feat(rag): lite-model document summaries — non-markdown docs summarized at import, summary chunk retrieves and resolves to the full source doc

tests/integration/test_chat_api.py

@@ -72,6 +72,15 @@ class FakeRagLLM:
         self.embed_batches += 1
         return [_token_vec(t) for t in texts]
 
+    async def chat(
+        self, messages: list[dict[str, str]], model: str | None = None
+    ) -> str:
+        """Deterministic ``lite`` stand-in for the import-time summaries
+        (phase 30) — same convention as ``tests.fakes.FakeEmbedder.chat``."""
+        user = next((m["content"] for m in messages if m.get("role") == "user"), "")
+        first = user.split()
+        return "Summary of " + (first[0] if first else "<empty>")
+
     async def embed_one(self, text: str) -> list[float]:
         if self.embed_error is not None:
             raise self.embed_error