docs: C4 route 4b scoping — split three ways, and two corrections

Scoping at 44830a0e puts 4b at 1,300-2,200 production lines (centred ~1,700)
plus ~2,500-3,500 lines of test work — 4-6x route 4a and ~2x route 2, the two
largest landings in this campaign, which took 4 and 5 review rounds. Split into
4b-1 (infrastructure, no behaviour change), 4b-2 (far branch), 4b-3 (teleport
and cell-less, with the ~739-line class deletions). 4b-1 stays separate
regardless of appetite for landings.

Corrects two errors in documents from yesterday:

AP-135 does NOT retire with 4b. Its own condition is retirement with the
free-fall sweep gate, which 4b does not touch, and its sites are the airborne
no-op branches — 4a-owned dispositions. The trap is that its two writes sit
inside OnPosition, which 4b rewrites heavily.

Retail has exactly ONE ConstrainTo on the remote arm (@0x00454272); all three
nonzero-returning MoveOrTeleport branches funnel through it. My route-4 scoping
implied a distinct remote-teleport arming site. There is none, so 4b must not
add a second one — the post-operation arm 4a introduced becomes the only arm.

Records a new failure mode 4b must not create: a DeferredCell park WITHDRAWS the
entity (InWorld false, Active cleared, clock suspended, residency dropped), and
Forget-on-every-accepted-Position kills the park without restoring any of it. If
the next packet classifies Interpolate, no placement runs and the remote stays
withdrawn indefinitely — invisible AND intangible, the #184 class through a
third door. Direction: refuse rather than park; the next packet is the retry,
because remote Positions are a 5-10 Hz stream.

Two transfer errors named explicitly so they are not repeated: do not port route
2's re-issue funnel (re-issuing a superseded pose is wrong for a repeated
stream), and do not port its ack machinery (retail's remote arm has no
SendPositionEvent).

Also records that remotePlacementRequired fires for every non-visible remote on
the graphical host — a routine hot path, not a teleport rarity — and that
deleting the legacy blocks removes the only handler for null/Rejected*, which
during the login window is every remote packet.

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

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

@@ -297,8 +297,23 @@ same commit) → docs/handoff commit. No workarounds; no fused slices.
       own live evidence, not a silent convergence.
     - Register row **AP-135** (the airborne no-op's retained acdream
       bookkeeping: the server cell id for the free-fall sweep gate, and the
-      last-server-position sample) retires with 4b's transition machinery, not
-      before.
+      last-server-position sample) — **CORRECTED 2026-08-04: this row does NOT
+      retire with 4b.** Its own stated condition is retirement together with the
+      free-fall sweep gate (`RuntimeRemotePhysicsUpdater.cs:342`), which 4b does
+      not touch, and its sites are the airborne no-op branches — 4a-owned
+      dispositions, not 4b's far-snap/teleport/cell-less. The trap is that those
+      two writes sit physically inside `OnPosition`, which 4b rewrites heavily,
+      so an implementer will assume they go. They stay. See
+      [`2026-08-04-c4-route-4b-scoping-and-split.md`](../research/2026-08-04-c4-route-4b-scoping-and-split.md).
+    - **4b is itself split into 4b-1 / 4b-2 / 4b-3** (2026-08-04). Scoping put
+      4b at 1,300-2,200 production lines — 4-6x route 4a — plus ~2,500-3,500
+      lines of test work. 4b-1 is infrastructure with no remote behaviour change
+      (the per-entity placement owner, the service-window guard, the
+      refuse-rather-than-park policy, N3's headless `RetryPending` pump); 4b-2 is
+      the far branch alone; 4b-3 is teleport/cell-less and the ~739-line class
+      deletions. 4b-1 stays a separate landing regardless: it is where the
+      park-withdraws-the-entity failure mode is decided, and it must not be
+      reviewed alongside a large deletion.
   Note the route-4 Create half is ALREADY DONE (C3b/C3c); the remaining work is
   steady-state remote Position plus the deletions. AP-131 is NOT retired by
   either sub-slice — see the scoping doc for why route 4 alone cannot.