host: cards-as-types — the blog content block vocabulary as metamodel types

Seed the kg-card / content-on-sx block kinds as types: a 'card' root (subtype-of type) +
card-heading/text/image/quote/code/embed/callout as subtypes, each with its own fields
(host/blog--seed-card-type!). They appear in /meta (Types 11) and define (a) the editor's
future card palette and (b) the radar migrator's target vocabulary. Instances-as-blocks vs
instances-as-posts is a later decision — this is the vocabulary.

plans/NOTE-blog-types-for-radar.md: the TYPE CONTRACT for the loops/radar migration — a
blog post -> is-a article + typed field-values; body Ghost/Koenig cards -> these card-types.
Two paths mapped onto radar's duplicate->cutover->diverge (type-at-import vs type-in-diverge),
plus the open cards-as-blocks-vs-posts question for them to inform from the Ghost corpus.

Verified live-path (/meta Types 11, card-types with fields) + focused eval (type-defs has
card-image; fields src/alt/caption, heading level/text). Full blog conformance still blocked
by box contention; test added for a quiet re-run.

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

lib/host/tests/blog.sx

@@ -703,6 +703,19 @@
       "application/x-www-form-urlencoded" "title=Sneaky Rel"))
     (host/blog-exists? "sneaky-rel"))
   false)
+
+;; -- cards-as-types: the blog content block vocabulary --
+(host-bl-test "card-types are seeded as subtypes of card (in type-defs)"
+  (let ((defs (host/blog-type-defs)))
+    (list (contains? defs "card") (contains? defs "card-image") (contains? defs "card-heading")))
+  (list true true true))
+(host-bl-test "a card-type carries its fields"
+  (map (fn (f) (get f :name)) (host/blog-fields-of "card-image"))
+  (list "src" "alt" "caption"))
+(host-bl-test "/meta lists the card vocabulary with fields"
+  (let ((body (dream-resp-body (host-bl-app (host-bl-req "/meta")))))
+    (list (contains? body ">Image</a>") (contains? body "src:URL, alt:String")))
+  (list true true))
 (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)"