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superseded header; it.1/it.2/it.3 journals + plans stay as history.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/lambda.rs

@@ -144,12 +144,6 @@ impl<'a> Emitter<'a> {
         let saved_mut_allocas = std::mem::take(&mut self.mut_var_allocas);
         let saved_pending_allocas = std::mem::take(&mut self.pending_entry_allocas);
         let saved_entry_marker = self.entry_block_end_marker.take();
-        // Iter it.1: a `loop` inside a lambda body scopes its header /
-        // phis to the closure's own body, not the outer fn's. Save and
-        // reset `loop_frames` (the exact mut.3 analogue to
-        // `mut_var_allocas` above) so a `Term::Recur` inside the thunk
-        // cannot back-edge to an outer fn's loop header.
-        let saved_loop_frames = std::mem::take(&mut self.loop_frames);
         // Iter 18d.4 fix: a lambda thunk is its own fn frame for
         // param-mode lookup. The outer fn's params are not in scope
         // inside the thunk; the thunk's own params are pushed below
@@ -264,7 +258,6 @@ impl<'a> Emitter<'a> {
         self.mut_var_allocas = saved_mut_allocas;
         self.pending_entry_allocas = saved_pending_allocas;
         self.entry_block_end_marker = saved_entry_marker;
-        self.loop_frames = saved_loop_frames;
 
         // 3. Emit allocation + capture filling + closure-pair packing
         //    in the OUTER body. Captures use 8 bytes each; closure-pair
@@ -512,27 +505,6 @@ impl<'a> Emitter<'a> {
                 }
                 Self::collect_captures(value, bound, captures, captures_set, builtins, top_level);
             }
-            // Iter it.1: loop binder names bind inside the body and
-            // later binder inits — they are NOT captures, mirroring
-            // the `Term::Mut` arm above. Recur args are uses.
-            Term::Loop { binders, body } => {
-                let mut newly_bound: Vec<String> = Vec::new();
-                for b in binders {
-                    Self::collect_captures(&b.init, bound, captures, captures_set, builtins, top_level);
-                    if bound.insert(b.name.clone()) {
-                        newly_bound.push(b.name.clone());
-                    }
-                }
-                Self::collect_captures(body, bound, captures, captures_set, builtins, top_level);
-                for n in newly_bound {
-                    bound.remove(&n);
-                }
-            }
-            Term::Recur { args } => {
-                for a in args {
-                    Self::collect_captures(a, bound, captures, captures_set, builtins, top_level);
-                }
-            }
         }
     }