New session now refuses to spawn a Pi runtime that would only die in bootstrap
retrieval when the DWH/vector host is unreachable (e.g. a dropped VPN). Before
`session new`, POST /sessions probes the DWH via `tht db ping`; if it is down it
returns 503 {code:"dwh_unreachable"} with a clear message and creates nothing.
- Gated behind the THT_DWH_PRECHECK flag (default off), enabled only by the local
dev launcher (run-stack.sh) — containers/CI never pay the probe, and existing
tests that don't set it are unaffected.
- ThtRunner.dbPing() runs `tht db ping` with a 10s timeout (run() gains an optional
timeout that SIGKILLs a hung child).
- Frontend: apiFetch throws a typed ApiError (status + parsed payload); the new-
session composer shows the specific alert on `dwh_unreachable` instead of the
generic retry hint, keeping the question for retry.
Verified live on an isolated backend (precheck on + broken DWH host → 503
dwh_unreachable, no session created) and via unit tests (backend 228, frontend 308).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
marcopan
