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+# Markpub content member — design
+
+**Date:** 2026-07-06
+**Status:** approved
+
+## Motivation
+
+The `site.standard.document` records ghoststandard writes carry no `content`
+union member at all — only `textContent`, a plain-text extraction of the
+Ghost post HTML. A standard.site viewer can show a preview but cannot render
+the post body.
+
+markpub.at (`at.markpub.markdown` / `at.markpub.text`, repo AramZS/markpub.at)
+is a community lexicon for exactly this slot, designed to nest inside
+standard.site documents. gifthood.org adopted it on 2026-07-06
+(spec `2026-07-06-markpub-content-shape-design.md` in that repo); this brings
+ghoststandard to the same contract so any markpub-aware reader can render
+posts from either project.
+
+Unlike gifthood, this is purely additive: there is no legacy content shape to
+keep reading, no read path at all (ghoststandard is a write-only bridge —
+Ghost is the source of truth, deletes go through the local SQLite mapping),
+and no blob problem (Ghost posts reference images by absolute URL on Ghost's
+own hosting, so they survive as plain `![](url)` markdown).
+
+## The wrinkle: derived markdown
+
+Ghost's Admin API emits `html`, `lexical`/`mobiledoc`, and `plaintext` — never
+markdown (since Ghost 5, markdown is just a card type inside Lexical). So the
+emitted markdown is **derived** from `post.html` via turndown + the GFM
+plugin. Consequences accepted during brainstorming:
+
+- Standard blog content (headings, prose, links, images, lists, code, tables)
+  converts cleanly. Exotic Ghost cards degrade: embed iframes vanish (no text
+  content), bookmark cards collapse to links, galleries flatten to image
+  lines. Acceptable — `textContent` has the same limits today.
+- `flavor: "gfm"` is declared (turndown's GFM plugin output).
+- `renderingRules` is **omitted** — ghoststandard never renders from this
+  markdown (Ghost renders from Lexical), and the lexicon says to leave the
+  field out in that case. This deliberately differs from gifthood, where
+  markdown is the source and `renderingRules: "marked"` is a true statement.
+
+## Decisions (settled during brainstorming)
+
+1. **Converter: turndown + turndown-plugin-gfm** — de-facto standard,
+   extensible rule system for Ghost's kg-cards. (Ghost emitting markdown
+   directly was checked and ruled out; see above.)
+2. **Tests: mirror gifthood.** Vendor the two markpub lexicon JSONs as
+   fixtures and validate the emitted member with `@atproto/lexicon`. This
+   introduces the repo's first test setup (vitest).
+3. **One targeted kg-card rule**, everything else turndown defaults. Ghost
+   wraps every editor card in `<figure class="kg-card kg-*-card">`; a single
+   rule for captioned image figures covers the common case without a
+   per-card-type maintenance treadmill.
+4. **Emitted fields:** `$type`, `text: { markdown }`, `flavor: "gfm"`.
+   `renderingRules`, `textBlob`, `facets`, `lenses`, `frontMatter` omitted
+   (all optional; nothing consumes them — YAGNI).
+5. **Structure: a dedicated content-shape module** (`src/lib/content-shape.ts`),
+   matching gifthood's layout — one file owns the union member and the
+   turndown configuration, so future markpub evolution touches one place.
+
+## Out of scope
+
+- Any upstream markpub proposal (that conversation is driven from gifthood).
+- Changes to `textContent`, cover-image handling, codeinjection, webhooks, or
+  any other document field — the `content` member is the sole record change.
+- Rendering or reading markdown back (no read path exists).
+- Per-site opt-out of the content member.
+
+## 1. New module: `src/lib/content-shape.ts`
+
+- `MARKPUB_MARKDOWN_TYPE = 'at.markpub.markdown'`.
+- A module-level configured `TurndownService`: `headingStyle: 'atx'`,
+  `codeBlockStyle: 'fenced'`, GFM plugin applied (tables, strikethrough).
