Migrate TS reuse decisions onto EntryMeta side table and fix parseWith watermark.

Align D1 semantics: engine-side entryMeta drives tryReuse*; parseWith no longer
mutates consumer handles. Strip ext in ast-builder eq so cstBuilder ≡ parse
without the old W-path side effect.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: johnsoncodehk