bugfix: mono cursor misalignment at poly-free-fn Var with class-constrained Forall

When `synth` visits a `Term::Var v` where v is a polymorphic free fn
whose `Type::Forall` carries class constraints (e.g. `print : forall a.
Show a => ...`, `lt`/`le`/`gt`/`ge : forall a. Ord a => ...`), it
pushes BOTH a class `ResidualConstraint` for each constraint AND a
`FreeFnCall` observation at the same Var site. The mono walkers
(`interleave_slots` collection-side and `rewrite_mono_calls`
rewrite-side) consumed only ONE slot per such Var, leaving the
class-residual cursor misaligned for every subsequent class-method
call in the same body. The next `eq`/`compare` Var in the body then
consumed the leftover `Show T` / `Ord T` slot and was mis-rewritten —
codegen reported `call prelude.show__Bool arg type mismatch: expected
i1, got i64` (or the Int dual).

Fix: new `poly_free_fn_constraint_counts_for_module` registry in
mono.rs (sibling to `poly_free_fn_names_for_module`) maps each
synth-visible poly-free-fn name to its declared constraint count.
Threaded into `collect_residuals_ordered`, `interleave_slots`, and
`rewrite_mono_calls`. Both walkers now advance the cursor by 1 + N
(FreeFn slot + N class-residual fillers) at every poly-free-fn Var.

RED test `print_with_class_method_arg_does_not_misalign_mono_cursor`
(crates/ail/tests/show_print_e2e.rs) + fixture
examples/print_eq_arg_repro.ail pin the bug — body `(app print (app
eq 1 2))` previously crashed at codegen, now prints "false".

Bug surfaced 2026-05-14 during the rpe.1 BLOCKED orchestrator run;
existed in latent form since iter 24.3 (the poly-free-fn-with-class-
constraint synth shape was new there). No schema / codegen / DESIGN.md
changes. cargo test --workspace: 564 / 0 / 3.

bench/orchestrator-stats/2026-05-14-iter-bugfix-mono-cursor-print-with-class-method-arg.json

@@ -0,0 +1,12 @@
+{
+  "iter_id": "bugfix-mono-cursor-print-with-class-method-arg",
+  "date": "2026-05-14",
+  "mode": "mini",
+  "outcome": "DONE",
+  "tasks_total": 1,
+  "tasks_completed": 1,
+  "reloops_per_task": { "1": 0 },
+  "review_loops_spec": 0,
+  "review_loops_quality": 0,
+  "blocked_reason": null
+}

crates/ail/tests/show_print_e2e.rs

@@ -72,3 +72,36 @@ fn print_user_adt_runs_end_to_end() {
     // IntBox that unwraps via match + int_to_str).
     assert_eq!(stdout, "7", "got: {stdout:?}");
 }
+
+/// RED pin (rpe-bug-1, 2026-05-14): `(app print <arg>)` where `<arg>`
+/// contains a class-method call (here `eq 1 2 : Bool`) must lower
+/// cleanly. The iter 24.3 rewire taught `synth` to push a `Show T`
+/// residual for `print`'s declared constraint at the same `Var` site
+/// where the poly-free-fn observation is pushed (see
+/// `crates/ailang-check/src/lib.rs` lines 2908-2960). But the
+/// mono-rewrite walker in `crates/ailang-check/src/mono.rs`
+/// (`interleave_slots` and `rewrite_mono_calls`) treats every
+/// poly-free-fn `Var` as consuming exactly one free-fn slot — it does
+/// not advance the class-residual cursor for the constraint that was
+/// pushed at the same site. The consequence is a one-position
+/// misalignment: the *next* class-method call in the body consumes
+/// the `Show T` slot, rewriting `eq` → `show__Bool`. Codegen then
+/// reports `call prelude.show__Bool arg type mismatch: expected i1,
+/// got i64`.
+///
+/// Property protected: a `print` call whose argument contains a
+/// class-method invocation lowers to a valid IR call sequence — the
+/// `eq` (or other class-method) call is rewritten to its correct
+/// mono symbol, not to a stale `Show T` residual symbol.
+///
+/// Fixture `examples/print_eq_arg_repro.ail` exercises the shape
+/// `(app print (app eq 1 2))`. Expected stdout: `"false"` (Show Bool
+/// of `eq 1 2` → false). This test is GREEN once the cursor
+/// alignment in `interleave_slots` / `rewrite_mono_calls` is fixed
+/// to advance the class cursor for constraints carried by a
+/// poly-free-fn Var.
+#[test]
+fn print_with_class_method_arg_does_not_misalign_mono_cursor() {
+    let stdout = build_and_run("print_eq_arg_repro.ail");
+    assert_eq!(stdout, "false", "got: {stdout:?}");
+}

