Replay: deterministic record & playback (#4)

Add deterministic record/playback for a run.

Recording captures `(seed, config hash, ordered tick-tagged commands)` and re-simulates on playback — no state snapshots. `DotaFactory.exe --replay <file>` re-plays a recorded run view-only with manual speed/pause.

Reviewed-on: #4
Co-authored-by: Malte Langkabel <malte.langkabel@gmail.com>
Co-committed-by: Malte Langkabel <malte.langkabel@gmail.com>

src/lib/sim/CommandManager.cpp

@@ -0,0 +1,92 @@
+#include "CommandManager.h"
+
+#include <utility>
+
+#include "Command.h"
+#include "ReplayRecorder.h"
+#include "Simulation.h"
+#include "Tick.h"
+
+namespace
+{
+// Periodic RNG checksum cadence (see docs/replay_design.md "Cadence").
+constexpr Tick kChecksumIntervalTicks = 30;
+}  // namespace
+
+CommandManager::CommandManager(Simulation& simulation)
+    : m_simulation(simulation)
+{
+}
+
+CommandManager::~CommandManager() = default;
+
+void CommandManager::enqueue(std::shared_ptr<const Command> command)
+{
+    if (m_replayMode)
+    {
+        return;  // playback is driven by the recorded stream; ignore live input
+    }
+    if (command)
+    {
+        m_queue.push_back(std::move(command));
+    }
+}
+
+void CommandManager::drain()
+{
+    // Apply in FIFO order. A queued ResetCommand reinitializes the simulation in
+    // place; the reference stays valid and any commands after it apply to the
+    // fresh state.
+    for (const std::shared_ptr<const Command>& command : m_queue)
+    {
+        if (command->kind == CommandKind::Reset)
+        {
+            m_simulation.apply(*command);
+            if (m_recorder)
+            {
+                // Restart is a file boundary: a fresh file with the new seed.
+                m_recorder->startNewRun(m_simulation.getSeed(),
+                                        m_simulation.rngFingerprint());
+            }
+        }
+        else
+        {
+            // Commands drain before the tick batch, so currentTick is the count of
+            // completed ticks the command is pinned to.
+            const Tick tick = m_simulation.currentTick();
+            m_simulation.apply(*command);
+            if (m_recorder)
+            {
+                m_recorder->recordCommand(tick, *command, m_simulation.rngFingerprint());
+            }
+        }
+    }
+    m_queue.clear();
+}
+
+bool CommandManager::hasPending() const
+{
+    return !m_queue.empty();
+}
+
+void CommandManager::setRecorder(std::unique_ptr<ReplayRecorder> recorder)
+{
+    m_recorder = std::move(recorder);
+    if (m_recorder)
+    {
+        m_recorder->startNewRun(m_simulation.getSeed(), m_simulation.rngFingerprint());
+    }
+}
+
+void CommandManager::setReplayMode(bool replayMode)
+{
+    m_replayMode = replayMode;
+}
+
+void CommandManager::recordTickCheckpoint()
+{
+    if (m_recorder && (m_simulation.currentTick() % kChecksumIntervalTicks == 0))
+    {
+        m_recorder->recordChecksum(m_simulation.currentTick(), m_simulation.rngFingerprint());
+    }
+}