Cuts detect's wall time substantially by sharing fork-exec results
between the helper that walks the JSON output and the localEngineStatus
classifier from lib/gbrain-local-status.ts.
Before: detect made 2x `command -v gbrain` calls (one in detect's
detectGbrain, one in the classifier's resolveGbrainBin) and 2x
`gbrain --version` calls. With memoization keyed on PATH, both
collapse to one fork each (~400ms saved per skill preamble).
Also adds `--fast` to the `gbrain doctor --json` call in detect so a
broken-db config (Garry's repro) doesn't burn a full 5s timeout on the
doctor's DB-connection check. The classifier still probes the DB
directly via `gbrain sources list --json` for engine reachability —
that's `gbrain_local_status`, separate from the coarse
`gbrain_doctor_ok` summary flag.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
