Host toolchain resource

automobile:host/toolchain is a read-only diagnostic MCP resource. It reports host-tool availability for adb, emulator, sdkmanager, avdmanager, xcodebuild, xcode-select, xcrun, simctl, and devicectl.

Its JSON content has a lastUpdated ISO-8601 timestamp and an entries array. Each entry has a canonical name and available boolean. version and location are included when known; an unavailable entry includes error when there is a specific probe failure.

location is reported only when the probe returned an absolute path (POSIX or Windows drive-letter); a bare command name such as adb is omitted.

Every probe races the doctor check against DOCTOR_EXEC_TIMEOUT_MS. When the deadline wins, the entry reports the timeout and the resource aborts the losing check through the DoctorProbeOptions signal, so the commands it spawned (for example emulator -list-avds or an adb path probe) are killed rather than accumulating across repeated reads (#7008).

version and location are advisory information and must not gate automation. available for adb, and for at least one Apple developer-tooling entry, is an operational requirement for the corresponding AutoMobile device automation. This resource itself is diagnostic only: it does not gate any tool call, change host state. Its CoreDevice diagnostic reads existing simulator state. Doctor and readiness gating remain separate and are unaffected.

The devicectl entry’s coreDevice payload reports simulatorBootState as { status: "available", booted, shutdown, unknown }, or unavailable with a reason. Counts include transitional states as unknown and have fixed payload size. A one-second cached/coalesced simctl listing bounds repeat reads; fresh boot checks bypass this diagnostic cache and simctl’s stale fallback.

capabilities contains status (not probed or probed) and at most 64 entries, each with simulator-type scope, command, status (supported or unsupported), and featureId when captured. Success captures do not contain a feature ID, so supported commands retain their command name. An unobserved command is not probed. Unsupported feature IDs and learned command links each use a 64-entry FIFO bound. Type/runtime scope prevents a non-Duo hinge failure disabling a Duo; unknown types fall back to the device ID.

Reading this resource or running the CoreDevice doctor check performs the existing bounded devicectl --version availability read every time. The measured result seeds the injected process-owned probe, so a later checkSimulatorCommand reuses it without a second version invocation. Concurrent version reads share an in-flight invocation. Capability commands stay lazy: diagnostic reads never spawn them. There is currently no production simulator command caller; the existing simulator tools use simctl. No new tool is introduced.

The downgrade guard is out of scope per the owner decision on 2026-10-02 and is not reported.