fix(v1): use ASCII screenshot annotation to avoid garbled text

cv2.putText only supports ASCII (Hershey fonts); the middle-dot in the
label rendered as garbage on saved screenshots. screenshot_label builds
an ASCII-only 'ID STATE' string for the annotation; the Qt live-view
label is unchanged. 72 tests pass.

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

v1/alerts.py

@@ -46,6 +46,18 @@ class AlertSink:
         pass
 
 
+def screenshot_label(track_id: str, state_value: str) -> str:
+    """ASCII-only label for ``cv2.putText``.
+
+    OpenCV's Hershey fonts render only ASCII; non-ASCII characters (such as the
+    middle dot used in the live-view label) come out garbled, so the screenshot
+    label is built from the id and state and stripped to ASCII.
+    """
+
+    text = "{0} {1}".format(track_id, state_value)
+    return text.encode("ascii", "ignore").decode("ascii")
+
+
 def annotate_frame(image: np.ndarray, view: MonitorViewState) -> np.ndarray:
     """Return a copy of ``image`` with boxes, skeleton, labels and a state border."""
 
@@ -67,7 +79,7 @@ def annotate_frame(image: np.ndarray, view: MonitorViewState) -> np.ndarray:
                 cv2.circle(canvas, (int(round(point.x)), int(round(point.y))), 3, color, -1)
         cv2.putText(
             canvas,
-            overlay.label,
+            screenshot_label(overlay.track_id, overlay.state.value),
             (left, max(0, top - 6)),
             cv2.FONT_HERSHEY_SIMPLEX,
             0.5,

v1/tests/test_alerts.py

@@ -4,7 +4,13 @@ from datetime import datetime, timezone
 import numpy as np
 import pytest
 
-from v1.alerts import AlertDispatcher, AlertSink, EventArtifactWriter, annotate_frame
+from v1.alerts import (
+    AlertDispatcher,
+    AlertSink,
+    EventArtifactWriter,
+    annotate_frame,
+    screenshot_label,
+)
 from v1.fall_state import FallEvent, FallState
 from v1.view_model import MonitorViewState, PersonOverlay, Point, StatusColor
 
@@ -115,6 +121,20 @@ def test_distinct_events_produce_two_log_lines(tmp_path):
     assert len(lines) == 2
 
 
+def test_screenshot_label_is_ascii_only():
+    label = screenshot_label("P-0001", "CONFIRMED")
+
+    assert label == "P-0001 CONFIRMED"
+    assert all(ord(ch) < 128 for ch in label)
+
+
+def test_screenshot_label_strips_non_ascii_separator():
+    # The live-view label uses a middle dot; the screenshot label must not.
+    label = screenshot_label("P-0001", "CONFIRMED")
+
+    assert "·" not in label
+
+
 def test_annotate_draws_red_border_only_for_confirmed():
     image = np.full((60, 80, 3), 30, dtype=np.uint8)
     confirmed = annotate_frame(image, _confirmed_view())