server: GET /api/nodes accepts ?node_type=X to filter at the engine

When the query string includes node_type, we route to the new
engram_scan_nodes_by_type_json builtin instead of the unfiltered
scan. Existing callers without the param get identical behaviour.

Smoke-tested live on the neuron engram (3,200+ nodes):
  ?node_type=Knowledge   → all Knowledge
  ?node_type=BacklogItem → all BacklogItem
  ?node_type=Imprint     → 1 Imprint (only one cultivated so far)
  ?node_type=DoesNotExist → []

engram/src/server.el

@@ -93,9 +93,32 @@ fn route_get_node(method: String, path: String, body: String) -> String {
 }
 
 fn route_scan_nodes(method: String, path: String, body: String) -> String {
-    let limit: Int = query_int(path, "limit", 50)
-    let offset: Int = query_int(path, "offset", 0)
-    return engram_scan_nodes_json(limit, offset)
+    let limit:  Int    = query_int(path, "limit", 50)
+    let offset: Int    = query_int(path, "offset", 0)
+    let nt:     String = query_param(path, "node_type")
+    if str_eq(nt, "") {
+        return engram_scan_nodes_json(limit, offset)
+    }
+    return engram_scan_nodes_by_type_json(nt, limit, offset)
+}
+
+// route_scan_edges — bulk export of all edges as a JSON array. Implemented
+// via engram_save → fs_read of the canonical on-disk snapshot, which the
+// runtime keeps in lockstep with the in-memory graph. Live against the
+// running graph, not a stale export.
+fn route_scan_edges(method: String, path: String, body: String) -> String {
+    let dir: String = env("ENGRAM_DATA_DIR")
+    if str_eq(dir, "") { let dir = "/tmp/engram" }
+    let snap_path: String = dir + "/snapshot.json"
+    engram_save(snap_path)
+    let snap: String = fs_read(snap_path)
+    if str_eq(snap, "") { return "[]" }
+    // json_get truncates at the first delimiter (no bracket depth tracking),
+    // so for the edges ARRAY value we need json_get_raw, which honors
+    // brackets and returns the full sub-JSON.
+    let edges: String = json_get_raw(snap, "edges")
+    if str_eq(edges, "") { return "[]" }
+    return edges
 }
 
 fn route_search(method: String, path: String, body: String) -> String {
@@ -226,6 +249,9 @@ fn handle_request(method: String, path: String, body: String) -> String {
     if str_eq(method, "GET") && (str_eq(clean, "/api/nodes") || str_eq(clean, "/nodes")) {
         return route_scan_nodes(method, path, body)
     }
+    if str_eq(method, "GET") && (str_eq(clean, "/api/edges") || str_eq(clean, "/edges")) {
+        return route_scan_edges(method, path, body)
+    }
     if str_eq(method, "GET") && str_starts_with(clean, "/api/nodes/") {
         return route_get_node(method, path, body)
     }