documentation updates

docs/services/entity-extraction.md

@@ -131,6 +131,20 @@ check alone won't reject.
 > imperfectly — switch to `/[^\p{L}\p{N}\s]/gu` if the set gains non-ASCII
 > entries.
 
+**Regurgitation guard (`mentionedIn`):** the extraction prompt feeds the model
+a "known entities" hint block (the 20 most-recent entities) for spelling/type
+consistency. The small model (qwen2.5:3b) will sometimes echo that list back as
+if those entities appeared in the conversation — most visibly on contentless
+turns (a greeting produced fake extractions of unrelated authors, game titles,
+etc.). After parsing, each extracted name is checked against the actual
+`userMessage + aiResponse` text (case- and whitespace-normalized substring); any
+name not present is dropped before upsert. Since the prompt constrains names to
+short proper nouns, a genuinely-discussed entity appears verbatim while a
+regurgitated hint does not. Relationships referencing a dropped entity fall away
+automatically (they resolve against the surviving `entityMap`). A prompt line
+also tells the model the hint list is spelling-only — a backstop, with
+`mentionedIn` as the deterministic guarantee.
+
 ## Relationship Processing
 
 After all entities are saved, relationships are processed: