# Handoff: native SX-island blog editor

> Handed off from the **host-on-sx** loop (2026-06-19). Build this in a
> **browser-capable session** (Playwright installed) — a reactive island only
> proves out when it hydrates in a browser; this worktree has no Playwright.

## Goal

A native **SX reactive island** WYSIWYG block editor for blog posts — replacing
the legacy `shared/static/scripts/sx-editor.js` (Koenig-era JS, ~2500 lines).
It edits blocks reactively and, on publish, emits **`sx_content`** (SX element
markup) + a title + status, and submits to the host's create endpoint.

## Architecture (decided this session)

- The editor is the **interactivity layer**, so it lives on the **`--http`
  island pipeline** (`sx.rose-ash.com`, which already SSRs + hydrates islands),
  **NOT** in the `http-listen` host (the host deliberately doesn't do island
  hydration — see `plans/host-on-sx.md` Phase 5).
- It **publishes to the host**: the host serves `blog.rose-ash.com` and owns the
  durable store + create/render. The editor is a docs-side island that talks to
  the host's API. Two cooperating SX servers: host = content/API/state, `--http`
  = interactive UI.

## The host contract (already live + proven)

`POST /new` on the host (`blog.rose-ash.com`) — **works today**:
- Body: **form-urlencoded** `title`, `sx_content`, `status` (`draft`/`published`).
- Behaviour: slug derived from title, post stored in the durable KV, **303
  redirect** to `/<slug>/`.
- `host/blog-form-submit` in `lib/host/blog.sx`; route `host/blog-open-create-routes`
  (currently UNGUARDED experimental — gate before real use).
- A **form POST** (303 redirect) needs **no CORS**. If the editor uses `fetch`
  instead, the host needs CORS on `/new` — the host loop can add `dream-cors-with`
  (`lib/dream/cors.sx`) in minutes; just ask.

## `sx_content` format — what to emit

SX **element markup**, rendered host-side by `render-page` → `render-to-html`,
**per block, guarded** (`host/blog-render` in `lib/host/blog.sx`). So:
- Top level is a fragment: `(<> (h2 "Title") (p "para " (strong "bold")) (ul (li "a") (li "b")))`.
- **Use standard tags `render-to-html` knows**: `p h1..h6 ul ol li blockquote
  code pre strong em a img figure hr br span div`. These render cleanly + fast.
- **AVOID the legacy `~kg-*` card components** — they show as `(unsupported
  block)` placeholders (the legacy editor emits bare `~kg-md` but the components
  are `~kg_cards/kg-md` — name drift we deliberately did NOT alias). If cards are
  wanted, define **canonical** card components the host loads (no bare-name shim).
- A bad/unknown block degrades to a placeholder, never crashes the page — but
  aim to emit only renderable markup.

## Build notes

- It's a `defisland` served as a `defpage` on `--http`. Example island:
  `sx/sx/home/stepper.sx`. Reactive primitives: `signal`/`deref`/`computed`/
  `effect` (see the signals spec).
- **SX island authoring gotchas** (CLAUDE.md "SX Island Authoring Rules"):
  multi-expr bodies need `(do …)`; `let` is parallel (nest for sequencing);
  reactive text needs `(deref (computed …))`; effects go in an inner `let`.
- A reasonable MVP: title input (signal) + an ordered list of block signals
  (type + text), add/remove/reorder, a few block types (paragraph, heading,
  list, quote, code), a **live preview** (computed → rendered), and a Publish
  that serialises blocks → `sx_content` and form-POSTs to the host's `/new`.
- **Test with `sx_playwright`** (inspect / hydrate / interact / trace-boot) —
  hydrate the island, simulate typing, assert the serialized `sx_content` and
  the live preview. Don't ship an island you haven't hydrated in a browser.

## Pointers

- Host ingest + render + page shell: `lib/host/blog.sx` (the `/new` POST is the
  target; `host/blog-render` shows exactly which markup renders).
- `render-page` (host's component renderer) + the static-page pattern:
  `lib/host/page.sx`, `plans/host-on-sx.md` Phase 5.
- Island example: `sx/sx/home/stepper.sx`. HTML renderer (tags it knows):
  `web/adapter-html.sx`. Legacy editor (reference only, being replaced):
  `shared/static/scripts/sx-editor.js`.
