Finalize bounded typed pipeline implementation

docs/internal/modules.md

@@ -23,8 +23,13 @@ implementation-owned values and injects dependencies. The spell extractor is
 typed over the canonical D&D model. D&D validators, merge, and normalize use
 typed variants; JSON representation validators use serialized requests; and
 unconditional validators expose separate chunk and typed variants. The D&D
-production registrar does not register raw spell-stage implementations in
-parallel.
+production registrar registers only the canonical typed spell implementations.
+
+Prepared extractors, extract validators, and codecs may be reused concurrently
+by the run-wide extract pool. Production implementations are immutable after
+construction: they retain only typed options, immutable assets, or the shared
+concurrency-safe LLM client. Implementations that introduce mutable state must
+synchronize that state without creating a separate provider scheduler.
 
 Specs expose capability and execution metadata without constructing an
 implementation. Registry entries separately expose option validation and