relations: route enumeration — all-paths (all simple directed paths a->b) + 9 tests

Cycle-safe DFS in explain.sx, complements shortest-path relations-path. 135/135.

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` → **126/126** (Phases 1–4 complete + extensions)
+`bash lib/relations/conformance.sh` → **135/135** (Phases 1–4 complete + extensions)
 
 ## Ground rules
 
@@ -108,9 +108,18 @@ lib/relations/federation.sx
   (lowest common ancestors — a set; tree → singleton, DAG → may be several),
   `topo-order` (Kahn-style; nil for cyclic kinds). New `lib/relations/tree.sx`,
   computed in SX over `reach`/`ancestors`/`rnode`. `lib/relations/tests/tree.sx`.
+- [x] **route enumeration** — `all-paths` (all simple directed paths a→b, not just
+  the shortest; cycle-safe DFS) in explain.sx. `lib/relations/tests/routes.sx`.
 
 ## Progress log
 
+- **Extension: route enumeration** (135/135). `relations-all-paths(db,a,b,kind)`
+  in explain.sx — every simple (no repeated node) directed path a→b, not just the
+  shortest one `relations-path` returns; DFS that skips nodes already on the
+  current path so cyclic data terminates; a=b → `((a))`, no route → `()`. Reuses
+  engine's `relations-concat-map`/`-eng-member?`/`children-of`. + `relations/all-paths`
+  wrapper, `lib/relations/tests/routes.sx` (9 tests: two-route diamond, single
+  route, no route, self, route-through-cycle, route count, kind isolation).
 - **Extension: tree/DAG queries** (126/126). New `lib/relations/tree.sx`:
   `relations-common-ancestors` (intersection of the two ancestor sets),
   `relations-lca` (common ancestors with no other common ancestor reachable below