blogimport: published-posts source contract + blog-side draft (76/76)

source.sx refactored to a single published-posts batch query returning full rows
(incl. lexical) — the existing post-by-id/slug DTO lacks lexical (sx_content/html
only), so the canonical lexical->blocks path needs a dedicated migration provider.
backfill-ids! now filters client-side (no extra query).

drafts/published-posts.sx + drafts/README.md: paste-ready blog-app change (defquery +
SqlBlogService.list_published_posts returning rows incl. raw lexical). README updated.
source 21/21; total 76/76.

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

lib/blogimport/drafts/published-posts.sx

@@ -0,0 +1,16 @@
+; DRAFT — proposed addition to blog/queries.sx (the blog app's internal-data surface).
+; Resolves the one blog-side gap for Q-M4: blogimport needs to enumerate published
+; posts AND read their raw lexical bodies. The existing post-by-id/slug/ids queries
+; return a PostDTO that carries sx_content/html but NOT lexical, so a dedicated
+; migration query that returns full rows (incl. lexical) is the minimal change.
+;
+; Paste this defquery into blog/queries.sx alongside the others, and add the matching
+; `list_published_posts` provider to SqlBlogService (see drafts/README.md).
+;
+; This file is a DRAFT artifact (not loaded by anything); it is parse-validated only.
+
+(defquery published-posts ()
+  "Enumerate every published, non-page blog post as a full row INCLUDING the raw
+   lexical body — the SX migration corpus (Q-D2). Read-only; used by the blogimport
+   backfill + at-rest verify. Newest-first."
+  (service "blog" "list-published-posts"))