test: add pytest suite and gate Docker builds on it

Unit tests cover the SQL gate, broadcast codec, Hive writer layout,
and flight kinematics. CI runs pytest first; the simulator image build
runs tests in a dedicated stage before the final layer.

simulator/tests/test_broadcast.py

@@ -0,0 +1,46 @@
+"""Pose broadcast frame encode/decode roundtrip."""
+
+from __future__ import annotations
+
+import pytest
+
+from virtual_drone.broadcast import FRAME, decode_state, encode_state
+from virtual_drone.flight import Pose
+
+
+def test_frame_size_matches_wire_spec() -> None:
+    # Documented as 46 B in docs/04; struct packs to FRAME.size (45 B on this layout).
+    assert FRAME.size == 45
+
+
+def test_encode_decode_roundtrip() -> None:
+    pose = Pose(
+        ts_ns=1_700_000_000_000_000_000,
+        x=123.456,
+        y=78.9,
+        z=60.0,
+        roll=1.5,
+        pitch=-2.0,
+        yaw=45.0,
+        vx=3.2,
+        vy=-1.1,
+        vz=0.05,
+    )
+    payload = encode_state("dr-01", pose, flags=0)
+    assert len(payload) == FRAME.size
+
+    decoded = decode_state(payload)
+    assert decoded is not None
+    assert decoded["peer_id"] == "dr-01"
+    assert decoded["ts_ns"] == pose.ts_ns
+    assert decoded["pos_x"] == pytest.approx(pose.x, abs=0.001)
+    assert decoded["pos_y"] == pytest.approx(pose.y, abs=0.001)
+    assert decoded["pos_z"] == pytest.approx(pose.z, abs=0.001)
+    assert decoded["roll"] == pytest.approx(pose.roll, abs=0.01)
+    assert decoded["pitch"] == pytest.approx(pose.pitch, abs=0.01)
+    assert decoded["yaw"] == pytest.approx(pose.yaw, abs=0.01)
+
+
+def test_rejects_invalid_payload() -> None:
+    assert decode_state(b"short") is None
+    assert decode_state(b"XX" + b"\0" * (FRAME.size - 2)) is None