fix(isolation): distinguish accident links from same-numbered nodes

Prefer link endpoints for legacy accident IDs and allow explicit node selection. Read authoritative initial statuses and sources, verify source isolation, and separate direct isolation from newly disconnected supply nodes. Return validation errors as HTTP 422.

The node-first lookup misrouted adjacent Fengyang pipes 19025 and 19026 into unrelated regions. Regression cases fail against the previous algorithm and pass after this change.

app/native/wndb/gis/network_views.py

@@ -1,4 +1,4 @@
-"""Read-only projections backed by the GIS materialized-view query layer."""
+"""Read-only GIS projections and authoritative network topology snapshots."""
 
 from typing import Any
 
@@ -69,6 +69,46 @@ def get_network_link_nodes(name: str) -> list[str]:
     ]
 
 
+def get_valve_isolation_topology(name: str) -> tuple[list[str], list[str], list[str]]:
+    """Read links, closed statuses and sources from one consistent SQL snapshot.
+
+    Isolation must include model links without published geometries, and use
+    initial statuses rather than treating every link as open. UNION ALL keeps
+    source nodes in the same statement snapshot without repeating them for
+    every link or relying on materialized view refresh timing.
+    """
+    rows = read_all(
+        name,
+        """
+        SELECT l.id, l.link_type::text AS element_type,
+               l.start_node_id, l.end_node_id,
+               COALESCE(s.status::text, p.status::text) AS status
+        FROM network.links AS l
+        LEFT JOIN network.pipes AS p ON p.link_id = l.id
+        LEFT JOIN network.link_initial_settings AS s ON s.link_id = l.id
+        UNION ALL
+        SELECT n.id, n.node_type::text AS element_type,
+               NULL, NULL, NULL
+        FROM network.nodes AS n
+        WHERE n.node_type::text IN ('reservoir', 'tank')
+        """,
+    )
+    link_entries: list[str] = []
+    source_nodes: list[str] = []
+    closed_links: list[str] = []
+    for row in rows:
+        element_id = str(row["id"])
+        if row["element_type"] in {"reservoir", "tank"}:
+            source_nodes.append(element_id)
+        else:
+            link_entries.append(
+                f"{element_id}:{row['element_type']}:{row['start_node_id']}:{row['end_node_id']}"
+            )
+            if row["status"] == "CLOSED":
+                closed_links.append(element_id)
+    return link_entries, source_nodes, closed_links
+
+
 def get_major_pipe_nodes(name: str, diameter: int) -> list[str]:
     """Return large pipes in the established API wire format."""
     rows = read_all(