+- One rule for Ghost captioned-image figures
+  (`<figure class="kg-card kg-image-card">` containing `img` + `figcaption`):
+  image line followed by the caption on its own line. All other markup rides
+  turndown defaults.
+- `buildMarkpubContent(html: string): Record<string, unknown> | null` —
+  returns `null` when the input HTML is empty/whitespace-only, when the
+  *converted markdown* comes out empty/whitespace-only (e.g. an embed-only
+  post), **or if turndown throws** (conversion failure is logged and
+  swallowed; a conversion bug must never fail a sync — the record simply
+  omits `content`). Otherwise:
+
+  ```ts
+  {
+    $type: 'at.markpub.markdown',
+    text: { markdown },
+    flavor: 'gfm',
+  }
+  ```
+
+## 2. Write side: `transform.ts`
+
+`ghostPostToRecord` builds the member from `post.html` and attaches it
+alongside the other optional fields:
+
+```ts
+const content = buildMarkpubContent(post.html ?? '');
+if (content) record.content = content;
+```
+
+A comment notes that the `site.standard.document` content union is
+`closed: false`, so the member needs no lexicon registration — the value is
+the shared `$type`. `textContent` stays exactly as-is (it serves
+search/preview consumers; the markdown serves renderers).
+
+## 3. Dependencies and typing
+
+- Runtime deps: `turndown`, `turndown-plugin-gfm`.
+- Dev deps: `@types/turndown`, `vitest`, `@atproto/lexicon` (versions pinned
+  from `npm view <pkg> version` at implementation time).
+- `turndown-plugin-gfm` ships no types: add an ambient declaration to the
+  existing `src/types.d.ts` (same loose-shim pattern as `@tryghost/admin-api`
+  and `html-to-text`).
+- New package script: `"test": "vitest run"` — the repo's first.
+
+## 4. Vendored lexicons + tests
+
+- Copy `src/lexicons/markpub/{markdown,text}.json` and the fixtures README
+  verbatim from gifthood.org (source: AramZS/markpub.at, MIT,
+  `dist/lexicons/at/markpub/`, commit `9b53a3a8f93d`, fetched 2026-07-06).
+  Fixtures only — never loaded at runtime; a schema drift on refresh breaks
+  `npm test`, acting as a tripwire rather than a production dependency.
+- New `src/lib/content-shape.test.ts`:
+  - loads the vendored schemas into a `Lexicons` instance and asserts
+    `buildMarkpubContent(html)` output passes validation for
+    `at.markpub.markdown`;
+  - conversion cases: prose/headings/links, kg-image-card figure with
+    caption, code card → fenced block, GFM table, embed iframe → dropped
+    (and an embed-only post → `null`), empty HTML → `null`.
+- New `src/lib/transform.test.ts`: the record carries `content` for a post
+  with HTML and omits it for a post without.
+
+## 5. Migration: `gs backfill`
+
+No new mechanism. After deploy, run `gs backfill` once per site — it re-syncs
+every published post via `putRecord` with stable rkeys (the Ghost post id),
+so every record gains the `content` member in place. Spot-check afterward:
+`content.$type`, `content.text.markdown` renders sensibly, `textContent`
+unchanged.
+
+README gets one line in the "What ghoststandard does" bullet noting the post
+body travels as `at.markpub.markdown` content.
+
+## 6. Error handling & testing posture
+
+No new failure modes: the writer emits a constant shape or nothing, and the
+conversion guard in `buildMarkpubContent` means a turndown failure degrades
+to today's behavior (record without `content`). Record size is a non-issue —
+the markdown roughly doubles the existing `textContent` payload, far below
+PDS record limits for blog-sized posts.
+
+Gates: `npm run typecheck` and `npm test` before every commit. Live pass:
+dev publish → record shows the markpub member → `gs backfill` → spot-check.