crates/ailang-check/src/mono.rs

@@ -178,16 +178,34 @@ pub fn monomorphise_workspace(ws: &Workspace) -> Result<Workspace> {
         // Iter 23.4: precompute the per-module poly-free-fn name
         // set used as the rewrite walker's second predicate.
         let poly_free_fns = poly_free_fn_names_for_module(&ws_owned, &env_mod, mname);
+        // 2026-05-14 bugfix: per-poly-free-fn-name constraint count,
+        // used by both walkers to advance their cursors past the
+        // synth-Var-arm's class-residual pushes (see
+        // [`poly_free_fn_constraint_counts_for_module`]).
+        let poly_free_fn_ccounts =
+            poly_free_fn_constraint_counts_for_module(&ws_owned, &env_mod, mname);
         let n_defs = ws_owned.modules[mname].defs.len();
         for i in 0..n_defs {
             let ordered: Vec<Option<MonoTarget>> = {
                 let m = &ws_owned.modules[mname];
                 let d = &m.defs[i];
                 match d {
-                    Def::Fn(f) => collect_residuals_ordered(f, mname, &env_mod, &poly_free_fns)?,
+                    Def::Fn(f) => collect_residuals_ordered(
+                        f,
+                        mname,
+                        &env_mod,
+                        &poly_free_fns,
+                        &poly_free_fn_ccounts,
+                    )?,
                     Def::Const(c) => {
                         let pseudo = const_as_pseudo_fn(c);
-                        collect_residuals_ordered(&pseudo, mname, &env_mod, &poly_free_fns)?
+                        collect_residuals_ordered(
+                            &pseudo,
+                            mname,
+                            &env_mod,
+                            &poly_free_fns,
+                            &poly_free_fn_ccounts,
+                        )?
                     }
                     _ => continue,
                 }
@@ -206,6 +224,7 @@ pub fn monomorphise_workspace(ws: &Workspace) -> Result<Workspace> {
                         &mut f.body,
                         &env.method_to_candidate_classes,
                         &poly_free_fns,
+                        &poly_free_fn_ccounts,
                         mname,
                         &ordered,
                         &mut cursor,
@@ -217,6 +236,7 @@ pub fn monomorphise_workspace(ws: &Workspace) -> Result<Workspace> {
                         &mut c.value,
                         &env.method_to_candidate_classes,
                         &poly_free_fns,
+                        &poly_free_fn_ccounts,
                         mname,
                         &ordered,
                         &mut cursor,
@@ -338,6 +358,52 @@ fn poly_free_fn_names_for_module(
     out
 }
 
