iter revert: back out the Iteration-discipline milestone (it.1 + it.2)

One forward iteration; main never rewound. 1ff7e81 (the pre-9973546
commit) is the per-region byte oracle — every reverted source/test
file is byte-identical to it; crates/ailang-check/src/lib.rs fully so.

Root cause being corrected: the Iteration-discipline milestone was an
over-escalation of fieldtest finding F1 (a [friction] item whose own
minimal recommendation was a DESIGN.md note). Its totality dichotomy
made the maximally-LLM-natural build(d:Int)=Node(1,build(d-1),
build(d-1)) inexpressible (it.3 BLOCKED); the only in-thesis escape
(A1/it.2b) conceded the language's first documented-unenforced
totality precondition — a purity-pillar dilution the user rejected in
favour of a full revert + rebuild.

Removed: Term::Loop/Term::Recur/LoopBinder; the verify_structural_
recursion guardedness pass + term_contains_loop + Diverge-injection +
the transitively-it.2 module_fns plumbing; the five Recur*/
NonStructuralRecursion CheckError variants (+ code() + the 3 dedicated
ctx() arms); the it.1 codegen loop-header/phi/back-edge + parallel
block_terminated setter; all Loop/Recur walker arms; 16 it.1/it.2
fixtures; 2 pin files; bench/it3-oracle/. Restored: 2 RC fixtures to
1ff7e81 content.

Surgically kept (not in 1ff7e81, landed with the milestone but
independently sound): feature-acceptance clause 3 in DESIGN.md and
skills/brainstorm/SKILL.md, with its worked example de-claimed from
"shipped" to hypothetical-illustration form; the F3 P2 todo.
bench/orchestrator-stats/2026-05-15-iter-it.{1,2,3}.json kept as
historical record (like journals/plans).

Sole net addition: an honest F1/F4 documented-idiom note in DESIGN.md
(the tail-recursive accumulator fallback; examples/mut_counter.ail),
guarded by a doc-presence test — "a documentation note is not a
reshape", asserts nothing at the typecheck level.

Roadmap: the Iteration-discipline block + blocking-fork section
removed; the genuine total-Int-recursion ambition preserved as a
deferred P2 milestone sequenced behind a future Nat/refinement-types
milestone (not abandoned — correctly sequenced after the type
machinery it needs). 2026-05-15-iteration-discipline.md carries a
superseded header; it.1/it.2/it.3 journals + plans stay as history.

Correctness gate PRISTINE: 164 surviving 1ff7e81-era fixtures
ail check/ail run byte-identical to pre-milestone behaviour (verified
against a 1ff7e81 worktree reference compiler, zero drift);
cargo test --workspace 600/0; zero residual it.1/it.2 production
surface.

Spec docs/specs/2026-05-16-iteration-discipline-revert.md (b3853bf),
plan docs/plans/2026-05-16-iter-revert.md (abf0013).

crates/ailang-codegen/src/escape.rs

@@ -201,17 +201,6 @@ fn walk(t: &Term, out: &mut NonEscapeSet) {
             walk(body, out);
         }
         Term::Assign { value, .. } => walk(value, out),
-        Term::Loop { binders, body } => {
-            for b in binders {
-                walk(&b.init, out);
-            }
-            walk(body, out);
-        }
-        Term::Recur { args } => {
-            for a in args {
-                walk(a, out);
-            }
-        }
         Term::Lit { .. } | Term::Var { .. } => {}
     }
 }
@@ -406,15 +395,6 @@ fn escapes(t: &Term, tainted: &BTreeSet<String>, in_tail: bool) -> bool {
             escapes(body, tainted, in_tail)
         }
         Term::Assign { value, .. } => escapes(value, tainted, false),
-        Term::Loop { binders, body } => {
-            for b in binders {
-                if escapes(&b.init, tainted, false) {
-                    return true;
-                }
-            }
-            escapes(body, tainted, in_tail)
-        }
-        Term::Recur { args } => args.iter().any(|a| escapes(a, tainted, false)),
     }
 }
 
@@ -544,26 +524,6 @@ fn collect_free_vars(t: &Term, bound: &mut BTreeSet<String>, out: &mut BTreeSet<
             }
             collect_free_vars(value, bound, out);
         }
-        // Iter it.1: loop binder names bind inside the body and later
-        // binder inits, mirroring `Term::Mut`. Recur args are uses.
-        Term::Loop { binders, body } => {
-            let mut newly: Vec<String> = Vec::new();
-            for b in binders {
-                collect_free_vars(&b.init, bound, out);
-                if bound.insert(b.name.clone()) {
-                    newly.push(b.name.clone());
-                }
-            }
-            collect_free_vars(body, bound, out);
-            for n in newly {
-                bound.remove(&n);
-            }
-        }
-        Term::Recur { args } => {
-            for a in args {
-                collect_free_vars(a, bound, out);
-            }
-        }
     }
 }