content: document validation (validate.sx) + 17 tests (294/294)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plans/content-on-sx.md

@@ -19,7 +19,7 @@ injected adapter, not core.
 
 ## Status (rolling)
 
-`bash lib/content/conformance.sh` → **277/277** (Phases 1–4 COMPLETE + extensions: HTML/SX escaping, Markdown, durable CRDT replication)
+`bash lib/content/conformance.sh` → **294/294** (Phases 1–4 COMPLETE + extensions: HTML/SX escaping, Markdown, durable CRDT replication, validation)
 
 ## Ground rules
 
@@ -80,9 +80,17 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 - [x] asSx wire string-escaping (`String>>sxEscaped`: \ and " in SX literals)
 - [x] Markdown render mode (`asMarkdown:` / `content/render doc "md"`)
 - [x] durable CRDT replication (`crdt-store.sx`: ops on persist, replay + converge)
+- [x] document validation (`validate.sx`: ids, per-type fields, duplicate ids)
 
 ## Progress log
 
+- 2026-06-07 — Extension: document validation (`validate.sx`). `content/validate`
+  returns issue dicts `{:id :kind :detail}` (empty = valid); `content/valid?`
+  and `content/issue-kinds` convenience. Checks block id (non-empty string),
+  per-type required fields/types (heading level number, image src/alt strings,
+  list ordered boolean + items list, etc.), unknown block types, and
+  document-level duplicate ids. Guards imports/edits/federated input. 17 tests;
+  suite 294/294.
 - 2026-06-07 — Extension: durable CRDT replication (`crdt-store.sx`), uniting
   Phase 2 (persist) + Phase 3 (CvRDT). Each replica appends its CRDT ops to its
   own stream (`crdt:<doc>:<replica>`); `crdt/replay` folds one log into a state,