fix(#622): any-state wildcard fires when composable sub-SM terminates

[PavelGuzenfeld]

Problem

When the outer SM is in a composable sub-state (a struct with public operator(), treated as sm<T>) and the sub-SM handles an event that terminates all its regions (reaches X), the outer wildcard transition (any + event<E> = state<S>) was never evaluated.

Root cause: get_state_mapping<sm<T>>::type::execute() short-circuits via || when sub_sm_mapping::execute() returns true — so fallback_event_mapping (the outer _ wildcard) is never tried, even after the sub-SM has terminated.

The author of #622 noted that the same SM declared as class (private operator(), not composable) worked correctly, because non-composable states go through the primary get_state_mapping template which always tries both state_mapping and any_state_mapping.

Fix

In get_state_mapping<sm<T>, TMappings, TUnexpected>::type::execute():

// Before
return sub_sm_mapping::execute(...) || fallback_event_mapping::execute(...);

// After
const auto sub_handled = sub_sm_mapping::execute(...);
if (sub_handled && !sub_sm<sm_impl<T>>::get(&subs).is_terminated()) {
  return true;  // sub-SM handled event and is still running
}
// sub-SM terminated or didn't handle — give outer wildcard a chance
return fallback_event_mapping::execute(...) || sub_handled;

get_id_safe<R,T> is added as a variadic-fallback variant of get_id that returns static_cast<R>(-1) when T is not in the state list. This makes is_terminated_impl safe to call on sub-SMs that have no X-terminating transitions (previously it would fail to compile for them). The value -1 can never equal a valid (non-negative) state ID, so is_terminated() correctly returns false for such SMs.

Test

test/ft/issue_622_any_state_nested.cpp:

• any_state_fires_after_nested_sub_sm_terminates: outer SM in composable sub_a; e1 terminates the sub-SM and the outer wildcard any + e1 = state_b must fire → outer SM in state_b.
• any_state_leaf_baseline: wildcard for non-composable (leaf) states works as before.

Verification

Toolchain	Standard	Result
GCC 14 (Docker)	C++14	33/33 (pre-existing C++14 static_assert failure unrelated to this PR, tracked by #698)
GCC 14 (Docker)	C++17	33/33 ✅
GCC 14 (Docker)	C++20	33/33 ✅
MSVC 19.51 (Wine)	C++20	compiles cleanly ✅

Closes #622.