Fix issue_253: clear nested defer queue on sub-state-machine exit

[gabewillen]

Summary

• clear deferred events owned by a nested sub-state-machine when transitioning out of that sub-state-machine
• reset sub-state-machine defer processing state on exit
• add a focused regression test (test_issue_253) reproducing and validating the original issue

Details

• fixed leak/stale replay behavior from defer within nested state machines isn't dropped upon exit of nested state machine boost-ext/sml#253
• behavior now matches expectation: deferred events in nested SM do not survive sub-SM exit/re-entry

Validation

• ran ./scripts/quality_gates.sh
• all quality gates passed (format, clang-tidy, regression matrix, sanitizers, coverage, benchmark smoke)

[Copilot]

Pull request overview

Fixes boost-ext#253 by ensuring deferred events belonging to a nested sub-state-machine don’t leak across sub-SM exit/re-entry, and adds a focused functional test to prevent regressions.

Changes:

• Add a new FT regression test validating that nested sub-SM deferred events are cleared on exit/re-entry.
• Update composite-state initialization to recurse into nested composite sub-state-machines.
• Clear a sub-state-machine’s defer queue and reset its defer-processing state when transitioning out of that sub-state-machine.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
include/boost/sml.hpp	Adds defer-queue clearing + defer-processing reset on sub-SM exit; recurses composite initialization.
test/ft/issue_253.cpp	New regression test reproducing issue boost-ext#253 and validating fixed behavior.
test/ft/CMakeLists.txt	Registers the new test_issue_253 executable/test with CTest.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.