docs(physics): record flat cutover rollback and evidence

Pin the exact I6 production-cutover revert command before visual acceptance, distinguish observer-heavy connected metrics from the production-like dense-Arwic run, and preserve the strict publication/referee evidence.

Co-authored-by: Codex <codex@openai.com>

docs/research/2026-07-25-slice-i6-flat-production-cutover.md

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+# Slice I6 — flat production collision cutover
+
+## Result
+
+Commit `068a06518dd710ca5e7f166754cbb7789ca1ed0f` makes the immutable
+prepared collision representation authoritative for gameplay. The parsed DAT
+graph remains temporarily resident only as the automated differential referee.
+
+Production now:
+
+- creates its `PhysicsDataCache` through the explicit production factory;
+- fails publication when a required prepared GfxObj, Setup, CellStruct, or
+  EnvCell topology record is genuinely absent;
+- accepts idempotent publication when that flat asset is already resident;
+- returns flat results even when the graph referee disagrees;
+- uses flat containment for the unified cell graph;
+- uses flat polygon tables for nearest indoor floor lookup;
+- derives live/static BSP shape bounds and camera diagnostics from flat data.
+
+Graph-only cache construction remains an explicit test/tooling oracle seam
+until the post-acceptance deletion commit.
+
+## Exact rollback
+
+```text
+git revert 068a06518dd710ca5e7f166754cbb7789ca1ed0f
+```
+
+Do not revert the I3 package schema, I4 traversal, or I5 dual-publication
+commits.
+
+## Automated conformance
+
+- Release build: pass.
+- Complete Release solution: 8,402 passed / 5 skipped.
+- Warm flat traversal: 0 B.
+- Reused resolver scratch across player, remote, projectile, camera, and
+  grounded mover families: 0 B/resolve.
+- Retained render hot-path allocation fixtures: pass.
+- Flat-authoritative mismatch fixture proves the graph cannot change gameplay.
+- Production publication fixtures prove missing prepared data fails and an
+  already-resident prepared asset remains idempotent.
+
+## Connected strict-publication/referee gate
+
+Evidence:
+`logs/connected-dense-town-20260725-165758.report.json`.
+
+- PASS with graceful authoritative logout and `WM_CLOSE`.
+- Dense Arwic: 15,530 entities / 111 animated.
+- Collision referee: 46,309 queries, 46,309 exact matches.
+- Mismatches: 0.
+- Referee faults: 0.
+- Mismatch artifacts: 0.
+- Stable cell residency: 292 graph / 292 flat during the referee window.
+
+The first strict attempt correctly exposed an idempotency-contract defect:
+`LiveCollisionAssetPublisher` passed `null` after finding the prepared asset
+already resident, and the guard interpreted that as absent. The root fix makes
+the cache distinguish “already published” from “not provided”; strict missing
+package data still fails.
+
+## Production-like performance check
+
+The normal connected gate intentionally enables the complete current-path
+render oracle and allocates about 10.8 MiB/frame in dense Arwic. It is a
+correctness observer, not a production performance measurement.
+
+A separate Release run used the same dense-Arwic arrival and six-second camera
+turn with:
+
+- uncapped rendering;
+- no lifecycle artifact directory;
+- no current-path render oracle;
+- no collision referee;
+- no runtime counter attachment.
+
+Stable result:
+
+- about 190–200 FPS;
+- CPU p50 about 5.0 ms;
+- CPU p95 about 5.9–7.3 ms;
+- GPU p95 about 2.1 ms;
+- update p95 about 1.4–1.8 ms;
+- roughly 8% total-machine CPU;
+- working set about 1.12 GiB;
+- private bytes about 1.41 GiB;
+- warm allocation about 84.6 KiB/frame in the dense scene.
+
+The parsed graph is still resident in those memory figures. I6 graph removal
+must reduce that footprint and prove stable production graph counts are zero.
+
+## Acceptance boundary
+
+The automated cutover gate is complete. Before deleting the referee and parsed
+graph, the user must verify outdoor/indoor movement, doors, ramps/stairs,
+jump/fall, camera-wall collision, object interaction, combat/projectiles, and
+portal/reconnect behavior on the cutover commit.