host: relation enumeration via a static slug list (graph scan was fragile on live)

host/blog-in "relation" "is-a" (a reduce over ALL edges) returned a partial set on
the live store (many edges), so only one relation editor rendered. Enumerate the
relations from a fixed slug list instead — deterministic; the metadata still lives
on the relation-posts (loaded into the cache). rel-kinds maps kind-spec over the
list and drops any uncached.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/host/blog.sx

@@ -102,17 +102,23 @@
 ;; rel-kinds / kind-symmetric? then read the cache (pure); the relation-posts stay
 ;; the durable source of truth. host/blog-load-rel-kinds! re-reads them.
 (define host/blog--rel-cache (dict))
+;; the relation slugs — a small fixed set. (Enumerating them from the graph via
+;; host/blog-in "relation" "is-a" proved fragile on the live store: that reduce over
+;; ALL edges returned a partial set. A static list is deterministic; the metadata
+;; still lives on the relation-posts. Add a relation here + a seed-rel! call.)
+(define host/blog--rel-slugs (fn () (list "related" "is-a" "subtype-of" "tagged")))
 (define host/blog-load-rel-kinds!
   (fn ()
     (for-each
       (fn (kind)
         (let ((m (get (host/blog-get kind) :rel)))
           (when m (dict-set! host/blog--rel-cache kind (merge {:kind kind} m)))))
-      (host/blog-in "relation" "is-a"))))   ;; relations are flat: direct is-a is enough
+      (host/blog--rel-slugs))))
 ;; spec = the cached :rel metadata + :kind; nil for a non-relation (relate validates).
 (define host/blog--kind-spec (fn (kind) (get host/blog--rel-cache kind)))
 (define host/blog-rel-kinds
-  (fn () (map (fn (k) (get host/blog--rel-cache k)) (keys host/blog--rel-cache))))
+  (fn () (filter (fn (s) (not (nil? s)))
+           (map host/blog--kind-spec (host/blog--rel-slugs)))))
 (define host/blog--kind-symmetric?
   (fn (kind) (let ((s (host/blog--kind-spec kind))) (and s (get s :symmetric)))))