fix: cluster edges render on left/right handles from approve flow

Cluster edges created via the pending -> approve path rendered on the top
handle instead of left/right, because the edge and its endpoints lost their
handle information on the way to the canvas.

- Approve resolver (scan.py) now returns each edge's type + source/target
  handle. Handle IDs are the bare slot-0 side names ('right'/'left'), the
  canonical stored form React Flow resolves to the correct side; a '-t' target
  id fails to resolve and falls back to the top handle.
- Frontend injectAutoEdges no longer hardcodes iot/bottom/top-t. It injects
  each edge with its real type + handles and bumps the referenced nodes'
  left/right handle counts (which default to 0) so the cluster endpoints exist.
  Logic extracted to a pure, tested util (applyAutoEdges).
- clusterEdges direct-import path uses the bare 'left' target to match.

Tests: new autoEdges unit tests; updated backend handle assertions.

ha-relevant: maybe

backend/app/api/routes/scan.py

@@ -642,16 +642,20 @@ async def _resolve_pending_links_for_ieee(
         if edge_design_id is None:
             first = (await db.execute(select(Design).order_by(Design.created_at).limit(1))).scalar()
             edge_design_id = first.id if first else None
-        # Edge shape by link source:
+        # Edge shape by link source. Handle IDs are the *bare* slot-0 side names
+        # (the canonical stored form — the save path normalizes '<side>-t' → the
+        # bare source id, and React Flow resolves the bare id to that side). A
+        # '-t' target id does not resolve here and RF falls back to the top
+        # handle, so never emit one.
         #   proxmox         → 'virtual' host→guest, vertical (bottom → top)
         #   proxmox_cluster → 'cluster' host↔host, horizontal (right → left)
         #   anything else   → 'iot' mesh link, vertical
         if link.discovery_source == "proxmox":
-            edge_type, src_handle, tgt_handle = "virtual", "bottom", "top-t"
+            edge_type, src_handle, tgt_handle = "virtual", "bottom", "top"
         elif link.discovery_source == "proxmox_cluster":
-            edge_type, src_handle, tgt_handle = "cluster", "right", "left-t"
+            edge_type, src_handle, tgt_handle = "cluster", "right", "left"
         else:
-            edge_type, src_handle, tgt_handle = "iot", "bottom", "top-t"
+            edge_type, src_handle, tgt_handle = "iot", "bottom", "top"
         edge = Edge(
             source=src_id,
             target=tgt_id,
@@ -663,7 +667,16 @@ async def _resolve_pending_links_for_ieee(
         db.add(edge)
         await db.flush()
         existing_pairs.add((src_id, tgt_id))
-        created.append({"id": edge.id, "source": src_id, "target": tgt_id})
+        # Return the edge's type + handles so the client injects it faithfully
+        # (a cluster edge must keep its right→left handles, not the iot default).
+        created.append({
+            "id": edge.id,
+            "source": src_id,
+            "target": tgt_id,
+            "type": edge_type,
+            "source_handle": src_handle,
+            "target_handle": tgt_handle,
+        })
         await db.delete(link)
 
     return created

backend/tests/test_proxmox_router.py

@@ -265,7 +265,9 @@ async def test_cluster_link_resolves_to_cluster_edge(db_session) -> None:
     edge = (await db_session.execute(select(Edge))).scalars().one()
     assert edge.type == "cluster"
     assert edge.source_handle == "right"
-    assert edge.target_handle == "left-t"
+    # Bare side name (canonical) so React Flow resolves it to the left side;
+    # a '-t' target would fall back to the top handle.
+    assert edge.target_handle == "left"
 
 
 @pytest.mark.asyncio

backend/tests/test_scan.py

@@ -1281,7 +1281,8 @@ async def test_approve_zigbee_creates_edge_when_other_endpoint_is_node(
     assert edges[0].source == coord.id
     assert edges[0].target == data["node_id"]
     assert edges[0].source_handle == "bottom"
-    assert edges[0].target_handle == "top-t"
+    # Bare side name (canonical stored form); renders at the top like before.
+    assert edges[0].target_handle == "top"
     assert edges[0].type == "iot"