/compact + opt-in [compaction] auto gate work in every trustee session
surface (CLI/web/xagent) with ZERO trustee-side code changes: abk 0.21
intercepts /compact after checkpoint restore inside execute_run, and the
auto gate runs pre-request in the orchestration loop off the same config
TOML. DEFAULT OFF — no behavior change until an explicit /compact or a
config flip (deploy lane).

ROOT CAUSE (the gap): no compaction anywhere in the stack; abk's only
history control was the lossy execution.max_history=20 silent drop.

GATES: 175/175 x3 (THQ_IT_PDT_BIN real-PDT suite, matches 0.21.3
baseline); release build links abk-0.21.0 (strings-verified; lock
pre-flight cargo update -p abk applied); release warnings 2 (pre-existing
cursor/did_something — no .rs files in this diff, delta 0).

PINS: abk 0.20 -> 0.21 (root/api/core/tui); versions core 0.8.7,
tui 0.4.8, api 0.19.17, root 0.22.0. PUBLISH: dep-order core -> tui ->
api -> root (dry-run per crate before upload). DUAL-REMOTE: origin-only
clone; forgejo mirror-sync is on the deploy lane. dead-tag: none.