iter loop-recur.1: additive Term::Loop / Term::Recur / LoopBinder foundation

First of three iterations of the standalone loop/recur milestone
(spec 97c1ed1). loop/recur become real parseable / printable /
round-trippable / hash-stable strictly-additive AST nodes across
every no-wildcard exhaustive Term match in all six crates, plus
parse/print, prose arms, DESIGN.md + form_a.md schema blocks,
drift/coverage/hash anchors, and the spec's worked sum_to program
as a green round-trip fixture. NO typecheck semantics and NO real
codegen this iter by design: synth and lower_term are stubbed
CheckError::Internal / CodegenError::Internal exactly as mut.1
(real typecheck = iter 2, real loop-header/phi/back-edge = iter 3).

Two binding Boss design calls recorded in the plan header and the
journal: (1) verify_tail_positions "byte-unchanged" = its tail-app
verification role is unchanged, not its source — it is an
exhaustive no-wildcard match so two descent-only arms are
mandatory; acceptance evidence is the tail-app non-regression test.
(2) codegen is in iter-1 scope as stubs/pass-throughs because the
workspace must compile for cargo test --workspace.

Three plan-pseudo-vs-reality substitutions (serde Type::Con
literal, bare Int -> (con Int), unqualified LoopBinder) and one
recon-undercount integration-test site, all intent-preserving and
journalled. Boss forward-fix folded in: the committed specs
themselves wrote bare Int in the loop-binder snippets (parses as
Type::Var) — corrected the three headline snippets to (con Int) for
doc-honesty (no design/schema change).

cargo test --workspace 600 -> 608 / 0 red (Boss-reran
independently); iter13a + new loop_recur hash pins green.

crates/ailang-codegen/src/escape.rs

@@ -201,6 +201,17 @@ 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 { .. } => {}
     }
 }
@@ -395,6 +406,22 @@ 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 } => {
+            for a in args {
+                if escapes(a, tainted, false) {
+                    return true;
+                }
+            }
+            false
+        }
     }
 }
 
@@ -524,6 +551,24 @@ fn collect_free_vars(t: &Term, bound: &mut BTreeSet<String>, out: &mut BTreeSet<
             }
             collect_free_vars(value, bound, out);
         }
+        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);
+            }
+        }
     }
 }
 

crates/ailang-codegen/src/lambda.rs

@@ -505,6 +505,24 @@ impl<'a> Emitter<'a> {
                 }
                 Self::collect_captures(value, bound, captures, captures_set, builtins, top_level);
             }
+            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);
+                }
+            }
         }
     }
 

crates/ailang-codegen/src/lib.rs

@@ -1837,6 +1837,14 @@ impl<'a> Emitter<'a> {
                 ));
                 Ok(("0".into(), "i8".into()))
             }
+            // loop-recur iter 1: real codegen (loop-header block,
+            // per-binder phi, back-edge br) lands in iter 3. This
+            // iter stubs the dispatch so the workspace compiles; no
+            // loop/recur program is codegen'd in iter 1. Mirrors
+            // mut.1's lower_term stub.
+            Term::Loop { .. } | Term::Recur { .. } => Err(CodegenError::Internal(
+                "Term::Loop/Term::Recur lowering lands in loop-recur iter 3".into(),
+            )),
         }
     }
 
@@ -3093,6 +3101,13 @@ impl<'a> Emitter<'a> {
             // is exhaustive on Term so the arms must exist.
             Term::Mut { body, .. } => self.synth_with_extras(body, extras),
             Term::Assign { .. } => Ok(Type::unit()),
+            // loop-recur iter 1: a Term::Loop's static type is the
+            // body's type (mirror Term::Mut). Term::Recur does not
+            // fall through; a Unit stub is safe — this arm is never
+            // hit on the shipping path because lower_term stubs
+            // Loop/Recur, and iter 1 codegens no loop/recur program.
+            Term::Loop { body, .. } => self.synth_with_extras(body, extras),
+            Term::Recur { .. } => Ok(Type::unit()),
         }
     }
 }