Add bounded sources and strict YAML parsing

docs/internal/extraction.md

@@ -53,6 +53,14 @@ Assigned to the YAML/source implementation:
   ConfigKit's scalar grammar and limits, and replace raw parser errors with safe
   diagnostics. Narratio's application decoders and YAML node types are not copied.
 
+Implementation record (2026-09-06): the labeled byte/reader ownership and strict
+single-document cases above were generalized into `source.go`, `parse.go`, and
+`internal/yaml`. No production line was copied verbatim. ConfigKit adds byte and
+tree ceilings, shared atomic reader claims, regular-file checks, exact numeric
+lexemes, parser-depth calibration, ConfigKit-owned locations, safe diagnostic
+codes, and an AST import-boundary regression. Application typed decoding, parser
+errors, YAML node types, and session-specific loaders were not retained.
+
 ### Strict composition
 
 Assigned to document composition: