host: metamodel create-relation form (session-scoped) + keep load-rel-kinds! unrolled

Define a relation through the UI (metamodel editor surface 1, completing it):
POST /meta/new-relation creates a relation-post (is-a relation, :rel metadata) and
registers it via a runtime concat onto host/blog-rel-kinds — safe because the serving
handler has the IO resolver installed. /meta gains a '+ Relation' form (name, label,
symmetric). Verified: define 'Blocks' (symmetric) -> Relations(5), its editor renders on
edit pages, kind-spec + symmetric correct; auth-guarded.

SESSION-SCOPED: the relation-post + edges persist durably, but the rel-kinds registry
entry is lost on restart because load-rel-kinds! must stay UNROLLED — it runs at BOOT
where it is JIT-compiled but the IO resolver is NOT yet installed, so a dynamic loader
(map/reduce over instances-of 'relation' with a durable read per item) silently returns []
(verified: dynamic -> /meta Relations(0)). The serving-JIT HO-callback-perform fix only
engages with the resolver = serve time. Flagged to sx-vm-extensions (NOTE-render-diff-for-
vm-ext.md); they ACKed + are tracking the boot-resolver fix. Reverted the dynamic loader,
kept the unroll with a comment explaining why.

VERIFICATION NOTE: the full blog suite could not complete — the box is under extreme
contention from sibling loops (load 14, multiple full conformance + erlang/vm-ext rebuilds)
and the Datalog-heavy 140-test suite times out even at a 1800s cap. Verified instead two
ways: (1) live-path HTTP (real route + auth + editor render, ephemeral SX_SERVING_JIT=1),
(2) a focused in-process eval of the create-relation core (exists/is-a/kind-spec/symmetric/
registry-len = true,true,true,true,5). Prior full run was 140/140; changes since are purely
additive (handler + form + route + 3 tests). Re-run the blog suite when the box is quiet.

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

lib/host/tests/blog.sx

@@ -684,6 +684,25 @@
       "application/x-www-form-urlencoded" "title=Sneaky Type"))
     (host/blog-exists? "sneaky-type"))
   false)
+
+;; -- metamodel editor: define a relation through the UI (POST /meta/new-relation) --
+(host-bl-test "/meta has the create-relation form"
+  (contains? (dream-resp-body (host-bl-app (host-bl-req "/meta"))) "/meta/new-relation") true)
+(host-bl-test "POST /meta/new-relation creates + registers a relation (session-scoped)"
+  (begin
+    (host-bl-wapp (host-bl-send "POST" "/meta/new-relation" "Bearer good"
+      "application/x-www-form-urlencoded" "title=Blocks&label=Blocks&symmetric=on"))
+    (list (host/blog-exists? "blocks")
+          (host/blog-is-a? "blocks" "relation")
+          (not (nil? (host/blog--kind-spec "blocks")))
+          (host/blog--kind-symmetric? "blocks")))
+  (list true true true true))
+(host-bl-test "create-relation requires auth (unauthed -> not created)"
+  (begin
+    (host-bl-wapp (host-bl-send "POST" "/meta/new-relation" nil
+      "application/x-www-form-urlencoded" "title=Sneaky Rel"))
+    (host/blog-exists? "sneaky-rel"))
+  false)
 (host-bl-test "a post with no schema'd type is vacuously valid"
   (host/blog-type-valid? "ppost" "(p \"anything\")") true)
 (host-bl-test "edit-submit rejects content violating the type schema (not saved)"