What changed

• re-exported the supported read-only grammar helpers from the package root and locked that surface into the public API contract
• moved syntax-start and canonical parsing ownership back into context_compiler.grammar so engine.py no longer duplicates directive-start matching logic
• kept the grammar-to-engine parsed-directive seam explicitly internal and updated internal tests to point syntax-boundary checks at grammar

Why

• core grammar should be the single syntax authority inside this repository
• consumers that need grammar validation/rendering should rely on the supported grammar contract instead of duplicated syntax logic
• the engine should keep semantic/state behavior while depending on grammar through a clearly internal seam rather than overlapping syntax helpers
• related to Review public API mutation boundaries #201

Checklist

• pre-commit run (uv run pre-commit run --all-files)
• tests pass (uv run pytest)