Hold proxy in hidden position when no remote

Add a temporary in-cell holding fallback for the single placed proxy actor when no valid same-cell remote player is available. Introduces kProxyHiddenHoldingPosition, ProxyLifecycleState, RemotePlayerSelection, MoveProxyToHoldingPosition and RestoreProxyForRemotePlayer, plus selection/state-tracking and throttled logs. The controller now moves the proxy to the hidden position on disconnect, disappearance, or cell-mismatch and snaps it back when a valid same-cell remote appears. Documentation and dev log updated to describe the lifecycle and rationale (docs/architecture.md, docs/dev-log.md, protocol/player-sync.md).

docs/architecture.md

@@ -30,6 +30,10 @@ both send and receive paths:
     Proxy visual updates are independent from local movement log throttling:
     normal movement is smoothed toward the latest target, while cell changes,
     worldspace changes, and teleports snap directly.
+12. When the selected remote player is missing, disconnected, or not in the same
+    test cell, the game-thread proxy controller moves the single placed proxy to
+    a hidden holding position inside `F4TTestCell01` until a valid same-cell
+    remote player is available again.
 
 The Fallout 4 plugin still does not dynamically spawn remote actors.
 
@@ -48,6 +52,8 @@ The native plugin is responsible for:
 - Storing assigned and remote `playerId` state internally
 - Moving the single placed test proxy actor from remote-player state on the game
   thread
+- Holding that proxy actor at a hidden in-cell position when no valid same-cell
+  remote player should be represented
 
 Planned later:
 

docs/dev-log.md

@@ -837,6 +837,51 @@ Player position: X=2048.00, Y=2048.00, Z=0.00, AngleZ=0.00
 
 ---
 
+## 2026-06-02 - Proxy Lifecycle Holding
+
+### What Changed
+
+- Added controller-local lifecycle state for the single placed proxy actor.
+- Added a temporary hidden holding position inside `F4TTestCell01` for cases
+  where no valid same-cell remote player should be represented.
+- Moved the proxy to the holding position when the represented remote player
+  disconnects, disappears from remote-player state, or leaves the local test
+  cell.
+- Restored representation by snapping the proxy to a valid same-cell remote
+  player once before resuming existing smooth movement.
+- Kept disconnect, no-remote-player, and cell-mismatch logs transition-based or
+  throttled so the log does not spam every update.
+
+### What Worked
+
+- Actor/reference access remains inside `F4TProxyActorController` on the
+  game-thread update path.
+- The networking protocol, Python server, and fake client remain unchanged.
+- Existing smooth movement, special movement snapping, and sneak-state
+  observation remain in place for valid same-cell remote players.
+
+### What Broke
+
+- Nothing recorded during implementation.
+
+### Notes
+
+- This milestone deliberately does not call `Disable()`, `Enable()`,
+  `SetAlpha()`, invisibility APIs, or animation graph APIs.
+- Dynamic spawning, multiple proxy actors, combat, inventory, quest, settlement,
+  weapon/projectile, interaction, and animation sync remain out of scope.
+- The holding position is a prototype-safe fallback until a hide/disable path is
+  validated for the persistent placed proxy reference.
+
+### Next Steps
+
+- Test single-client, two-client, disconnect, cell-leave, and return/reconnect
+  flows in `F4TTestCell01`.
+- If the holding fallback proves stable, separately validate whether a true
+  hide/disable path is safe for the placed proxy reference.
+
+---
+
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