host: SX-native wire — reads + write bodies are text/sx, JSON CRUD deleted

Greenfield SX-native pivot (NOT a strangler): the host speaks SX/SXTP end to end;
JSON only at the future ActivityPub federation edge.

- OUTPUT: host/json-status -> host/sx-status — every host/ok/host/error response is
  text/sx via the serialize primitive (NOT application/json). Flips feed, relations,
  blog reads. Tests assert the SX envelope ({:ok true :data ...}).
- DELETE the blog JSON CRUD /posts (POST/PUT/DELETE) + bearer-based host/blog--protect:
  a pure old-contract REST mirror. Create/edit go through the HTML editor forms;
  programmatic writes speak SXTP. FOLLOW-UP: no browser delete route yet (was JSON-only,
  no UI) — add POST /:slug/delete + cascade edge cleanup when the metamodel UI needs it.
- INPUT: host/sx-body (sxtp.sx) parses a text/sx request body to a string-keyed dict
  (parse-safe + sxtp/-normalize). feed POST + relations attach/detach read it.
- UNIFIED field reader host/fields / host/field: text/sx body OR urlencoded form by
  content-type. The blog form handlers (new/edit/relate/unrelate) + login read through
  it — additive, urlencoded still works (no-engine / bootstrap fallback).

Conformance 290/290 (11 suites). Retires the strangler framing in the plan; adds the
'SX all the way out' wire table. The engine half (browser posts text/sx) follows.

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

lib/host/tests/handler.sx

@@ -18,48 +18,48 @@
 ;; ── host/ok ────────────────────────────────────────────────────────
 (host-hd-test "ok status 200" (dream-status (host/ok "x")) 200)
 (host-hd-test
-  "ok content-type json"
+  "ok content-type sx"
   (dream-resp-header (host/ok "x") "content-type")
-  "application/json")
+  "text/sx; charset=utf-8")
 (host-hd-test
   "ok envelope ok:true"
-  (contains? (dream-resp-body (host/ok "x")) "\"ok\":true")
+  (contains? (dream-resp-body (host/ok "x")) ":ok true")
   true)
 (host-hd-test
   "ok envelope carries data"
-  (contains? (dream-resp-body (host/ok "hi")) "\"data\":\"hi\"")
+  (contains? (dream-resp-body (host/ok "hi")) ":data \"hi\"")
   true)
 
 ;; ── host/ok-status ─────────────────────────────────────────────────
 (host-hd-test "ok-status custom" (dream-status (host/ok-status 201 "y")) 201)
 (host-hd-test
   "ok-status data"
-  (contains? (dream-resp-body (host/ok-status 201 "y")) "\"data\":\"y\"")
+  (contains? (dream-resp-body (host/ok-status 201 "y")) ":data \"y\"")
   true)
 
 ;; ── host/error ─────────────────────────────────────────────────────
 (host-hd-test "error status" (dream-status (host/error 404 "nope")) 404)
 (host-hd-test
   "error ok:false"
-  (contains? (dream-resp-body (host/error 404 "nope")) "\"ok\":false")
+  (contains? (dream-resp-body (host/error 404 "nope")) ":ok false")
   true)
 (host-hd-test
   "error message"
-  (contains? (dream-resp-body (host/error 404 "nope")) "\"error\":\"nope\"")
+  (contains? (dream-resp-body (host/error 404 "nope")) ":error \"nope\"")
   true)
 (host-hd-test
-  "error content-type json"
+  "error content-type sx"
   (dream-resp-header (host/error 500 "boom") "content-type")
-  "application/json")
+  "text/sx; charset=utf-8")
 
-;; ── host/json-status ───────────────────────────────────────────────
+;; ── host/sx-status ─────────────────────────────────────────────────
 (host-hd-test
-  "json-status arbitrary status"
-  (dream-status (host/json-status 418 {:a 1}))
+  "sx-status arbitrary status"
+  (dream-status (host/sx-status 418 {:a 1}))
   418)
 (host-hd-test
-  "json-status encodes body"
-  (contains? (dream-resp-body (host/json-status 200 {:a 1})) "\"a\":1")
+  "sx-status serializes body"
+  (contains? (dream-resp-body (host/sx-status 200 {:a 1})) ":a 1")
   true)
 
 ;; ── host/query-int ─────────────────────────────────────────────────