feat: implement matching router with support for retrieval, reranking, and candidate explanation workflows

backend/src/routers/matching.py

@@ -90,30 +90,30 @@ async def trigger_match(
                 MatchResult.session_id == session_id if session_id else MatchResult.session_id.is_(None),
             )
         )
+
+        inserted_mrs = []
+        for i, item in enumerate(final_ranked):
+            mr = MatchResult(
+                id=uuid.uuid4(), jd_id=jd_id,
+                candidate_id=uuid.UUID(item["candidate_id"]),
+                session_id=session_id,
+                rank=i + 1,
+                stage1_score=item.get("stage1_score", 0),
+                stage2_score=item.get("stage2_score"),
+                final_score=item.get("final_score", 0),
+                component_scores=item.get("component_scores", {}),
+                gaps=item.get("gaps", []),
+            )
+            db.add(mr)
+            inserted_mrs.append(mr)
+
+        await db.commit()
     except Exception:
         await db.rollback()
         raise
 
     from ..workers.explain import generate_top_explanations
 
-    inserted_mrs = []
-    for i, item in enumerate(final_ranked):
-        mr = MatchResult(
-            id=uuid.uuid4(), jd_id=jd_id,
-            candidate_id=uuid.UUID(item["candidate_id"]),
-            session_id=session_id,
-            rank=i + 1,
-            stage1_score=item.get("stage1_score", 0),
-            stage2_score=item.get("stage2_score"),
-            final_score=item.get("final_score", 0),
-            component_scores=item.get("component_scores", {}),
-            gaps=item.get("gaps", []),
-        )
-        db.add(mr)
-        inserted_mrs.append(mr)
-
-    await db.commit()
-
     # Pre-generate LLM explanations async for the top 20 matches implicitly in background
     top_20_ids = [str(mr.id) for mr in inserted_mrs[:20]]
     if top_20_ids:
@@ -163,7 +163,15 @@ async def get_match_results(
     rows = result.all()
 
     if not rows:
-        raise HTTPException(status_code=404, detail="No match results found. Run POST /api/match/{jd_id} first.")
+        return MatchResponse(
+            jd_id=jd_id, 
+            jd_title=jd.title, 
+            jd_quality=jd.jd_quality or {}, 
+            weights_used=jd.custom_weights or {},
+            total_matched=0, 
+            results=[], 
+            session_id=session_id,
+        )
 
     results = []
     for mr, cand in rows: