Add src/build_cache_pruner.py — a background daemon thread modelled 1:1 on
src/disk_watchdog.py that periodically runs STRICTLY `docker builder prune -f
--filter until=<until>` (BuildKit GC) on the HOST over ssh. It is the "second
half" of the disk-watchdog (ORCH-063): the watchdog signals, the pruner cleans.
Removes the root cause of the 07.06.2026 incident (build cache ~11GB -> disk
100% -> whole self-hosting pipeline down) automatically, без оператора.
ADR-001 (Variant A): host-over-ssh, same channel as image_freshness/self_deploy
(no docker CLI in the image). Touches ONLY the build cache — no image/system
prune, no image/container removal, never restarts the docker daemon or the prod
container (self-hosting safety). No ssh target -> tick is a no-op.
- src/config.py: ORCH_BUILD_CACHE_PRUNE_* flags + defensive validators
(interval/timeout >0, until ~ ^\d+[smhdw]?$, notify_min_gb >=0 -> safe default).
- src/main.py: start last (after disk_watchdog) / stop first in lifespan;
additive read-only build_cache_prune block in GET /queue.
- never-raise on two levels (per-command + per-tick); kill-switch
ORCH_BUILD_CACHE_PRUNE_ENABLED (false -> daemon does not start, 1:1 as before).
- STAGE_TRANSITIONS / QG_CHECKS / check_* / _parse_* / DB schema UNCHANGED;
last-run/last-result is in-memory (no migration).
- tests/test_build_cache_pruner.py: TC-01..TC-12 (23 cases, docker fully mocked).
- .env.example + CHANGELOG.md updated; INFRA.md / architecture docs already
carry the component (architecture stage).
Refs: ORCH-062
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
