yield-injections

Append a variant to the appropriate YieldPoint enum without reordering existing variants, place the inject_transition_yield! macro after the transition that makes resume safe, and add a deterministic test with FixedYieldInjector. Reordering changes ordinals and breaks simulator seed reproducibility.

Use FixedFailureInjector mapped to a CommitYieldPoint such as AfterRemoveTx, then verify transaction maps, connection slots, locks, and exclusive transaction atomics are not stranded. Failure injection only works for TransitionResult state machines; there is no inject_io_failure! macro.

The ordinal is computed as self as u8 from source order, and simulator plans store raw ordinals rather than names. Reordering silently retargets existing seeds to different hooks, making CI seeds, bisects, and simulator coverage non-reproducible.

No, the concurrent simulator owns randomized deterministic injection through SimulatorYieldInjector keyed by instance_id, selection_key, and point_count. Fixed injectors are intended only for targeted unit tests on a connection.

Re-entry must be safe: mutate the state machine into the resumable state before yielding, and avoid hooks before non-idempotent actions like pushes, counter increments, or lock acquisitions unless guarded. Dropping the statement at the yield must restore invariants through Drop or abort cleanup.