content: typed block objects on smalltalk + 38 tests

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` → **0/0** (not yet started)
+`bash lib/content/conformance.sh` → **38/38** (Phase 1: typed blocks)
 
 ## Ground rules
 
@@ -57,7 +57,7 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 ```
 
 ## Phase 1 — Block document model
-- [ ] `block.sx` — typed block objects
+- [x] `block.sx` — typed block objects
 - [ ] `doc.sx` — ordered tree, apply edit op, structural moves
 - [ ] `render.sx` — block tree → HTML/SX
 - [ ] `api.sx` + tests + scoreboard + conformance.sh
@@ -76,7 +76,17 @@ lib/content/api.sx ── (content/edit) (content/render) (content/history) ─
 - [ ] tests: round-trip import/export, conflict on concurrent external edit
 
 ## Progress log
-(loop fills this in)
+
+- 2026-06-06 — Phase 1 `block.sx`: typed block objects as Smalltalk instances
+  (`CtBlock` hierarchy: text/heading/code/quote/image/embed/divider/list).
+  Type tag + accessors are message sends (polymorphic dispatch); fields are
+  immutable copy-on-write via functional `st-iv-set!` (history-safe). Added
+  `mk-*` constructors, `block?` predicate, `lib/content/conformance.sh` +
+  scoreboard. 38/38.
 
 ## Blockers
-(loop fills this in)
+
+- Smalltalk-only load chain (tokenizer/parser/runtime/eval) does **not** load
+  `lib/r7rs.sx`/`spec/stdlib.sx`, so r7rs aliases (`car`/`cdr`/`null?`) are
+  absent. Use base SX primitives (`first`/`rest`/`(= (len x) 0)`) in
+  `lib/content/**`. Not a substrate bug — just the load surface.