Bug

defer: true on side_effect declarations was completely non-functional. Deferred side effects never executed.

Root Cause

Inside fire!, the after_commit :_fosm_run_deferred_side_effects callback was registered on the model class after locked_record.update! had already been called. Since update! is the operation that triggers the after_commit callback chain, the dynamically-registered callback could never fire for the current transaction — it would only fire on some future unrelated update to any record of that class.

Additionally, the after_commit approach had two secondary problems:

1. Class pollution — every fire! call registered a one-shot callback on the model class, then cleaned it up with skip_callback. This is fragile and races with concurrent transactions on the same class.
2. Instance variable on wrong object — deferred effects were stored on locked_record, but _fosm_run_deferred_side_effects is called on self, making the instance variables inaccessible.

Fix

Replace the dynamic after_commit approach with direct execution after the transaction block:

• Store deferred effects in instance variables on self during the transaction
• Call _fosm_run_deferred_side_effects immediately after ActiveRecord::Base.transaction closes (i.e. after commit)
• Remove the after_commit registration and skip_callback cleanup entirely

This preserves the original intent — effects run post-commit, outside the transaction, so failures don't roll back the state change — without the callback ordering problem or class pollution.

Changes

• lib/fosm/lifecycle.rb — Store deferred effects on self; call _fosm_run_deferred_side_effects directly after transaction; remove after_commit/skip_callback
• test/models/race_condition_test.rb — Update comments to reflect new approach

Test Results

68 runs, 179 assertions, 0 failures, 0 errors, 4 skips

All existing tests pass, including the two cross-machine causal chain tests (smoke_test.rb, litmus_test.rb) that exercise deferred side effects end-to-end.