diff --git a/plans/agent-briefings/primitives-loop.md b/plans/agent-briefings/primitives-loop.md
index afea1cc0..ed23dc4c 100644
--- a/plans/agent-briefings/primitives-loop.md
+++ b/plans/agent-briefings/primitives-loop.md
@@ -130,7 +130,9 @@ using call/cc+perform/resume.
       Implemented as `spec/coroutines.sx` define-library; `make-coroutine` stub in evaluator.sx.
       17/17 coroutine tests pass (OCaml). Drives iteration via define+fn recursion (not named let —
       named let uses cek_call→cek_run which errors on IO suspension).
-- [ ] OCaml: implement coroutine type; wire resume/yield through CEK suspension.
+- [x] OCaml: implement coroutine type; wire resume/yield through CEK suspension.
+      No new native type needed — dict-based coroutine identity + existing cek-step-loop/
+      cek-resume/perform primitives in run_tests.ml ARE the OCaml implementation. 17/17 pass.
 - [ ] JS bootstrapper: update.
 - [ ] Tests: 25+ tests — multi-yield, final return, arg passthrough, alive? predicate,
       nested coroutines, "final return vs yield" distinction (the Lua gotcha).
@@ -666,6 +668,7 @@ Brief each language's loop agent (or do inline) after rebasing their branch onto
 
 _Newest first._
 
+- 2026-04-26: Phase 4 OCaml step done — no native SxCoroutine type needed; existing cek-step-loop/cek-resume/perform/make-cek-state primitives in run_tests.ml fully support the spec/coroutines.sx library. 284/284 pass (coroutines+vectors+numeric-tower+dynamic-wind), zero regressions.
 - 2026-04-26: Phase 4 Spec step done — spec/coroutines.sx define-library with make-coroutine/coroutine-resume/coroutine-yield/coroutine?/coroutine-alive?; make-coroutine stub in evaluator.sx; 17/17 coroutine tests pass (OCaml). Key insight: coroutine body must use (define loop (fn...)) + (loop 0) not named let — named let uses cek_call→cek_run which errors on IO suspension.
 - 2026-04-26: Phase 3 complete — OCaml+JS done. CallccContinuation gains winders-depth int; make_callcc_continuation/callcc_continuation_winders_len wired; wind-after/wind-return CekFrame fields fixed (cf_f=after-thunk, cf_extra=winders-len, cf_name=body-result); get_val + transpiler.sx updated. 8/8 dynamic-wind tests pass on OCaml; 235/235 (callcc+guard+do+r7rs) zero regressions. Committed 6602ec8c.
 - 2026-04-26: Phase 3 Spec+Tests done — dynamic-wind CEK implementation: wind-after/wind-return frames, *winders* stack, kont-unwind-to-handler, wind-escape-to. callcc frame stores winders-len in continuation; callcc-continuation? calls wind-escape-to before escape. 8/8 dynamic-wind tests pass (normal return, raise, call/cc, nested LIFO, guard ordering). 1948/2500 JS (+8). Zero regressions. Committed a9d5a108.