+/// Bugfix 2026-05-14 (`bugfix-mono-cursor-print-with-class-method-arg`):
+/// per-module map from poly-free-fn name (in the exact spellings
+/// produced by [`poly_free_fn_names_for_module`] — bare same-module,
+/// implicit-import bare, and dot-qualified `alias.name`) to the number
+/// of class constraints carried by that fn's `Type::Forall`.
+///
+/// Both mono walkers ([`interleave_slots`] and [`rewrite_mono_calls`])
+/// must advance their cursors by `1 + N` at a poly-free-fn `Var` site
+/// where `N` is the constraint count: the synth Var-arm (see
+/// `crates/ailang-check/src/lib.rs` iter 24.3 block) pushes one
+/// `ResidualConstraint` per declared constraint at the same site where
+/// it pushes the `FreeFnCall` observation, so the slot-channel cursors
+/// would otherwise drift by `N` on every poly-free-fn-with-constraints
+/// `Var`.
+fn poly_free_fn_constraint_counts_for_module(
+    ws: &Workspace,
+    env: &crate::Env,
+    mname: &str,
+) -> BTreeMap<String, usize> {
+    let mut out: BTreeMap<String, usize> = BTreeMap::new();
+    // 1. Same-module poly fns.
+    if let Some(m) = ws.modules.get(mname) {
+        for d in &m.defs {
+            if let Def::Fn(f) = d {
+                if let Type::Forall { constraints, .. } = &f.ty {
+                    out.insert(f.name.clone(), constraints.len());
+                }
+            }
+        }
+    }
+    // 2 + 3. Imported modules' poly fns: bare AND dot-qualified.
+    if let Some(imports) = env.module_imports.get(mname) {
+        for (alias_or_name, target_mod) in imports {
+            if let Some(target_globals) = env.module_globals.get(target_mod) {
+                for (n, t) in target_globals {
+                    if let Type::Forall { constraints, .. } = t {
+                        out.insert(n.clone(), constraints.len());
+                        out.insert(format!("{alias_or_name}.{n}"), constraints.len());
+                    }
+                }
+            }
+        }
+    }
+    out
+}
+
 /// Iter 22b.3: workspace-wide `class-name -> ClassDef` index.
 /// Used by the fixpoint to look up the matching class definition
 /// when synthesising a fn.
@@ -1005,6 +1071,7 @@ fn rewrite_mono_calls(
     body: &mut Term,
     method_to_candidate_classes: &BTreeMap<String, BTreeSet<String>>,
     poly_free_fns: &BTreeSet<String>,
+    poly_free_fn_ccounts: &BTreeMap<String, usize>,
     caller_module: &str,
     ordered_targets: &[Option<MonoTarget>],
     cursor: &mut usize,
@@ -1021,10 +1088,31 @@ fn rewrite_mono_calls(
             // `method_to_candidate_classes`. Class disambiguation
             // (which class declared the resolved method) lives in the
             // residual slot the cursor consumes, not here.
+            //
+            // 2026-05-14 bugfix: a poly-free-fn `Var` whose source
+            // `Type::Forall` carries `N` class constraints consumes
+            // `1 + N` slots, not 1: the synth Var-arm pushes one
+            // `ResidualConstraint` per constraint (driving an entry
+            // into the `class_slots` channel) AT THE SAME SITE as the
+            // single `FreeFnCall` observation. The slot at `*cursor`
+            // is the FreeFn slot used for the actual rename; the
+            // following `N` slots are filler class slots — they exist
+            // only to keep the post-Var cursor positions aligned for
+            // later class-method `Var`s in the body. Class-method
+            // `Var`s themselves stay at advance-by-1 (synth pushes
+            // exactly one residual and no FreeFnCall).
             let is_class_method = method_to_candidate_classes.contains_key(name);
             let is_poly_free_fn = !is_class_method && poly_free_fns.contains(name);
             let should_advance = (is_class_method || is_poly_free_fn) && !locals.contains(name);
             if should_advance {
+                // Capture the constraint count BEFORE the rename
+                // below mutates `name`; lookup keys are the synth-
+                // visible spelling.
+                let n_filler = if is_poly_free_fn {
+                    poly_free_fn_ccounts.get(name).copied().unwrap_or(0)
+                } else {
+                    0
+                };
                 // The outer `Some` means the cursor slot exists; the inner
                 // `Some` means the observation at that slot is concrete.
                 // A `Some(None)` slot is a residual / non-concrete
@@ -1045,19 +1133,19 @@ fn rewrite_mono_calls(
                     };
                     *name = new_name;
                 }
-                *cursor += 1;
+                *cursor += 1 + n_filler;
             }
         }
         Term::App { callee, args, .. } => {
-            rewrite_mono_calls(callee, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(callee, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             for a in args {
-                rewrite_mono_calls(a, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+                rewrite_mono_calls(a, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             }
         }
         Term::Let { name, value, body } => {
-            rewrite_mono_calls(value, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(value, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             let inserted = locals.insert(name.clone());
