Add Edge TPU subprocess probe to safely detect segfaults

Probes the Edge TPU in a subprocess before loading — catches segfaults
(libedgetpu ABI mismatch on Debian Trixie/Python 3.13) and falls back
to CPU automatically. No more service crashes on Coral incompatibility.

When the runtime is eventually fixed, Edge TPU will be used automatically
with no config changes needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sound_id.py

@@ -85,6 +85,29 @@ CATEGORY_GROUPS = {
 
 
 class SoundClassifier:
+    @staticmethod
+    def _probe_edgetpu(model_path: str) -> bool:
+        """Test Edge TPU in a subprocess to catch segfaults safely."""
+        import subprocess, sys
+        try:
+            result = subprocess.run(
+                [sys.executable, "-c",
+                 "import ai_edge_litert.interpreter as tfl; "
+                 f"d = tfl.load_delegate('libedgetpu.so.1'); "
+                 f"i = tfl.Interpreter(model_path='{model_path}', experimental_delegates=[d]); "
+                 "i.allocate_tensors(); "
+                 "print('ok')"],
+                capture_output=True, text=True, timeout=10
+            )
+            if result.returncode == 0 and "ok" in result.stdout:
+                logger.info("Edge TPU probe: OK")
+                return True
+            logger.warning("Edge TPU probe failed: %s", result.stderr.strip() or f"exit {result.returncode}")
+            return False
+        except Exception as e:
+            logger.warning("Edge TPU probe error: %s", e)
+            return False
+
     def __init__(self, model_path, class_map_path, use_edgetpu=False):
         # Load class names
         self._class_names = []
@@ -105,14 +128,21 @@ class SoundClassifier:
         import ai_edge_litert.interpreter as tfl
 
         if use_edgetpu:
-            delegate = tfl.load_delegate("libedgetpu.so.1")
-            self._interp = tfl.Interpreter(
-                model_path=str(model_path),
-                experimental_delegates=[delegate],
-            )
-            logger.info("YAMNet loaded on Edge TPU")
-        else:
-            self._interp = tfl.Interpreter(model_path=str(model_path))
+            if self._probe_edgetpu(model_path):
+                delegate = tfl.load_delegate("libedgetpu.so.1")
+                self._interp = tfl.Interpreter(
+                    model_path=str(model_path),
+                    experimental_delegates=[delegate],
+                )
+                logger.info("YAMNet loaded on Edge TPU")
+            else:
+                logger.warning("Edge TPU probe failed (segfault or error) — falling back to CPU")
+                use_edgetpu = False
+
+        if not use_edgetpu:
+            # Use CPU model (swap edgetpu model path for CPU model if needed)
+            cpu_path = str(model_path).replace("_edgetpu.tflite", ".tflite")
+            self._interp = tfl.Interpreter(model_path=cpu_path)
             logger.info("YAMNet loaded on CPU")
 
         self._interp.allocate_tensors()