Tighten recognition: raise threshold to 0.50, add 2-hit debounce

Two fixes for "always recognises the same person":

1. Threshold 0.35 → 0.50
MobileFaceNet embeddings for different people typically score 0.20–0.45;
the same person scores 0.55–0.85. The old threshold of 0.35 sits right
in the overlap zone, so random faces exceeded it. 0.50 sits safely
above the inter-person range while remaining reachable for the same
person.

2. 2-hit recognition debounce (RECOGNITION_DEBOUNCE = 2)
The same name must appear in two consecutive 0.5-second frames before
GREETING is triggered. A single ambiguous frame (slight pose change,
partial occlusion) can no longer cause a false positive. The counter
resets on every mismatch, NoFaceDetected, wake-up, or state change.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

recognizer/face_db.py

@@ -214,7 +214,7 @@ def wipe() -> None:
 def find_match(
     frame_bgr: np.ndarray,
     db: dict[str, list[list[float]]],
-    threshold: float = 0.35,
+    threshold: float = 0.50,
 ) -> Optional[str]:
     """Return matched name if recognised, None if face present but unknown.
 

recognizer/main.py

@@ -23,10 +23,11 @@ from recognizer.tts import speak
 
 logger = logging.getLogger(__name__)
 
-ACTIVE_TIMEOUT = 15.0     # seconds before returning to sleep with no face
-DOA_DEBOUNCE   = 3        # consecutive speech-detected readings to wake up
-FACE_INTERVAL  = 0.5      # seconds between face-recognition attempts
-SCAN_AMPLITUDE = 0.35     # head scan amplitude (world-y, metres) during ACTIVE
+ACTIVE_TIMEOUT      = 15.0  # seconds before returning to sleep with no face
+DOA_DEBOUNCE        = 3     # consecutive speech-detected readings to wake up
+FACE_INTERVAL       = 0.5   # seconds between face-recognition attempts
+SCAN_AMPLITUDE      = 0.35  # head scan amplitude (world-y, metres) during ACTIVE
+RECOGNITION_DEBOUNCE = 2    # consecutive same-name hits required to confirm identity
 
 
 class State(Enum):
@@ -93,7 +94,9 @@ class Recognizer(ReachyMiniApp):
         last_face_check = 0.0
         enrollment_frames: list[np.ndarray] = []
         greeting_name = ""
-        scan_t0 = 0.0             # reference time for head-scan idle animation
+        rec_candidate = ""   # name accumulating consecutive hits
+        rec_hits = 0         # consecutive hit count for rec_candidate
+        scan_t0 = 0.0        # reference time for head-scan idle animation
 
         reachy_mini.goto_sleep()
 
@@ -134,6 +137,8 @@ class Recognizer(ReachyMiniApp):
                 scan_t0 = active_start
                 last_face_check = 0.0
                 enrollment_frames.clear()
+                rec_candidate = ""
+                rec_hits = 0
                 state = State.ACTIVE
 
             # ---------- ACTIVE ----------
@@ -157,12 +162,27 @@ class Recognizer(ReachyMiniApp):
                             name = find_match(frame, face_db)
                             jpeg = get_face_jpeg(frame)
                             if name:
-                                greeting_name = name
-                                with _lock:
-                                    _shared["recognized_name"] = name
-                                    _shared["snapshot"] = jpeg
-                                state = State.GREETING
+                                # Debounce: require RECOGNITION_DEBOUNCE consecutive
+                                # hits of the same name before confirming.
+                                if name == rec_candidate:
+                                    rec_hits += 1
+                                else:
+                                    rec_candidate = name
+                                    rec_hits = 1
+                                logger.debug("Recognition hit %d/%d: %s",
+                                             rec_hits, RECOGNITION_DEBOUNCE, name)
+                                if rec_hits >= RECOGNITION_DEBOUNCE:
+                                    rec_candidate = ""
+                                    rec_hits = 0
+                                    greeting_name = name
+                                    with _lock:
+                                        _shared["recognized_name"] = name
+                                        _shared["snapshot"] = jpeg
+                                    state = State.GREETING
                             else:
+                                # Unknown face — reset debounce and enroll
+                                rec_candidate = ""
+                                rec_hits = 0
                                 speak(
                                     "I don't know you yet. "
                                     "Please enter your name on the control panel.",
@@ -174,7 +194,8 @@ class Recognizer(ReachyMiniApp):
                                     _shared["snapshot"] = jpeg
                                 state = State.ENROLLING
                         except NoFaceDetected:
-                            pass  # no face in frame yet, keep scanning
+                            rec_candidate = ""
+                            rec_hits = 0
 
                 # Timeout: nobody showed up
                 if state == State.ACTIVE and time.time() - active_start > ACTIVE_TIMEOUT: