The concurrent-compression regression asserted the parent ends with exactly
one child. Under heavy CI write contention the lock winner's child
create_session can exhaust its SQLite retry budget, and _compress_context
deliberately rolls the live id back to the still-indexed parent rather than
orphaning a child (the create-failure rollback in
agent/conversation_compression.py). That safe rollback leaves zero children
and is correct — so the exact == 1 assertion flaked under load.
Assert the actual invariant instead: children <= 1 (a 2+ fork is the bug
Damien's incident is about), rotated <= 1, and rotated == n_children. A
mutation check (force the lock to always acquire) confirms the relaxed
assertion still fails hard on a real 2-child fork.
Teknium
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