fixed retained-kernel restart and owner cleanup edge cases during recovery and disposal
tracked async user_python hooks during disposal-sensitive execution paths and hardened startup warmup tracking
strengthened cleanup and kernel lifecycle regressions to remove deadlocks, false positives, and timing flakes
scoped retained-kernel ownership to agent sessions and cleaned it up on session disposal
cleaned up warmed python owners on session startup failure and rejected new direct and tool-based python starts during disposal, including async hook, preflight, and warmup races
Carl