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>

plans/relations-as-posts.md

@@ -68,14 +68,34 @@ Sequence: finish the schema language (Slices 6–7) → the two UI surfaces + re
 data and define a real domain through the UI. The slices below are the schema language; this is
 what it's *for*.
 
-### Endgame — the whole platform as a typed domain (the strangler's finish line)
+### Endgame — the whole platform as a typed domain (greenfield, not a strangler)
 
 Not just the blog: the entire rose-ash platform — **store, events, orders, cart, …** — is
 expressible as type + relation definitions in this one metamodel. `Product`, `Event`, `Order`,
 `Ticket` are types; "cart has line-items", "order for an event", "ticket of an event" are
 relations with signatures (cardinality = a cart has many line-items, a ticket belongs to one
-event). This is the completion of the host-on-sx strangler off Quart (`[[project_host_on_sx]]`):
-define the domain schema as data instead of porting each service's bespoke models.
+event). This is NOT a strangler off Quart (`[[project_host_on_sx]]`) — it's a **greenfield,
+SX-native system**: define the domain schema as data from first principles, then **port the data
+once at the end** (define-then-port), rather than reimplementing each service's bespoke models
+endpoint-by-endpoint. The strangler's compatibility machinery (JSON mirrors, route/model parity,
+incremental contracts) is dropped — it was tax, not value, for a system that doesn't *correspond*
+to the old one.
+
+### SX all the way out — no JSON on the internal wire
+
+The platform speaks **SX/SXTP end to end**, both directions, browser included — JSON survives only
+at the ActivityPub federation edge (JSON-LD, a published external standard).
+
+| Layer | SX-native form |
+|-------|----------------|
+| Page render | HTML (the document itself) |
+| Data reads | `text/sx` via the `serialize` primitive (`host/ok`/`host/error` → `host/sx-status`) |
+| Write bodies | `text/sx` parsed via `sxtp/parse` (was JSON / form-urlencoded) |
+| Browser → server | the engine posts `text/sx` (boosted forms serialise fields to SX wire); form-urlencoded survives only as the **no-engine / pre-hydration fallback** + the **login bootstrap** handshake |
+| Federation edge | JSON-LD (ActivityPub — the *only* JSON) |
+
+The blog **JSON CRUD `/posts`** (POST/PUT/DELETE) is **deleted**, not converted: it was a pure
+old-contract REST mirror; writes go through the HTML editor forms + SXTP.
 
 Three honest additions store/events surface (the blog didn't need them):