Handle cold-boot timeout for TCP connections

- bridges/tcp_serial_bridge.py: increase default boot_delay 2s → 8s to
  cover MiniMate Plus cold-start time (unit wakes from RS-232 line
  assertion but takes 5-10s to be ready for POLL_PROBE).
- sfm/server.py: add _run_with_retry() — on TCP connections only, retries
  once on ProtocolError. Serial timeouts are not retried (usually a real
  fault). Confirmed behaviour: unit wakes purely from RS-232 line voltage,
  no software wake-up frame needed.

bridges/tcp_serial_bridge.py

@@ -55,8 +55,10 @@ DEFAULT_TCP_PORT = 12345
 CHUNK            = 256          # bytes per read call
 SERIAL_TIMEOUT   = 0.02         # serial read timeout (s) — non-blocking in practice
 TCP_TIMEOUT      = 0.02         # socket recv timeout (s)
-BOOT_DELAY       = 2.0          # seconds to wait after opening serial port before
+BOOT_DELAY       = 8.0          # seconds to wait after opening serial port before
-                                # forwarding data — mirrors the unit's startup beep
+                                # forwarding data — unit cold-boot (beep + OS init)
+                                # takes 5-10s from first RS-232 line assertion.
+                                # Set to 0 if unit was already running before connect.
 
 
 # ── Bridge session ─────────────────────────────────────────────────────────────

sfm/server.py

@@ -170,6 +170,31 @@ def _build_client(
         )
 
 
+def _is_tcp(host: Optional[str]) -> bool:
+    return bool(host)
+
+
+def _run_with_retry(fn, *, is_tcp: bool):
+    """
+    Call fn() and, for TCP connections only, retry once on ProtocolError.
+
+    Rationale: when a MiniMate Plus is cold (just had its serial lines asserted
+    by the modem or a local bridge), it takes 5-10 seconds to boot before it
+    will respond to POLL_PROBE.  The first request may time out during that boot
+    window; a single automatic retry is enough to recover once the unit is up.
+
+    Serial connections are NOT retried — a timeout there usually means a real
+    problem (wrong port, wrong baud, cable unplugged).
+    """
+    try:
+        return fn()
+    except ProtocolError as exc:
+        if not is_tcp:
+            raise
+        log.info("TCP poll timed out (unit may have been cold) — retrying once")
+        return fn()   # let any second failure propagate normally
+
+
 # ── Endpoints ──────────────────────────────────────────────────────────────────
 
 @app.get("/health")
@@ -195,8 +220,10 @@ def device_info(
     log.info("GET /device/info  port=%s host=%s tcp_port=%d", port, host, tcp_port)
 
     try:
-        with _build_client(port, baud, host, tcp_port) as client:
+        def _do():
-            info = client.connect()
+            with _build_client(port, baud, host, tcp_port) as client:
+                return client.connect()
+        info = _run_with_retry(_do, is_tcp=_is_tcp(host))
     except HTTPException:
         raise
     except ProtocolError as exc:
@@ -242,9 +269,10 @@ def device_events(
     log.info("GET /device/events  port=%s host=%s", port, host)
 
     try:
-        with _build_client(port, baud, host, tcp_port) as client:
+        def _do():
-            info   = client.connect()
+            with _build_client(port, baud, host, tcp_port) as client:
-            events = client.get_events()
+                return client.connect(), client.get_events()
+        info, events = _run_with_retry(_do, is_tcp=_is_tcp(host))
     except HTTPException:
         raise
     except ProtocolError as exc:
@@ -278,9 +306,11 @@ def device_event(
     log.info("GET /device/event/%d  port=%s host=%s", index, port, host)
 
     try:
-        with _build_client(port, baud, host, tcp_port) as client:
+        def _do():
-            client.connect()
+            with _build_client(port, baud, host, tcp_port) as client:
-            events = client.get_events()
+                client.connect()
+                return client.get_events()
+        events = _run_with_retry(_do, is_tcp=_is_tcp(host))
     except HTTPException:
         raise
     except ProtocolError as exc: