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>

plans/relations-on-sx.md

@@ -18,7 +18,7 @@ links. Reuses `lib/datalog/` — does not reimplement the engine.
 
 ## Status (rolling)
 
-`bash lib/relations/conformance.sh` → **147/147** (Phases 1–4 complete + extensions)
+`bash lib/relations/conformance.sh` → **158/158** (Phases 1–4 complete + extensions)
 
 ## Ground rules
 
@@ -114,9 +114,22 @@ lib/relations/federation.sx
   cleanup: retract every local edge touching a node, all kinds, both directions —
   for domain object deletion; leaves federated peer links alone). api.sx,
   `lib/relations/tests/bulk.sx`.
+- [x] **weakly-connected components** — `component` (the undirected cluster of a
+  node), `components` (partition of all nodes for a kind), `component-count`. In
+  tree.sx, reusing `ureach-bfs`. `lib/relations/tests/comp.sx`.
 
 ## Progress log
 
+- **Extension: weakly-connected components** (158/158). `relations-component`
+  (the undirected cluster containing a node = `ureach-bfs` from it),
+  `relations-components` (greedy partition: pop a remaining node, take its
+  component, repeat) and `relations-component-count`, in tree.sx, + `relations/...`
+  wrappers. `lib/relations/tests/comp.sx` (11 tests: cluster from either end, self-
+  loop as its own component, partition contents, count, kind isolation, api).
+  Engine surface now feels SATURATED — base roadmap + 5 graph-algorithm extensions
+  cover direct/transitive/undirected reach, paths (shortest + all routes), cycles,
+  roots/leaves, siblings/degree, ancestors/LCA/topo, components, federation, and
+  bulk lifecycle. Pacing down.
 - **Extension: bulk lifecycle** (147/147). `relations-relate-many!` (batch
   `dl-assert!` over a list of (src dst kind) triples) and `relations-unrelate-node!`
   (query `rel` for every edge with the node as src or dst, across all kinds, then