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/ReplayRecorder.h

@@ -0,0 +1,54 @@
+#pragma once
+
+#include <cstdint>
+#include <fstream>
+#include <string>
+
+#include "Tick.h"
+
+struct Command;
+
+// 64-bit hash (16-char hex) over the *.toml files in configDir. Stored in the
+// replay header and recomputed on playback to detect a config mismatch.
+std::string computeReplayConfigHash(const std::string& configDir);
+
+// Writes a replay file as the game runs (see docs/replay_design.md). The format
+// is line-oriented append-friendly text: a small keyed header, then one line per
+// command (tick-tagged) interleaved with RNG-state checksum lines for desync
+// detection. Each line is flushed so a crash mid-run still leaves a valid partial
+// file.
+//
+// One file = one run between Reset boundaries; startNewRun() closes the current
+// file and opens a fresh one.
+class ReplayRecorder
+{
+public:
+    // configDir: hashed (its *.toml files) into the header for config-mismatch
+    //   detection on playback. outputDir: where .replay files are written.
+    ReplayRecorder(std::string configDir, std::string outputDir);
+    ~ReplayRecorder();
+
+    ReplayRecorder(const ReplayRecorder&) = delete;
+    ReplayRecorder& operator=(const ReplayRecorder&) = delete;
+
+    // Close any current file, then open a fresh one (named <timestamp>_<seed>),
+    // write the header, and record an initial tick-0 checksum. A run boundary.
+    void startNewRun(unsigned int seed, std::uint64_t initialRngFingerprint);
+
+    // Append one command line tagged with the tick it was applied at, followed by
+    // the post-apply RNG checksum.
+    void recordCommand(Tick tick, const Command& command, std::uint64_t rngFingerprint);
+
+    // Append a periodic RNG checksum line.
+    void recordChecksum(Tick tick, std::uint64_t rngFingerprint);
+
+    void close();
+    bool isOpen() const;
+    const std::string& currentFilePath() const;
+
+private:
+    std::string   m_configDir;
+    std::string   m_outputDir;
+    std::string   m_filePath;
+    std::ofstream m_stream;
+};