relations: weakly-connected components (component, components partition, count) + 11 tests

tree.sx, reuses ureach-bfs. 158/158 across 9 suites.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/relations/tree.sx

@@ -103,6 +103,37 @@
 
 ;; --- current-db convenience layer ---
 
+(define
+  relations-component
+  (fn
+    (db node kind)
+    (relations-ureach-bfs db kind (list node) (list node))))
+
+(define
+  relations-components-loop
+  (fn
+    (db kind remaining acc)
+    (if
+      (= (len remaining) 0)
+      acc
+      (let
+        ((comp (relations-component db (first remaining) kind)))
+        (relations-components-loop
+          db
+          kind
+          (filter (fn (n) (not (relations-eng-member? n comp))) remaining)
+          (append acc (list comp)))))))
+
+(define
+  relations-component-count
+  (fn (db kind) (len (relations-components db kind))))
+
+(define
+  relations-components
+  (fn
+    (db kind)
+    (relations-components-loop db kind (relations-nodes db kind) (list))))
+
 (define
   relations/common-ancestors
   (fn
@@ -116,3 +147,15 @@
 (define
   relations/topo-order
   (fn (kind) (relations-topo-order (relations-ensure-db!) kind)))
+
+(define
+  relations/component
+  (fn (node kind) (relations-component (relations-ensure-db!) node kind)))
+
+(define
+  relations/components
+  (fn (kind) (relations-components (relations-ensure-db!) kind)))
+
+(define
+  relations/component-count
+  (fn (kind) (relations-component-count (relations-ensure-db!) kind)))