Fix SSE route dependency and align architecture docs

backend/app/domain/retrieval/models.py

@@ -0,0 +1,29 @@
+"""Define domain models for retrieval."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+# Keep module behavior explicit so the backend flow stays easy to audit.
+
+
+
+@dataclass
+class RetrievalQuery:
+    """Represent the Retrieval Query type."""
+    query: str
+    top_k: int
+    filters: str | None = None
+
+
+@dataclass
+class RetrievedChunk:
+    """Represent the Retrieved Chunk type."""
+    chunk_id: str
+    doc_id: str
+    doc_name: str
+    content: str
+    score: float
+    section_title: str = ""
+    page_number: int = 0
+    metadata: dict[str, Any] = field(default_factory=dict)