diff --git a/plans/agent-briefings/primitives-loop.md b/plans/agent-briefings/primitives-loop.md
index b00be7a5..71dbd98a 100644
--- a/plans/agent-briefings/primitives-loop.md
+++ b/plans/agent-briefings/primitives-loop.md
@@ -465,13 +465,13 @@ Needed by Haskell `Rational`, CL, and any language doing fraction arithmetic.
 Needed by: Common Lisp, Smalltalk, Erlang integer formatting.
 
 Steps:
-- [ ] Audit which trig / math functions are already in `spec/primitives.sx`; note gaps.
-- [ ] Spec + OCaml + JS: implement missing trig (`sin`/`cos`/`tan`/`asin`/`acos`/`atan`/`exp`/`log`).
-- [ ] Spec + OCaml + JS: `quotient`/`remainder`/`modulo` with correct negative semantics.
-- [ ] Spec + OCaml + JS: `gcd`/`lcm`.
-- [ ] Spec + OCaml + JS: radix variants of `number->string`/`string->number`.
-- [ ] Tests: 40+ tests in `spec/tests/test-math.sx`.
-- [ ] Commit: `spec: math completeness — trig, quotient/remainder/modulo, gcd/lcm, radix`
+- [x] Audit which trig / math functions are already in `spec/primitives.sx`; note gaps.
+- [x] Spec + OCaml + JS: implement missing trig (`sin`/`cos`/`tan`/`asin`/`acos`/`atan`/`exp`/`log`).
+- [x] Spec + OCaml + JS: `quotient`/`remainder`/`modulo` with correct negative semantics.
+- [x] Spec + OCaml + JS: `gcd`/`lcm`.
+- [x] Spec + OCaml + JS: radix variants of `number->string`/`string->number`.
+- [x] Tests: 40+ tests in `spec/tests/test-math.sx`.
+- [x] Commit: `spec: math completeness — trig, quotient/remainder/modulo, gcd/lcm, radix`
 
 ---
 
@@ -748,6 +748,7 @@ _Newest first._
 - 2026-04-25: Phase 1 spec step done — all 10 vector primitives in spec/primitives.sx have full :as type annotations, :returns, :doc; make-vector optional fill param added.
 - 2026-04-25: Phase 1 OCaml step done — bounds-checked vector-ref/set!, vector-copy now accepts optional start/end, spec/primitives.sx doc updated. 10/10 r7rs vector tests pass, 4747 total (394 pre-existing hs-upstream fails unchanged).
 - 2026-04-25: Phase 0 complete — stopped CL/APL/Ruby/Tcl loops (all 4 idle at shell); confirmed E38 (tokenizer :end/:line) and E39 (WebWorker stub) both have implementation commits.
+- 2026-05-01: Phase 15 complete — math completeness. stdlib.math module: sin/cos/tan/asin/acos/atan(1-2 args)/exp/log/expt/quotient/gcd/lcm/number->string(radix)/string->number(radix). OCaml atan updated for optional 2nd arg. Strict radix parsing in JS string->number. 44 tests in test-math.sx, all pass. JS 2311/4801, OCaml 4547/5629. be2b11ac.
 - 2026-05-01: Phase 14 OCaml done — Eof + Port{PortInput/PortOutput} in sx_types.ml; 15 port primitives in sx_primitives.ml; raw_serialize updated; 4532/4532 (+39, zero regressions). 8ba0a33f.
 - 2026-05-01: Phase 14 Spec+JS+Tests+Commit done — port type {_port,_kind,_source/_buffer,_pos,_closed}; eof singleton; 15 primitives in spec/primitives.sx (stdlib.ports) + platform.py; 39/39 tests in test-ports.sx. Committed 3d8937d7. OCaml step next.
 - 2026-05-01: Phase 13 OCaml done — Char of int in sx_types.ml; #\ reader in sx_parser.ml; all char primitives in sx_primitives.ml; fixed get_val for Integer n list indexing (was Number-only); fixed raw_serialize for Integer/Char. 4493/4493 (+43, zero regressions). b939becd.