looplab / fsm

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fix: clear the transition when the context is canceled

transitionFunc returns early when ctx.Err() != nil, but does not clear
f.transition on the way out — only the completed path below it does. Since
f.transition was already published before the context was ever checked, the FSM is
left in transition permanently: every later Event returns InTransitionError, Can()
returns false, and Transition() cannot help either, because it re-runs this same
closure and takes this same early return. Only constructing a new FSM recovers.

A state whose leave callback cancels is spared, because leaveStateCallbacks
returning CanceledError clears the flag. A state with no callbacks at all is not —
so whether a canceled context bricks the FSM depends on whether the state you
happen to be leaving has a callback registered.

Clears it with the same lock the completed path takes, and leaves e.Err untouched,
so Event still returns the context error to the caller as before.

Fixes #115.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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