Enforce deterministic translation pipeline and remove unsupported semantic fallback paths

[Copilot]

This change implements the roadmap direction to harden translation behavior without introducing an IR layer. It tightens determinism and reliability by making parse/plan/emit decisions stable and rejecting semantic holes instead of silently degrading.

• Deterministic parse selection

  • Added stable tie-breakers for parse result and alternation selection.
  • Canonicalized sequence fallback ordering and grammar rule discovery order to remove reflection/order variance.

• Planner fail-closed behavior for unsupported semantic targets

  • Removed placeholder insertion for unmapped required target semantic children.
  • Candidate mappings with unresolved semantic child projection are now marked unsupported and excluded.

• Deterministic output reproducibility gate

  • Added replay check in compilation flow to ensure repeated translation of the same input yields identical output/diagnostics.
  • Extended reliability policy with explicit output reproducibility requirement.

• Policy versioning surfaced in failures

  • Added reliability policy version field and included it in failure messages to pin behavior and aid regression triage.

• Determinism regression coverage

  • Added dedicated test project with deterministic replay and mapping-selection stability assertions, plus a deterministic failure-path assertion for unsupported mappings.

var translation = translator.TranslateDetailed(sourceDiagram.Root);
var replay = translator.TranslateDetailed(sourceDiagram.Root);
var reproducibleTranslationOutput = AreExecutionOutputsEquivalent(translation, replay);