-            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             if inserted {
                 locals.remove(name);
             }
@@ -1070,32 +1158,32 @@ fn rewrite_mono_calls(
                     params_inserted.push(p.clone());
                 }
             }
-            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             for p in &params_inserted {
                 locals.remove(p);
             }
-            rewrite_mono_calls(in_term, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(in_term, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             if name_inserted {
                 locals.remove(name);
             }
         }
         Term::If { cond, then, else_ } => {
-            rewrite_mono_calls(cond, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
-            rewrite_mono_calls(then, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
-            rewrite_mono_calls(else_, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(cond, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(then, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(else_, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
         }
         Term::Do { args, .. } => {
             for a in args {
-                rewrite_mono_calls(a, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+                rewrite_mono_calls(a, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             }
         }
         Term::Ctor { args, .. } => {
             for a in args {
-                rewrite_mono_calls(a, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+                rewrite_mono_calls(a, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             }
         }
         Term::Match { scrutinee, arms } => {
-            rewrite_mono_calls(scrutinee, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(scrutinee, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             for Arm { pat, body } in arms {
                 let binders = pattern_binders(pat);
                 let mut inserted: Vec<String> = Vec::new();
@@ -1104,7 +1192,7 @@ fn rewrite_mono_calls(
                         inserted.push(b.clone());
                     }
                 }
-                rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+                rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
                 for b in &inserted {
                     locals.remove(b);
                 }
@@ -1117,21 +1205,21 @@ fn rewrite_mono_calls(
                     inserted.push(p.clone());
                 }
             }
-            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
             for p in &inserted {
                 locals.remove(p);
             }
         }
         Term::Seq { lhs, rhs } => {
-            rewrite_mono_calls(lhs, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
-            rewrite_mono_calls(rhs, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(lhs, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(rhs, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
         }
         Term::Clone { value } => {
-            rewrite_mono_calls(value, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(value, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
         }
         Term::ReuseAs { source, body } => {
-            rewrite_mono_calls(source, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
-            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(source, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
+            rewrite_mono_calls(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, caller_module, ordered_targets, cursor, locals);
         }
         Term::Lit { .. } => {}
     }
@@ -1190,6 +1278,7 @@ pub(crate) fn collect_residuals_ordered(
     module_name: &str,
     env: &crate::Env,
     poly_free_fns: &BTreeSet<String>,
+    poly_free_fn_ccounts: &BTreeMap<String, usize>,
 ) -> Result<Vec<Option<MonoTarget>>> {
     let (rigids, inner_ty): (Vec<String>, Type) = match &f.ty {
         Type::Forall { vars, constraints: _, body } => (vars.clone(), (**body).clone()),
@@ -1335,6 +1424,7 @@ pub(crate) fn collect_residuals_ordered(
         &f.body,
         &env.method_to_candidate_classes,
         poly_free_fns,
+        poly_free_fn_ccounts,
         &class_slots,
         &free_fn_slots,
         &mut class_cur,
@@ -1360,6 +1450,7 @@ fn interleave_slots(
     term: &Term,
     method_to_candidate_classes: &BTreeMap<String, BTreeSet<String>>,
     poly_free_fns: &BTreeSet<String>,
+    poly_free_fn_ccounts: &BTreeMap<String, usize>,
     class_slots: &[Option<MonoTarget>],
     free_fn_slots: &[Option<MonoTarget>],
     class_cur: &mut usize,
@@ -1378,22 +1469,39 @@ fn interleave_slots(
                     out.push(slot);
                     *class_cur += 1;
                 } else {
+                    // 2026-05-14 bugfix: a poly-free-fn Var consumes
+                    // `1 + N` slots — the FreeFn slot (drives the
+                    // rewrite walker's rename) followed by `N` filler
+                    // class slots, where `N` is the constraint count
+                    // of this fn's source `Type::Forall`. Synth's
+                    // Var-arm pushes one `ResidualConstraint` per
+                    // declared constraint AT THIS SITE before pushing
