feat(runtime): bridge executor completion to the placement stream

Cutover slice C0 (docs/plans/2026-08-02-placement-cutover.md): the seam
work that lets C3 flip hosts onto a complete receipt stream instead of
growing one mid-cutover. The executor's Released exit now publishes an
acknowledge-only ExecutorCompleted receipt through the one placement
projection stream — registered before observer dispatch, correlated to
the full execution receipt, reaped exactly once on acknowledgement/
discard/session-clear, and counted in the convergence ledger. All three
production placement sinks acknowledge-and-ignore the new kind via early
returns proven behavior-preserving for every existing kind; without them
the first such receipt at cutover would permanently wedge the exact-head
FIFO behind sinks that return false. Provably inert today: the publisher
has no production caller.

Execute's live inputs now derive from Runtime's own owners bound at
GameRuntime construction: UsePositionFromServer is retail's exact
autonomy_level != 2 (CommandInterpreter::UsePositionFromServer
0x006B3B40, startup-only knob), and PlayerDistance uses the live movement
controller's position with a null-safe fallback to the caller struct —
never a fabricated origin. TryPrepareAndSubmitAuthoredPlacement chains
the prepared-collision Setup read through PrepareMover to submission with
zero validation-semantics changes. TryCommitParent and CommitWithdrawal
gain the sibling cancellation flow (residence + ordinary placement
family); TryCommitParent deliberately omits LeaveWorld — retail's
set_parent performs its single gated leave_world (0x00515A90) and a
second would have no counterpart.

Not fully dormant: the two cancellation fixes change Runtime paths
production already calls (today as no-op-adjacent hardening, since
nothing upstream begins a residence yet); everything else is reachable
only by tests. Reviewed: retail-conformance PASS + architecture/
adversarial PASS after one fix round (sink wedge, completion-receipt
lifecycle, null-controller distance). Runtime 921/921; complete Release
solution 10,716 passed / 4 intentional skips.

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

src/AcDream.App/World/LiveEntityRuntime.cs

@@ -946,6 +946,19 @@ public sealed class LiveEntityRuntime : ILiveEntityRadarSource
             return true;
         }
 
+        if (projection.Kind is RuntimePlacementProjectionKind.ExecutorCompleted)
+        {
+            // F1: acknowledge-and-ignore, same as Discard. Must NOT fall
+            // through to the record-lookup/spatial-load gates below - those
+            // legitimately reject for reasons unrelated to this receipt (no
+            // sidecar yet, destination backend not loaded), and a false
+            // return here wedges the whole ordered placement stream at the
+            // FIFO head (RuntimePlacementProjectionSubscription's contract).
+            // Provably inert today: PublishExecutorCompletion has zero
+            // production callers.
+            return true;
+        }
+
         RuntimePlacementProjectionToken token = projection.Token;
         if (!TryGetRuntimePlacementProjectionRecord(
                 token,