replay: route player input through a command chokepoint (Phase 1)

Reshapes every UI-driven sim mutation to flow through one path so it can be
recorded and replayed later, with behaviour unchanged.

- Command model (lib): Command base + derived types (PlaceBuilding, Demolish,
  RotateInPlace, SetRecipe, SetShipLayout, Set[Site]SplitterFilters,
  ClearBeltTiles, ApplySchematicChoice, Reset), each with a playerId for the
  future-multiplayer shape. PlaceBuilding is atomic (carries optional
  recipe/layout/filters) because deferred commands never return the new
  BuildingId to the caller.
- CommandManager (lib): FIFO queue holding a Simulation&; enqueue + drain.
- Simulation::apply(const Command&): the single chokepoint, dispatching by
  kind to the existing mutators. Mutators stay public (enforced by convention,
  not compile-time, so the test suite keeps driving the sim directly).
- Timing: GameWorldView owns the CommandManager and drains it once per frame in
  onFrame, before the tick batch (runs at 0x too, so build-while-paused is
  preserved). A drained Reset triggers the view reset.
- UI fan-in: GameWorldView enqueues its own input directly; MainWindow and
  SelectedBuildingPanel emit CommandRequestedEvent, which GameWorldView
  subscribes to and enqueues. No UI site mutates the sim directly anymore.
- CommandTest: asserts apply(...) yields byte-identical state to the direct
  mutator path, and that CommandManager drains FIFO through apply.

Full suite green (338 cases / 3353 assertions); determinism double-run still
passes. Design doc updated with the atomic-PlaceBuilding and convention-
enforcement decisions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DUsFgd2Ga6pmLz8giS8WUn

src/ui/GameWorldView.h

@@ -26,10 +26,12 @@
 #include "ExitBuilderModeRequestedEvent.h"
 #include "DebugDrawToggledEvent.h"
 #include "BeamFiredEvent.h"
+#include "CommandRequestedEvent.h"
 #include "SchematicChoiceOption.h"
 #include "SpeedChangeRequestedEvent.h"
 
 #include "entt/entity/entity.hpp"
+#include "CommandManager.h"
 #include "EntitySelectedEvent.h"
 #include "GameConfig.h"
 #include "Rotation.h"
@@ -37,6 +39,7 @@
 #include "TickDriver.h"
 #include "VisualsConfig.h"
 
+struct Command;
 class Simulation;
 class QPainter;
 
@@ -56,7 +59,8 @@ class GameWorldView : public QOpenGLWidget,
                                                   DemolishModeToggleRequestedEvent,
                                                   BlueprintPlacementRequestedEvent,
                                                   ExitBlueprintModeRequestedEvent,
-                                                  SpeedChangeRequestedEvent>
+                                                  SpeedChangeRequestedEvent,
+                                                  CommandRequestedEvent>
 {
     Q_OBJECT
 
@@ -91,6 +95,17 @@ private:
     void handleEvent(std::shared_ptr<const BlueprintPlacementRequestedEvent> event) override;
     void handleEvent(std::shared_ptr<const ExitBlueprintModeRequestedEvent> event) override;
     void handleEvent(std::shared_ptr<const SpeedChangeRequestedEvent> event) override;
+    void handleEvent(std::shared_ptr<const CommandRequestedEvent> event) override;
+
+    // Enqueue a sim command onto the CommandManager (the single mutation path).
+    void enqueueCommand(std::shared_ptr<const Command> command);
+
+    // Enqueue a plain (unconfigured) building placement.
+    void enqueuePlaceBuilding(BuildingType type, QPoint anchor, Rotation rotation);
+
+    // True if the player can currently afford to place one building of `type`.
+    // Used to pre-validate placements whose UI follow-up depends on success.
+    bool canAfford(BuildingType type) const;
 
     void drawTiles(QPainter& painter);
     void drawBuildings(QPainter& painter);
@@ -157,6 +172,11 @@ private:
     const GameConfig*    m_config;
     const VisualsConfig* m_visuals;
 
+    // Funnels all player input into the single Simulation::apply chokepoint.
+    CommandManager m_commandManager;
+    // A Reset command was enqueued; reset the view after the next drain applies it.
+    bool           m_viewResetPending = false;
+
     TickDriver    m_tickDriver;
     QElapsedTimer m_frameTimer;
     std::mt19937  m_rng;