+                    // the `FreeFnCall` observation; without consuming
+                    // the corresponding class slots here, the class-
+                    // method cursor drifts by `N` for every following
+                    // class-method Var in the body.
                     let slot = free_fn_slots.get(*free_cur).cloned().unwrap_or(None);
                     out.push(slot);
                     *free_cur += 1;
+                    let n_filler = poly_free_fn_ccounts.get(name).copied().unwrap_or(0);
+                    for _ in 0..n_filler {
+                        let filler = class_slots.get(*class_cur).cloned().unwrap_or(None);
+                        out.push(filler);
+                        *class_cur += 1;
+                    }
                 }
             }
         }
         Term::App { callee, args, .. } => {
-            interleave_slots(callee, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(callee, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             for a in args {
-                interleave_slots(a, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+                interleave_slots(a, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             }
         }
         Term::Let { name, value, body } => {
-            interleave_slots(value, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(value, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             let inserted = locals.insert(name.clone());
-            interleave_slots(body, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             if inserted {
                 locals.remove(name);
             }
@@ -1406,32 +1514,32 @@ fn interleave_slots(
                     params_inserted.push(p.clone());
                 }
             }
-            interleave_slots(body, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             for p in &params_inserted {
                 locals.remove(p);
             }
-            interleave_slots(in_term, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(in_term, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             if name_inserted {
                 locals.remove(name);
             }
         }
         Term::If { cond, then, else_ } => {
-            interleave_slots(cond, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
-            interleave_slots(then, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
-            interleave_slots(else_, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(cond, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(then, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(else_, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
         }
         Term::Do { args, .. } => {
             for a in args {
-                interleave_slots(a, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+                interleave_slots(a, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             }
         }
         Term::Ctor { args, .. } => {
             for a in args {
-                interleave_slots(a, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+                interleave_slots(a, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             }
         }
         Term::Match { scrutinee, arms } => {
-            interleave_slots(scrutinee, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(scrutinee, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             for Arm { pat, body } in arms {
                 let binders = pattern_binders(pat);
                 let mut inserted: Vec<String> = Vec::new();
@@ -1440,7 +1548,7 @@ fn interleave_slots(
                         inserted.push(b.clone());
                     }
                 }
-                interleave_slots(body, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+                interleave_slots(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
                 for b in &inserted {
                     locals.remove(b);
                 }
@@ -1453,21 +1561,21 @@ fn interleave_slots(
                     inserted.push(p.clone());
                 }
             }
-            interleave_slots(body, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
             for p in &inserted {
                 locals.remove(p);
             }
         }
         Term::Seq { lhs, rhs } => {
-            interleave_slots(lhs, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
-            interleave_slots(rhs, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(lhs, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(rhs, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
         }
         Term::Clone { value } => {
-            interleave_slots(value, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(value, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
         }
         Term::ReuseAs { source, body } => {
-            interleave_slots(source, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
-            interleave_slots(body, method_to_candidate_classes, poly_free_fns, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(source, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
+            interleave_slots(body, method_to_candidate_classes, poly_free_fns, poly_free_fn_ccounts, class_slots, free_fn_slots, class_cur, free_cur, locals, out);
         }
         Term::Lit { .. } => {}
     }

