spec: prose-loop-binders — loop binders out of the body block

Form-B prose renders loop binders as bare `name = init;` statements
inside the `loop { … }` body, which reads as C/Rust re-init-every-
iteration semantics — a lie about a body the projection exists to
let the reader trust. Redesign: parenthesised init-list on the
keyword, `loop(acc = 0, i = 1) { … }`, positionally isomorphic to
`recur(...)`. Projection-only; loop/recur AST, Form A, JSON-AST,
typecheck, codegen, and the Form-A↔JSON round-trip invariant are
untouched. Step-7.5 grounding-check PASS. Roadmap entry opened P0
in-flight.

docs/roadmap.md

@@ -35,6 +35,20 @@ work progresses.
 
 ## P0 — In flight
 
+- [~] **\[milestone\]** Prose `loop` binders — projection redesign.
+  Form-B prose currently renders loop binders as `name = init;`
+  statements *inside* the `loop { … }` body, which misreads as
+  C/Rust re-init-every-iteration semantics. Move them to a
+  parenthesised init-list on the keyword — `loop(acc = 0, i = 1)
+  { … }` — positionally isomorphic to `recur(...)`. Projection-only:
+  one `ailang-prose` `write_term` `Term::Loop` arm + 2 snapshot
+  fixtures/tests; loop/recur AST, Form A, JSON-AST, typecheck,
+  codegen, and the Form-A↔JSON round-trip invariant all unchanged.
+  Spec'd + approved 2026-05-18; Step-7.5 grounding-check PASS. Plan
+  next.
+  - context: `docs/specs/2026-05-18-prose-loop-binders.md`;
+    surfaced from the loop/recur prose review (2026-05-18 chat).
+
 - [x] **\[milestone\]** Standalone `loop` / `recur` — CLOSED 2026-05-18.
   Strictly-additive strict-iteration surface, `recur` tail-position-only,
   no totality claim. Shipped: iter 1 `a179ec3` (additive AST nodes),