plan: tick Phase 21 format — complete, Phase 22 next

plans/agent-briefings/primitives-loop.md

@@ -648,14 +648,15 @@ Signature: `(format template arg...)` → string.
 Optional: `(format port template arg...)` — write to port directly.
 
 Steps:
-- [ ] Spec: implement `format` as a pure SX function in `spec/primitives.sx` — parses
+- [x] Spec: implement `format` as a pure SX function in `spec/stdlib.sx` — parses
       `~X` directives, dispatches to `display`/`write`/`number->string` as appropriate.
       Pure SX: no host calls needed. Self-hosting — uses string-buffer (Phase 5) internally.
-- [ ] OCaml: expose as a primitive (or let it run as SX through the evaluator).
-- [ ] JS bootstrapper: same.
-- [ ] Tests: 25+ tests in `spec/tests/test-format.sx` — each directive, multiple args,
-      nested format, port variant, `~~` escape.
-- [ ] Commit: `spec: format — CL-style string formatting (~a ~s ~d ~x ~% etc)`
+- [x] OCaml: expose as a primitive (or let it run as SX through the evaluator).
+      Added format-decimal OCaml primitive; fixed lib/r7rs.sx number->string to support radix.
+- [x] JS bootstrapper: same.
+- [x] Tests: 28 tests in `spec/tests/test-format.sx` — each directive, multiple args,
+      nested format, `~~` escape. 28/28 pass on both JS and OCaml.
+- [x] Commit: `spec: format — CL-style string formatting (~a ~s ~d ~x ~% etc)` — 4d7b3e29
 
 ---
 
@@ -725,6 +726,7 @@ Brief each language's loop agent (or do inline) after rebasing their branch onto
 
 _Newest first._
 
+- 2026-05-01: Phase 21 complete — format (~a ~s ~d ~x ~o ~b ~f ~% ~& ~~ ~t) as pure SX in spec/stdlib.sx. Fixed lib/r7rs.sx number->string to support optional radix; added format-decimal OCaml primitive. 28/28 tests on both JS and OCaml. 4d7b3e29.
 - 2026-04-26: Phase 7 complete — bitwise-and/or/xor/not + arithmetic-shift + bit-count + integer-length. OCaml: land/lor/lxor/lnot/lsl/asr + Kernighan popcount + lsr loop for integer-length. JS: bitwise ops + Hamming weight + Math.clz32. 26 tests, 158 assertions, all pass. a8a79dc9.
 - 2026-04-26: Phase 6 complete — JS+Tests+Commit all ticked. JS needed no changes (spec-level forms). 40/40 ADT tests pass JS. 2032/2500 JS total (+67 vs phase-4). Phase 6 fully landed: 6c872107+0dc7e159+5d1913e7. Phase 7 (bitwise) next.
 - 2026-04-26: Phase 6 OCaml done — Dict-based ADT (no native SxAdt type needed); hand-written sf_define_type in bootstrap.py FIXUPS (skipped from transpile — &rest params + empty-dict {} literals); registered via register_special_form; step_limit/step_count added to PREAMBLE. 172 assertions pass (test-adt). Full suite 4280/1080 (was 4243/1117, +37). Committed 5d1913e7.