Adversarial-review fixes for the #93057 snapshot-compaction PR:
- Fail-closed detachment: only re-enable compression after
bind_session_state successfully severs the engine's parent binding.
A failed rebind keeps the historical compression_enabled=False
behavior and warns, instead of running compaction against a
compressor still bound to the parent's SessionDB (#38727 re-open).
- Warm-cache parity: defer both compression gates (turn-prologue
preflight + pre-API pressure check) until the fork's first provider
response, so the first request replays the full snapshot as the
intended cached read and compaction applies from the second request
on — matching the documented budget mental model.
- Tests: regression for the rebind-failure fail-closed path (red on
pre-fix code) and the existing threshold-crossing test reworked to a
two-request review asserting the warm first request + compacted
second request. 116 tests green across all touched suites; ruff
clean.
Finn763
74e6885f0d