Accept USB BOOTSEL reboot on the UART firmware

The regular firmware now answers the EP0 vendor INFO and BOOTSEL reboot
requests with the AIO wire protocol, so switch-pico-config reboot bootsel
works when the Pico's USB side is on a PC. Wire constants move to
usb_management_protocol.h; other operations stall.

tests/test_uart_usb_management_native.py

@@ -0,0 +1,78 @@
+"""The UART firmware's EP0 management must interoperate with config_manager."""
+
+from __future__ import annotations
+
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+from switch_pico_bridge import config_manager
+
+
+@pytest.fixture(scope="module")
+def harness(tmp_path_factory: pytest.TempPathFactory) -> Path:
+    root = Path(__file__).resolve().parents[1]
+    compiler = shutil.which("c++") or shutil.which("g++")
+    assert compiler is not None, "a host C++ compiler is required"
+    executable = tmp_path_factory.mktemp("uart_usb_management") / "harness"
+    subprocess.run(
+        [
+            compiler,
+            "-std=c++17",
+            "-Wall",
+            "-Wextra",
+            "-Werror",
+            "-pedantic",
+            "-DSWITCH_PICO_HID_INSTANCE_COUNT=4",
+            f"-I{root / 'tests' / 'native_stubs'}",
+            f"-I{root / 'src' / 'firmware'}",
+            str(root / "src" / "firmware" / "usb" / "uart_usb_management.cpp"),
+            str(root / "src" / "firmware" / "configuration" / "configuration_storage.cpp"),
+            str(root / "tests" / "uart_usb_management_test.cpp"),
+            "-o",
+            str(executable),
+        ],
+        check=True,
+        cwd=root,
+    )
+    return executable
+
+
+def run(harness: Path, *args: str) -> str:
+    return subprocess.run(
+        [str(harness), *args], check=True, capture_output=True, text=True
+    ).stdout.strip()
+
+
+def test_info_response_parses_as_a_regular_pico(harness: Path) -> None:
+    response = bytes.fromhex(run(harness, "info"))
+    envelope = config_manager.parse_response(response, config_manager.OP_INFO)
+    assert envelope.status == config_manager.STATUS_OK
+    version = tuple(envelope.payload[:3])
+    board, active_mode, capabilities = envelope.payload[3:6]
+    assert version == (0, 2, 0)
+    assert config_manager.BOARD_NAMES[board] == "Pico"
+    assert config_manager.ACTIVE_MODE_NAMES[active_mode] == "Switch"
+    assert capabilities & config_manager.CAPABILITY_INPUT
+    assert capabilities & ~config_manager.CAPABILITY_MASK == 0
+
+
+def test_bootsel_request_from_config_manager_reboots_after_status_stage(
+    harness: Path,
+) -> None:
+    request = config_manager.encode_request(config_manager.OP_BOOTSEL_REBOOT, b"")
+    assert run(harness, "bootsel", request.hex()) == "accepted=1 early=0 reboot=1"
+
+
+def test_corrupted_bootsel_request_is_rejected_without_rebooting(harness: Path) -> None:
+    request = bytearray(config_manager.encode_request(config_manager.OP_BOOTSEL_REBOOT, b""))
+    request[-1] ^= 0x01  # break the payload CRC
+    assert run(harness, "bootsel", bytes(request).hex()) == "accepted=0 early=0 reboot=0"
+    wrong_operation = config_manager.encode_request(config_manager.OP_REBOOT, b"")
+    assert run(harness, "bootsel", wrong_operation.hex()) == "accepted=0 early=0 reboot=0"
+
+
+def test_unsupported_operations_are_stalled(harness: Path) -> None:
+    assert run(harness, "other", str(config_manager.OP_CONFIGURATION_READ)) == "accepted=0"