018SgmXGNMXavXiafKXf9MDC
2026-08-08 09:29:47 -05:00
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