Live Debugging MCP

Live DAT Debugging with MCP (iOS)

Use this skill when a developer is debugging an iOS DAT app and has a local DAT Inspector MCP server or DAT debug server available to the agent. This is the live-runtime counterpart to dat-docs-mcp: use docs search for API lookup, and use this skill for observed app/device behavior.

Ground rules

• Stay read-only unless the user explicitly asks for an app code change.
• Do not mutate Meta AI app, device, account, permission, registration, or app state.
• Treat companion-app/device results as boundary diagnosis from app-visible DAT events, not as direct access to companion app internals.
• Use live DAT evidence before guessing: registration, permissions, device selection, link state, session state, stream state, typed errors, and SDK logs.
• If the MCP tools are not configured, ask the developer to enable their local DAT debug setup and fall back to logs plus search_dat_docs.

Normal agent loop

1. Discover and connect to the running app debug server:
   • discover_debug_servers
   • connect_to_debug_server
2. Establish the baseline with all three calls before diagnosing deeper:
   • get_connection_status
   • get_sdk_state
   • get_dat_readiness Do not skip get_connection_status; it separates MCP/debug-server connectivity from SDK, registration, permission, session, and stream state.
3. If the issue looks like Meta AI app or device boundary behavior, inspect:
   • get_companion_boundary_diagnosis
   • get_device_path
   • get_permissions
   • get_device_properties
4. Ask the developer to reproduce the failing iOS flow while connected.
5. Wait for narrow evidence instead of polling everything:
   • wait_for_events with category or source
   • get_errors
   • get_event_digest
6. For handoff, collect a redacted bundle:
   • export_diagnostic_bundle

Evidence map

• Configuration: app logs around Wearables.configure()
• URL callbacks: Wearables.shared.handleUrl(_:) return handling
• Registration: Wearables.shared.startRegistration() and wearables.registrationState
• Device availability: device selectors, wearables.devices, device.compatibility, and device.properties
• Device link: device.linkState
• Permissions: DAT permission APIs, device.permission, check_permissions, and get_permissions
• Session: DeviceSession creation/start, deviceSession.state, session.state, and session errors
• Stream: stream start, stream.state, frame counters, and stream errors
• DAM/DWA-visible transport: sdk.usesDam and DAM/DWA error values

Diagnosis patterns

• Registration blocked: verify Info.plist DAT configuration, app URL scheme, Developer Mode setup, and callback handling.
• No eligible device: inspect discovered devices, selector behavior, device compatibility, and device.linkState before changing stream code.
• Permission failure: use get_permissions and get_companion_boundary_diagnosis; do not assume iOS system permission is the same as DAT permission through the Meta AI app/device boundary.
• Session fails before stream creation: inspect session errors and selected device compatibility before changing camera code.
• Stream fails after session start: inspect stream state, camera permission, and recent errors before changing frame processing.

Output expectations

When summarizing, name the evidence plane, the blocking state, and the next developer action. Example:

DAT readiness is blocked at registration: the app-visible registration state is
not registered. Check the Info.plist DAT URL scheme and MetaAppID, complete the
Meta AI callback through handleUrl(_:), then retry while the MCP connection waits
for registration and device-link events.