P1 (cubic-dev-ai): Test process PID differs from spawned hook PID,
so test was seeding/clearing wrong state file. Fix: pass fixed
CLAUDE_SESSION_ID='gateguard-test-session' to spawned hooks.
P2 (cubic-dev-ai): Pruning checked array could evict __bash_session__
and other session keys, causing gates to re-fire mid-session. Fix:
preserve __prefixed keys during pruning, only evict file-path entries.
9/9 tests pass.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>