Fix wake beacon serial latency and pretty-print JSON

src/switch_pico_bridge/wake_beacon.py

@@ -224,13 +224,20 @@ class WakeBeaconClient:
 
     def _exchange(self, command: bytes, deadline: float) -> WakeBeaconStatus:
         try:
-            self.transport.write_timeout = min(0.25, self._remaining(deadline))
+            write_timeout = min(0.25, self._remaining(deadline))
+            if self.transport.write_timeout != write_timeout:
+                self.transport.write_timeout = write_timeout
             # A partial write may already have reached the device. Never resend.
             if self.transport.write(command) != len(command):
                 raise TransportError("Incomplete serial write; command was not retried")
             response = bytearray()
             while True:
-                self.transport.timeout = min(0.1, self._remaining(deadline))
+                read_timeout = min(0.1, self._remaining(deadline))
+                # pyserial reconfigures the Windows port on every assignment,
+                # even for an unchanged timeout. Avoid USB control transfers
+                # per response byte, while still shortening reads at deadline.
+                if self.transport.timeout != read_timeout:
+                    self.transport.timeout = read_timeout
                 chunk = self.transport.read(1)
                 if not chunk:
                     continue
@@ -398,7 +405,7 @@ def main(argv: Sequence[str] | None = None) -> int:
             "status": exc.status.to_dict() if exc.status else None,
         }
         if args.json:
-            print(json.dumps(result, separators=(",", ":")))
+            print(json.dumps(result, indent=2))
         else:
             print(f"Wake beacon: {exc}", file=sys.stderr)
         return 1
@@ -406,11 +413,11 @@ def main(argv: Sequence[str] | None = None) -> int:
         print(
             json.dumps(
                 {"ok": True, "action": action, "status": status.to_dict()},
-                separators=(",", ":"),
+                indent=2,
             )
         )
     elif args.status:
-        print(json.dumps(status.to_dict(), sort_keys=True))
+        print(json.dumps(status.to_dict(), indent=2, sort_keys=True))
     else:
         print(
             f"Advertising burst complete (request {status.request_id}); console power state is not confirmed."

tests/test_wake_beacon.py

@@ -179,6 +179,28 @@ def test_fragmented_burst_completes_once_and_excludes_retained_id(beacon):
     assert beacon.closed
 
 
+def test_slow_serial_reconfiguration_does_not_delay_each_response_byte(
+    beacon, monkeypatch
+):
+    # pyserial reconfigures an open Windows port even when assigned the same
+    # timeout. Model USB control-transfer latency on each such assignment.
+    def set_timeout(device, value):
+        device.__dict__["timeout"] = value
+        device.clock.sleep(0.02)
+
+    monkeypatch.setattr(
+        SimulatedBeacon,
+        "timeout",
+        property(lambda device: device.__dict__["timeout"], set_timeout),
+        raising=False,
+    )
+    result = wake.request_wake("COM13", timeout=1)
+    assert result.state == "complete"
+    assert beacon.bursts == 1
+    assert beacon.clock.now < 1
+    assert beacon.closed
+
+
 @pytest.mark.parametrize(
     "change",
     [