Keep checkpoints aligned with PromptKit profiles

docs/internal/llm.md

@@ -41,6 +41,17 @@ identity, provider, and model values for manifest use. Successful completion
 responses and recorded profile manifests identify the adapter provider as
 `promptkit`.
 
+Before execution, the adapter also contributes a non-secret checkpoint
+fingerprint for the effective PromptKit profile source. It combines the
+identity of PromptKit's compiled-in profile catalog with a deterministic digest
+of every YAML profile in the configured profile directory, or of the configured
+profile file. The fingerprint contains neither profile content nor source
+paths. It covers both explicit binding profiles and prompt-selected defaults,
+so changing a model or other profile setting cannot reuse checkpoints created
+under the prior profile source. This cache identity is independent of durable
+profile provenance: run manifests continue to list only profiles actually
+observed during LLM calls.
+
 ## Shared Provider-Call Limit
 
 Production construction creates one PromptKit client and wraps it in one