acdream/docs/research/2026-08-07-s6-perfectclip-containment-contract.md

S6 contract (Campaign S) — contain the undecodable PerfectClip TOI tails (AP-83 / AP-91)

Date: 2026-08-07. Implementer: one Sonnet agent, after S4b lands. Review: one Opus pass (small slice). No visual gate — fully automated.

What this is, and is not

AP-83 and AP-91 record that the PerfectClip time-of-impact tails in CylCollideWithPoint and SphereCollideWithPoint/FindSphereTimeOfCollision (TransitionTypes.cs) were decoded via ACE because the retail x87 sequences do not decompile. There is no retail text to port — this slice does NOT "fix" them. The deliverable is proof about reachability plus a loud guard, so the rows become auditable instead of aspirational (the AP-22 resolution shape).

Premise correction, pinned at scoping — the rows' "no mover sets

PerfectClip" is FALSE as stated

PhysicsCameraCollisionProbe.cs:69 sets ObjectInfoState.PerfectClip on the CAMERA mover (faithful to retail's camera flags). So containment must be proven as: the camera's resolve can never reach the Cyl/Sphere PerfectClip TOI tails. Candidate arguments to verify (do not assume any):

1. The viewer exemption block in FindObjCollisions/CollisionExemption (viewer-vs-creature skip, CollisionExemption.cs:83-85 region) — does it skip ALL shadow objects for a viewer mover, or only creatures? A static prop with CylSpheres in the camera's sweep would reach the tail if not.
2. Whether the camera resolve enumerates shadow objects at all (retail's update_viewer sweep may be environment-only — check our port's call shape at the camera probe's ResolveWithTransition arguments). If BOTH arguments fail — the camera genuinely can reach a Cyl/Sphere TOI tail — that is a FINDING, not a failure: the ACE-derived math is then LIVE production code for the camera, and the rows get rewritten to say so with the camera named as the reachable population (severity: camera-feel only).

Deliverables

1. Reachability proof or refutation, written into a short doc: for each of the two tails, the exact call chain from every PerfectClip-setting mover (grep-proof of the full setter population first — today it is the camera probe alone, verify), and where each chain is cut (file:line), or not.
2. The loud guard: at the head of each TOI tail, a debug-only assertion (or diagnostics counter + one-shot log, matching house style for invariants) that fires if the tail executes with a mover whose reachability was proven impossible — so a future flag change cannot silently start executing ACE-derived math nobody re-verified. If the camera IS reachable, the guard instead records the tail as camera-live (counter, not assert).
3. Tests: one per tail driving the production resolve with a PerfectClip mover against a Cyl/Sphere-shaped shadow entity, asserting whichever reachability the proof established (reached → the guard counter increments and the ACE-derived result is pinned as a golden; unreached → the exemption cuts it and the guard stays silent). Sabotage: disable the exemption that cuts the chain and watch the reachability flip.
4. Register rewrite text for AP-83/AP-91 handed to the session lead (rows stay ACTIVE either way — the math remains ACE-derived — but their population claim becomes measured).

Scope — OUT

Any change to the TOI math itself. The camera's flag set (retail-faithful). Register/ISSUES edits (session lead).

Acceptance

Scoped build/test green (Core + Core.Tests; clean-room for the verdict run); sabotage reported verbatim; nothing committed. Absolute paths, no subagents, contradictions → STOP.