docs(physics): plan the placement production cutover

The continuation executor (5db3de3c) completed the dormant residence
mechanism; the cutover is the campaign leg that makes it production truth.
The committed 8-route inventory maps every duplicate placement authority in
both hosts with exact call chains, confirms the placement-receipt observer
seam is fully built but unattached, and surfaces five pre-cutover gaps the
shipped mechanism cannot yet express (executor-to-channel bridge, atomic
controller/body publication, the 1,880 B/op activation budget, Runtime-side
live-input derivation, the portal-authority adapter). The plan decomposes
the cutover into C0-C5 bisectable slices under the campaign's standing
contract/dual-review/gate discipline, ending at the connected routes and
the user visual matrix that retire AP-1/AD-1.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/plans/2026-08-02-placement-cutover.md

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+# Placement production cutover — campaign plan (2026-08-02)
+
+The final leg of the remaining physics-divergence campaign before AP-22 and
+AD-10: route graphical AND headless production placement through the
+residence + continuation-executor owner (`38fd4b8d` / `30012361` /
+`5db3de3c`), delete the legacy duplicate authorities, and retire AP-1/AD-1
+behind connected + user-visual gates.
+
+**Inputs (read in order):**
+1. [`2026-08-02-runtime-continuation-executor-handoff.md`](../research/2026-08-02-runtime-continuation-executor-handoff.md)
+   — the completed dormant mechanism and its cutover notes.
+2. [`2026-08-02-cutover-route-inventory.md`](../research/2026-08-02-cutover-route-inventory.md)
+   — the full 8-route, both-host call-chain inventory with exact file:line
+   for every duplicate authority to remove. THE map for all slices below.
+3. [`2026-07-31-remaining-physics-campaign-handoff.md`](../research/2026-07-31-remaining-physics-campaign-handoff.md)
+   — the original per-route requirements and prerequisite definitions.
+
+**Standing discipline per slice:** pinned contract → single implementer →
+independent retail-conformance + architecture/adversarial reviews (both must
+PASS on the final diff) → focused + complete Runtime + Release build +
+complete solution gates → bisectable behavior commit (register rows in the
+same commit) → docs/handoff commit. No workarounds; no fused slices.
+
+## Confirmed pre-cutover gaps (from the inventory)
+
+- The executor publishes only generic entity deltas; nothing bridges its
+  completion to `RuntimePlacementProjectionChannel`, so no host can learn
+  "my initial placement committed" through the built observer seam.
+- No atomic controller/body publication owner exists (prerequisite C);
+  App and headless hand-write divergent `PlayerMovementController`
+  construction, and `SubmitPreparedPlacement` requires a canonical
+  `PhysicsBody` that nothing currently publishes atomically.
+- The dormant placement path's 1,880 B/operation (2,048 cap) allocation
+  remains the activation blocker for frame-frequency routes.
+- `Execute`'s live inputs (`UsePositionFromServer`, `PlayerDistance`) are
+  computed by no host; they must derive from Runtime's own character-option
+  and local-player owners.
+- `RuntimePortalPlacementAuthority` has zero producing call sites; the
+  adapter from `RuntimeWorldTransitState` does not exist.
+- The exact-Setup mover chain (`PrepareMover` /
+  `RuntimeSetPositionMoverPreparer.TryBuild` /
+  `IPreparedCollisionSource.ReadSetupCollision`) exists piecewise, unwired.
+- Route-6 split-recovery creates need an effect-replay suppression signal;
+  route-7 needs `TryCommitParent`/`CommitWithdrawal` cancellation-symmetry
+  fixes and host-visible cancellation receipts; headless lacks any
+  parent-realize sequence (pre-existing, adjacent).
+
+## Slices
+
+- **C0 — Runtime bridge + live inputs (dormant).** Publish executor
+  adoption/completion through `Placements` as the receipt stream hosts
+  consume; derive `UsePositionFromServer`/`PlayerDistance` inside Runtime
+  from its own owners (no host-supplied gameplay inputs); wire the
+  exact-Setup mover chain end-to-end for the initial-Create placement; fix
+  the route-7 cancellation asymmetries. Still no production caller.
+- **C1 — atomic controller/body publication (prerequisite C).** One
+  Runtime-owned transaction publishing the exact same canonical body to
+  graphical and no-window controllers, prepared off-canonical, committed
+  atomically, respected by every body writer/binding/clock-epoch/teardown
+  path. The rejected snapshot-lease design stays rejected. Adversarial-gate
+  heavy (the campaign handoff's full list).
+- **C2 — placement allocation budget.** Pool or eliminate the operation/
+  projection envelope allocations on the accepted placement path (root
+  cause, not a raised cap), or obtain explicit user approval for a measured
+  budget. Re-measure; the regression gate keeps the ceiling.
+- **C3 — spawn-frequency cutover: routes 1 + 8.** Flip graphical AND
+  headless initial Create/login registration to
+  `RegisterEntityWithInitialResidence` + executor + placement receipts
+  together; `MaterializeProjection`/`BuildControllerAndCamera`/
+  `SynchronizeLocalPlayer` become projection + acknowledgement only;
+  presentation-only rebucketing (`RebucketLiveEntity` loses `CommitRebucket`).
+  Gates add the exact lifecycle/reconnect connected route.
+- **C4 — remaining routes: 2 (ForcePosition), 3 (portal, with the
+  `RuntimeWorldTransitState` → `RuntimePortalPlacementAuthority` adapter),
+  4 (remote Create/Position; delete `RemoteTeleportController`/`Placement`
+  and the inline MoveOrTeleport duplicate), 5 (projectile authoritative),
+  6 (drops + split-recovery marking), 7 (residual pickup/parent/delete
+  polish).** May land as more than one commit if a route proves large;
+  each sub-landing keeps the full review discipline.
+- **C5 — legacy deletion + closeout gates.** Delete every superseded legacy
+  path; parity tests; exact lifecycle/reconnect + canonical nine-stop
+  connected routes; two-client observation; **user visual matrix** (the
+  campaign's stopping point for user acceptance). Retire AP-1, AD-1,
+  AP-131, AD-60's legacy half, and close #275. Update register/roadmap/
+  milestones/architecture/memory + successor handoff.
+
+After C5: AP-22 (authored collision shapes), then AD-10 (remote
+contact-plane projection), then the campaign's final matrix and ledger
+closeout; vendor Slice 5 resumes.