docs/journals/2026-05-14-iter-bugfix-mono-cursor-print-with-class-method-arg.md

@@ -0,0 +1,95 @@
+# iter bugfix-mono-cursor-print-with-class-method-arg — `(app print (app eq …))` no longer rewrites the inner class-method to a stale `Show T` symbol
+
+**Date:** 2026-05-14
+**Started from:** 05e4c04e3ba74f3382216ff3ea285e3fb1e3a45d
+**Status:** DONE
+**Tasks completed:** 1 of 1
+
+## Summary
+
+The iter 24.3 `synth` Var-arm pushes BOTH a class `ResidualConstraint`
+for each declared constraint AND a `FreeFnCall` observation at the
+same poly-free-fn `Var` site (`crates/ailang-check/src/lib.rs` ≈ 2908–
+2966). The two mono walkers in `crates/ailang-check/src/mono.rs`,
+however, were each consuming exactly one slot per `Var`: at a
+poly-free-fn `Var` they popped one `free_fn_slot` and zero
+`class_slot`s. Every constraint on a poly-free-fn-with-constraints
+left a leftover class slot, so the next class-method `Var` in the
+same body consumed the wrong slot — the residual that belonged to
+`print`'s `Show T` constraint got cursor-aligned with the inner `eq`
+`Var`, and codegen reported `call prelude.show__Bool arg type
+mismatch: expected i1, got i64`.
+
+The fix advances both walkers' cursors by `1 + N` at a poly-free-fn
+`Var` whose source `Type::Forall` carries `N` class constraints. A
+new sibling helper `poly_free_fn_constraint_counts_for_module`
+mirrors `poly_free_fn_names_for_module`'s three-source spelling
+contract (same-module / implicit-import bare / dot-qualified
+`alias.name`) and produces a `BTreeMap<String, usize>` from synth-
+visible name to declared-constraint count. The map is threaded into
+the rewrite-phase loop alongside `poly_free_fns` and passed to both
+`rewrite_mono_calls` and `interleave_slots`.
+
+In `interleave_slots`, a poly-free-fn `Var` now pushes the `FreeFn`
+slot first (this is what the rewrite walker reads for the rename),
+then `N` filler entries drawn in order from `class_slots` (consumed
+only to keep `class_cur` aligned). In `rewrite_mono_calls`, the
+`Var`-arm captures `n_filler` from the count map BEFORE the rename
+mutates `name` (lookup keys are the synth-visible spelling), reads
+the slot at `*cursor` as before, then advances by `1 + n_filler`.
+Class-method `Var`s stay at advance-by-one (synth pushes exactly one
+residual and no `FreeFnCall`).
+
+## Per-task notes
+
+- task 1: write/verify the cursor-alignment fix.
+  - Reproduced RED at `print_with_class_method_arg_does_not_misalign_mono_cursor`
+    with the exact failure mode stated in the carrier:
+    `call prelude.show__Bool arg type mismatch: expected i1, got i64`.
+  - Added `poly_free_fn_constraint_counts_for_module` helper
+    immediately after `poly_free_fn_names_for_module`; identical
+    name-source contract, returning constraint counts instead of a
+    presence set.
+  - Threaded `poly_free_fn_ccounts: &BTreeMap<String, usize>` into
+    `collect_residuals_ordered`, `interleave_slots`, and
+    `rewrite_mono_calls` (signatures + every recursive call site).
+  - `interleave_slots::Term::Var` poly-free-fn branch: after pushing
+    the `FreeFn` slot, drain `N` entries from `class_slots` and push
+    them as fillers in `out`, advancing `class_cur` by `N`.
+  - `rewrite_mono_calls::Term::Var`: compute `n_filler` from the
+    count map before the rename mutation, then `*cursor += 1 +
+    n_filler`. Class-method `Var`s are guarded with `if
+    is_poly_free_fn { … } else { 0 }`.
+  - RED `print_with_class_method_arg_does_not_misalign_mono_cursor`
+    flips to GREEN with stdout `false` as predicted by the fixture
+    docstring.
+  - Full `cargo test --workspace` passes 564 / 564 (= 563 baseline
+    from `clippy-sweep` + the 1 new mini-mode RED). Zero
+    regressions across any of the existing show / mono / typeclass
+    test suites.
+
+## Concerns
+
+(none)
+
+## Known debt
+
+(none — the constraint set is a single new sibling helper plus a
+new threaded argument; the two-walker symmetry remains the invariant
+the existing comments already document.)
+
+## Files touched
+
+- `crates/ailang-check/src/mono.rs` — the fix (helper + two walker
+  signatures + Var-arm cursor advancement + recursive-call
+  threading).
+- `crates/ail/tests/show_print_e2e.rs` — RED pin
+  `print_with_class_method_arg_does_not_misalign_mono_cursor`
+  (committed by `/debug` upstream of this iter; flips RED → GREEN
+  here).
+- `examples/print_eq_arg_repro.ail` — RED fixture (committed by
+  `/debug` upstream; consumed by the pin).
+
+## Stats
+
+bench/orchestrator-stats/2026-05-14-iter-bugfix-mono-cursor-print-with-class-method-arg.json

examples/print_eq_arg_repro.ail

@@ -0,0 +1,6 @@
+(module print_eq_arg_repro
+  (fn main
+    (doc "RED-pin fixture for the iter 24.3 cursor-misalignment bug. `(app print <arg>)` where `<arg>` itself contains a class-method call (here `eq`) causes the mono-rewrite cursor to consume the `Show T` residual pushed by `print`'s poly-free-fn observation as if it were the slot for the inner class method. Result: the inner `eq` Var is rewritten to `prelude.show__Bool` instead of `prelude.eq__Int`, and codegen reports `call prelude.show__Bool arg type mismatch: expected i1, got i64`. Bug surfaced 2026-05-14 during the rpe.1 BLOCKED orchestrator run; root cause is `crates/ailang-check/src/mono.rs::interleave_slots` not advancing the class-residual cursor when visiting a poly-free-fn Var whose source `Type::Forall` carries a class constraint. Fixture pinned by `print_with_class_method_arg_does_not_misalign_mono_cursor` in crates/ail/tests/show_print_e2e.rs.")
+    (type (fn-type (params) (ret (con Unit)) (effects IO)))
+    (params)
+    (body (app print (app eq 1 2)))))