test: golden-master regression for scenario #0 (#38)

tests/baselines/regenerate_scenario_0.py

@@ -0,0 +1,46 @@
+"""Regenerate the scenario #0 regression baseline (issue #38).
+
+Run from the repository root *after a deliberate physics change* (and review the
+resulting diff before committing):
+
+    PYTHONPATH=. python tests/baselines/regenerate_scenario_0.py
+
+The baseline is tied to the current repository + ActiveRocketPy submodule state,
+so it must be regenerated whenever the rocket physics is intentionally updated.
+"""
+
+import json
+from pathlib import Path
+
+from tests.test_scenario0_regression import (
+    AGENT_KWARGS,
+    DOWNSAMPLE_STRIDE,
+    post_launch_positions,
+    run_scenario_0,
+)
+
+OUTPUT_PATH = Path(__file__).parent / "scenario_0.json"
+
+
+def main():
+    positions, popped = run_scenario_0()
+    baseline = {
+        "scenario_number": 0,
+        "random_seed": 0,
+        "agent": "AttitudeRateControlAgent",
+        "agent_kwargs": AGENT_KWARGS,
+        "downsample_stride": DOWNSAMPLE_STRIDE,
+        "num_steps_full": int(positions.shape[0]),
+        "popped_count": int(popped),
+        "rocket_position_downsampled": post_launch_positions(positions).tolist(),
+    }
+    with open(OUTPUT_PATH, "w", encoding="utf-8") as output_file:
+        json.dump(baseline, output_file, indent=2)
+    print(
+        f"wrote {OUTPUT_PATH} "
+        f"(steps={baseline['num_steps_full']}, popped={baseline['popped_count']})"
+    )
+
+
+if __name__ == "__main__":
+    main()