feat(v1): relax fall sensitivity for low overhead cameras

Adds configurable event.require_rapid_drop (default off), require_lower_body
(default off) and horizontal_angle_threshold_degrees (default 45). With the
lenient defaults a sustained horizontal pose alone enters SUSPECT and confirms
after the confirm window, which is now the main false-positive guard; missing
knees/ankles no longer reject the pose. Thresholds flow into config_version.
End-to-end smoke confirms a lying pose; 70 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v1/tests/test_config.py

@@ -140,6 +140,20 @@ def test_public_example_config_has_no_embedded_credentials():
     assert "rtsp_url_env" in source
 
 
+def test_sensitivity_fields_default_to_lenient(tmp_path):
+    config_file = tmp_path / "config.json"
+    _write_config(
+        config_file,
+        {"id": "c", "host": "192.0.2.10", "username": "u", "password": "p"},
+    )
+
+    config = load_config(config_file)
+
+    assert config.event.require_rapid_drop is False
+    assert config.event.require_lower_body is False
+    assert config.event.horizontal_angle_threshold_degrees == 45.0
+
+
 def test_build_ffmpeg_options_variants():
     assert build_ffmpeg_options() == "rtsp_transport;tcp|stimeout;5000000|fflags;nobuffer|flags;low_delay"
     assert build_ffmpeg_options("udp", 3, False) == "rtsp_transport;udp|stimeout;3000000"

v1/tests/test_evidence.py

@@ -36,6 +36,14 @@ def test_missing_ankles_rejects_pose():
     assert quality.reason == "required_joint_low_confidence"
 
 
+def test_missing_ankles_accepted_when_lower_body_not_required():
+    quality = assess_pose_quality(
+        _pose(missing_ankles=True), threshold=0.4, require_lower_body=False
+    )
+
+    assert quality.accepted is True
+
+
 def test_horizontal_body_is_evidence_not_event():
     pose = _pose(horizontal=True)
     quality = assess_pose_quality(pose, threshold=0.4)

v1/tests/test_fall_policy.py

@@ -42,6 +42,20 @@ def test_rejected_pose_clears_pending_drop_before_the_next_horizontal_pose():
     assert candidate.is_fall_candidate is False
 
 
+def test_horizontal_pose_alone_starts_candidate_when_rapid_drop_not_required():
+    policy = FallEvidencePolicy(suspect_window_seconds=0.5, require_rapid_drop=False)
+
+    candidate = policy.evaluate(
+        "P-0001", _evidence(horizontal=True), now=0.0, state=FallState.NORMAL
+    )
+    upright = policy.evaluate(
+        "P-0002", _evidence(horizontal=False), now=0.0, state=FallState.NORMAL
+    )
+
+    assert candidate.is_fall_candidate is True
+    assert upright.is_fall_candidate is False
+
+
 def test_upright_pose_is_recovery_evidence_only_after_confirmation():
     policy = FallEvidencePolicy(suspect_window_seconds=0.5)