fix(worker): return structured internal endpoint errors

app/worker/internal_server.py

@@ -14,11 +14,36 @@ class WorkerHTTPRequestHandler(BaseHTTPRequestHandler):
     """
     Lightweight HTTP request handler for worker internal metrics and stats.
     """
+    error_content_type = "application/json"
 
     def log_message(self, format: str, *args) -> None:
         # Suppress default noisy stderr logging
         pass
 
+    def send_error(self, code: int, message: Optional[str] = None, explain: Optional[str] = None) -> None:
+        from http import HTTPStatus
+        try:
+            if hasattr(self, "headers") and self.headers:
+                content_length = int(self.headers.get("Content-Length", 0))
+                if content_length > 0:
+                    self.rfile.read(min(content_length, 65536))
+        except Exception:
+            pass
+        try:
+            status = HTTPStatus(code)
+            short_msg = status.phrase
+        except ValueError:
+            short_msg = "error"
+        err_msg = message or short_msg
+        detail = explain or err_msg
+        body = json.dumps({"error": err_msg, "detail": detail}).encode("utf-8")
+        self.send_response(code)
+        self.send_header("Content-Type", "application/json")
+        self.send_header("Content-Length", str(len(body)))
+        self.send_header("Connection", "close")
+        self.end_headers()
+        self.wfile.write(body)
+
     def do_GET(self) -> None:
         if self.path == "/internal/stats":
             stats = worker_metrics.get_internal_stats()
@@ -51,12 +76,7 @@ class WorkerHTTPRequestHandler(BaseHTTPRequestHandler):
             self.wfile.write(body)
             return
 
-        self.send_response(404)
-        self.send_header("Content-Type", "application/json")
-        body = b'{"error": "not_found"}'
-        self.send_header("Content-Length", str(len(body)))
-        self.end_headers()
-        self.wfile.write(body)
+        self.send_error(404, "not_found", f"Cannot GET {self.path}")
 
 
 class WorkerInternalServer: