feat(check): harden the ownership analysis for universal activation (0063)

The strict linearity check (use-after-consume / consume-while-borrowed,
linearity.rs) runs today only on the ~45 of 258 all-explicit-mode fns;
its activation gate skips any fn with a bare/Implicit param. Deleting
ParamMode::Implicit (#55) would turn it on universally and surface ~21%
false positives in two classes. This closes both, making the core
ownership analysis sharp across the whole codebase for the first time —
the precondition for #55. Diagnostic-only: no schema, no hash, no
codegen change; the two existing diagnostic codes simply fire on a
smaller, more correct set.

Fix 1 — value-type exemption. A new is_value_type predicate
(ailang-core::primitives) names the unboxed set {Int,Bool,Float,Unit};
BinderState gains an is_value flag seeded from the binder's locally
available type (param signatures, ctor field types for pattern binders,
lam typed-params), and use_var short-circuits the Consume arm for it. A
value type has no refcount and is never consumed, so multi-read is
always legal.

  Str is deliberately NOT in the value set, though is_primitive_name
  includes it: drop.rs:490-492 lowers only Int/Bool/Float/Unit to
  non-ptr; Str is a ptr, RC-dec'd, so a multi-consume of Str without
  clone is a real use-after-free. is_value_type is the Str-excluding
  subset of is_primitive_name, pinned by a unit test. is_heap_type and
  the over-strict-mode lint are left untouched (separate concern).

Fix 2 — application is a borrow. Term::App walks its callee in
Position::Borrow (was Consume). Applying a function value reads it; it
stays live for further applications. Global fn-refs are untracked
(no-op); a tracked function-typed binder (a HOF param) is no longer
consumed by application. This fixes both the own-f-param
use-after-consume and the borrow-f-param consume-while-borrowed in the
recursion-passing HOF shape (map_int f t). Passing a function value as
an arg is unchanged — it follows the callee param_modes.

Scope decision: value-typed let-binders stay conservatively tracked as
heap (their type is inferred, not annotated, and the linearity walk
does not re-run inference). This is soundness-safe — over-strict, never
unsound — and not a measured corpus shape; lifting it would need a full
binder->type table out of the type-checker.

Verification: all three false-positive classes reproduced today against
explicit-mode fns and shipped as RED->GREEN fixtures
(examples/fp_{value,hof,map}.ail); examples/real_consume.ail stays RED
(heap double-consume still fires) to prove the exemption is type-gated.
715 workspace tests green; bench/check.py 0/34 and bench/compile_check.py
0/24 regressed. merge_states carries is_value so the flag survives
branch merges. RED-first verified per task.

closes #56

crates/ailang-check/src/linearity.rs

@@ -27,7 +27,11 @@
 //!   binder.
 //!
 //! Position propagation:
-//! - `Term::App.callee` — Consume (the value is called once).
+//! - `Term::App.callee` — Borrow (applying a function value reads it;
+//!   the value stays live for further applications and is dropped at
+//!   scope close). A global fn-ref callee is untracked, so this is a
+//!   no-op there; a tracked function-typed binder is not consumed by
+//!   application.
 //! - `Term::App.args[i]` — Borrow if the callee is a `Var` whose
 //!   resolved type is a `Type::Fn` with `param_modes[i] == Borrow`;
 //!   otherwise Consume (Own / Implicit / unknown all default to
@@ -163,6 +167,13 @@ fn is_heap_type(t: &Type) -> bool {
     }
 }
 
+/// `true` iff `t` is an unboxed value type (`Int`/`Bool`/`Float`/`Unit`).
+/// The `Str`-excluding counterpart of `is_heap_type`'s primitive check —
+/// see `ailang_core::primitives::is_value_type`.
+fn type_is_value(t: &Type) -> bool {
+    matches!(t, Type::Con { name, .. } if ailang_core::primitives::is_value_type(name))
+}
+
 /// Position in which a [`Term::Var`] is being used. See module-level
 /// docs for the propagation rules.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -189,6 +200,12 @@ struct BinderState {
     /// the borrow ends. Consume while `> 0` triggers
     /// `consume-while-borrowed`.
     borrow_count: u32,
+    /// `true` if this binder has an unboxed value type
+    /// (`Int`/`Bool`/`Float`/`Unit`). A value type has no refcount and
+    /// is never consumed, so `use_var` skips all consume bookkeeping
+    /// for it. Invariant per binder; set at the introduction site
+    /// (param / pattern / lam) where the type is locally available.
+    is_value: bool,
 }
 
 /// top-level entry. Walks every fn in `m` and emits
@@ -352,19 +369,22 @@ fn check_fn(
         globals,
         diags,
         def_name: &f.name,
+        ctors,
         binders: HashMap::new(),
     };
 
     // Install fn parameters as binders, with initial `borrow_count = 1`
     // for `Borrow` params (the caller's outer borrow stays live for the
-    // body's whole duration) and `0` for `Own` params.
+    // body's whole duration) and `0` for `Own` params. A value-type
-    for (name, mode) in f.params.iter().zip(param_modes.iter()) {
+    // param starts `is_value = true` and is exempt from consume-tracking.
+    for (i, (name, mode)) in f.params.iter().zip(param_modes.iter()).enumerate() {
         let initial = BinderState {
             consumed: false,
             borrow_count: match mode {
                 ParamMode::Borrow => 1,
                 ParamMode::Own | ParamMode::Implicit => 0,
             },
+            is_value: param_tys.get(i).map(type_is_value).unwrap_or(false),
         };
         checker.binders.insert(name.clone(), initial);
     }
@@ -414,6 +434,11 @@ struct Checker<'a> {
     /// Name of the fn currently being checked (becomes
     /// [`Diagnostic::def`]).
     def_name: &'a str,
+    /// ctor name → field types. Used to type pattern binders so a
+    /// value-typed sub-binder (`Cons(h, t)` with `h: Int`) is exempted
+    /// from consume-tracking. Mirrors the `ctors` map built in
+    /// `check_module_with_visible`.
+    ctors: &'a HashMap<String, Vec<Type>>,
     /// Live binder state, keyed by name. Modified in place; lexical
     /// scoping is restored by [`Checker::with_binder`].
     binders: HashMap<String, BinderState>,
@@ -428,9 +453,16 @@ impl<'a> Checker<'a> {
             Term::Lit { .. } => {}
             Term::Var { name } => self.use_var(name, pos),
             Term::App { callee, args, .. } => {
-                // The callee itself is consumed (it's "the function value");
+                // Applying a function value READS it (a borrow): the value
-                // for var-callees this is typically a global fn ref.
+                // stays live for further applications and is dropped at
-                self.walk(callee, Position::Consume);
+                // scope close like any other binder. For a global fn-ref
+                // callee this is a no-op (globals are untracked, so
+                // `use_var` returns early either way); for a tracked
+                // function-typed binder (a HOF param) it stops application
+                // from consuming the binder. The `consumed` check still
+                // runs in Borrow position, so applying an already-consumed
+                // function value still fires use-after-consume.
+                self.walk(callee, Position::Borrow);
 
                 // Determine arg modes from the callee's resolved type.
                 let arg_modes = self.callee_arg_modes(callee, args.len());
@@ -538,17 +570,22 @@ impl<'a> Checker<'a> {
                     self.walk(a, Position::Borrow);
                 }
             }
-            Term::Lam { params, body, .. } => {
+            Term::Lam { params, param_tys, body, .. } => {
                 // Lam captures cross the linearity boundary: any free
                 // var of the body is implicitly consumed by closure
                 // construction (we don't yet model captured-borrow
                 // discipline; that is 18c.3 territory). For 18c.2 we
                 // walk the body with the lam's own params as fresh
-                // binders.
+                // binders; a value-typed lam param is exempt from
+                // consume-tracking.
                 let mut saved_for_params: HashMap<String, Option<BinderState>> = HashMap::new();
-                for p in params {
+                for (i, p) in params.iter().enumerate() {
                     saved_for_params.insert(p.clone(), self.binders.remove(p));
-                    self.binders.insert(p.clone(), BinderState::default());
+                    let st = BinderState {
+                        is_value: param_tys.get(i).map(type_is_value).unwrap_or(false),
+                        ..BinderState::default()
+                    };
+                    self.binders.insert(p.clone(), st);
                 }
                 self.walk(body, Position::Consume);
                 for p in params {
@@ -637,10 +674,16 @@ impl<'a> Checker<'a> {
     /// borrow vs. consume, which is 18c.3 work).
     fn walk_arm(&mut self, arm: &Arm, pos: Position) {
         let names = collect_pattern_binders(&arm.pat);
+        let mut value_names: Vec<String> = Vec::new();
+        collect_value_pattern_binders(&arm.pat, None, self.ctors, &mut value_names);
         let mut saved: HashMap<String, Option<BinderState>> = HashMap::new();
         for n in &names {
             saved.insert(n.clone(), self.binders.remove(n));
-            self.binders.insert(n.clone(), BinderState::default());
+            let st = BinderState {
+                is_value: value_names.contains(n),
+                ..BinderState::default()
+            };
+            self.binders.insert(n.clone(), st);
         }
         self.walk(&arm.body, pos);
         for n in &names {
@@ -681,6 +724,11 @@ impl<'a> Checker<'a> {
                 // sibling args, and for the per-fn-param initial value.
             }
             Position::Consume => {
+                // A value type has no refcount and is never consumed;
+                // multi-use in any position is legal.
+                if state.is_value {
+                    return;
+                }
                 if state.borrow_count > 0 {
                     self.diags
                         .push(make_consume_while_borrowed(self.def_name, name));
@@ -774,6 +822,36 @@ fn collect_pattern_binders(p: &Pattern) -> Vec<String> {
     }
 }
 
+/// Collect the names of pattern binders that have an unboxed value
+/// type, by walking the pattern alongside the ctor field types.
+/// Mirrors `pattern_has_consumed_heap_binder_at`'s descent: a
+/// `Pattern::Var` directly under a ctor field of value type is added;
+/// a top-level `Pattern::Var` (whole-scrutinee binder, `declared_ty ==
+/// None`) is conservatively treated as heap and never added.
+fn collect_value_pattern_binders(
+    pat: &Pattern,
+    declared_ty: Option<&Type>,
+    ctors: &HashMap<String, Vec<Type>>,
+    out: &mut Vec<String>,
+) {
+    match pat {
+        Pattern::Wild | Pattern::Lit { .. } => {}
+        Pattern::Var { name } => {
+            if let Some(t) = declared_ty {
+                if type_is_value(t) {
+                    out.push(name.clone());
+                }
+            }
+        }
+        Pattern::Ctor { ctor, fields } => {
+            let field_tys: &[Type] = ctors.get(ctor).map(|v| v.as_slice()).unwrap_or(&[]);
+            for (i, f) in fields.iter().enumerate() {
+                collect_value_pattern_binders(f, field_tys.get(i), ctors, out);
+            }
+        }
+    }
+}
+
 /// Conservative merge of two branch states: a binder is consumed in
 /// the merged state iff it was consumed in either branch; borrow_count
 /// becomes the max of the two. Names present only in one map are
@@ -783,6 +861,9 @@ fn merge_states(into: &mut HashMap<String, BinderState>, other: &HashMap<String,
         let entry = into.entry(name.clone()).or_default();
         entry.consumed = entry.consumed || s.consumed;
         entry.borrow_count = entry.borrow_count.max(s.borrow_count);
+        // is_value is invariant per binder; the OR recovers it when the
+        // binder reached `into` via a fresh `or_default()`.
+        entry.is_value = entry.is_value || s.is_value;
     }
 }
 
@@ -1314,6 +1395,161 @@ mod tests {
         })
     }
 
+    /// A fn with one function-typed param `p0 : (mode (Int -> Int))`,
+    /// returning Int. Used to exercise HOF application linearity.
+    fn fn_with_fn_param(name: &str, mode: ParamMode, body: Term) -> Def {
+        Def::Fn(FnDef {
+            name: name.into(),
+            ty: Type::Fn {
+                params: vec![Type::Fn {
+                    params: vec![Type::int()],
+                    param_modes: vec![ParamMode::Own],
+                    ret: Box::new(Type::int()),
+                    ret_mode: ParamMode::Own,
+                    effects: vec![],
+                }],
+                param_modes: vec![mode],
+                ret: Box::new(Type::int()),
+                ret_mode: ParamMode::Implicit,
+                effects: vec![],
+            },
+            params: vec!["p0".into()],
+            body,
+            suppress: vec![],
+            doc: None,
+            export: None,
+        })
+    }
+
+    /// Applying a function param more than once is a borrow each time,
+    /// not a consume: `(app p0 (app p0 0))` must NOT fire
+    /// use-after-consume. (Today the App callee is walked Consume, so
+    /// the first application consumes `p0` and the second fires
+    /// use-after-consume — this test is RED until Fix 2.)
+    #[test]
+    fn own_fn_param_applied_twice_is_clean() {
+        let body = Term::App {
+            callee: Box::new(Term::Var { name: "p0".into() }),
+            args: vec![Term::App {
+                callee: Box::new(Term::Var { name: "p0".into() }),
+                args: vec![Term::Lit { lit: Literal::Int { value: 0 } }],
+                tail: false,
+            }],
+            tail: false,
+        };
+        let m = Module {
+            schema: ailang_core::SCHEMA.into(),
+            name: "t".into(),
+            kernel: false,
+            imports: vec![],
+            defs: vec![fn_with_fn_param("f", ParamMode::Own, body)],
+        };
+        let diags = check_module(&m);
+        assert!(
+            !diags.iter().any(|d| d.code == "use-after-consume"),
+            "applying a function param is a borrow, not a consume; got {diags:?}"
+        );
+    }
+
+    /// A fn with one `(own (con Int))` value-type param `p0`, returning
+    /// Int. Used to exercise the value-type exemption.
+    fn fn_with_int_own(name: &str, body: Term) -> Def {
+        Def::Fn(FnDef {
+            name: name.into(),
+            ty: Type::Fn {
+                params: vec![Type::Con { name: "Int".into(), args: vec![] }],
+                param_modes: vec![ParamMode::Own],
+                ret: Box::new(Type::int()),
+                ret_mode: ParamMode::Implicit,
+                effects: vec![],
+            },
+            params: vec!["p0".into()],
+            body,
+            suppress: vec![],
+            doc: None,
+            export: None,
+        })
+    }
+
+    /// A value-type param read in two consume positions
+    /// (`(seq p0 p0)`) must NOT fire use-after-consume: an `Int` has no
+    /// refcount and is never consumed. RED until Fix 1.
+    #[test]
+    fn value_param_multi_read_is_clean() {
+        let body = Term::Seq {
+            lhs: Box::new(Term::Var { name: "p0".into() }),
+            rhs: Box::new(Term::Var { name: "p0".into() }),
+        };
+        let m = Module {
+            schema: ailang_core::SCHEMA.into(),
+            name: "t".into(),
+            kernel: false,
+            imports: vec![],
+            defs: vec![fn_with_int_own("f", body)],
+        };
+        let diags = check_module(&m);
+        assert!(
+            !diags.iter().any(|d| d.code == "use-after-consume"),
+            "a value-type param is never consumed; multi-read is legal; got {diags:?}"
+        );
+    }
+
+    /// Type-gating guard: a HEAP param (`List`) consumed twice in a ctor
+    /// (`(term-ctor Pair Pair p0 p0)`) MUST still fire use-after-consume
+    /// after the fix — the exemption is value-type-only, not blanket.
+    /// (Green today and after the fix; a regression guard, not RED-first.)
+    #[test]
+    fn heap_param_multi_consume_still_errors() {
+        let body = Term::Ctor {
+            type_name: "Pair".into(),
+            ctor: "Pair".into(),
+            args: vec![
+                Term::Var { name: "p0".into() },
+                Term::Var { name: "p0".into() },
+            ],
+        };
+        let m = Module {
+            schema: ailang_core::SCHEMA.into(),
+            name: "t".into(),
+            kernel: false,
+            imports: vec![],
+            defs: vec![fn_with_modes("f", vec![ParamMode::Own], body)],
+        };
+        let diags = check_module(&m);
+        assert!(
+            diags.iter().any(|d| d.code == "use-after-consume"),
+            "a heap param consumed twice must still error; got {diags:?}"
+        );
+    }
+
+    /// A borrow function param applied AND passed (the recursive-HOF
+    /// shape `map_int`) must be clean: application is a borrow, and the
+    /// param starts borrowed, so neither use-after-consume nor
+    /// consume-while-borrowed should fire. Covered by Fix 2 (App
+    /// borrow); this asserts the borrow-param variant. RED until Fix 2.
+    #[test]
+    fn borrow_fn_param_applied_is_clean() {
+        let body = Term::App {
+            callee: Box::new(Term::Var { name: "p0".into() }),
+            args: vec![Term::Lit { lit: Literal::Int { value: 0 } }],
+            tail: false,
+        };
+        let m = Module {
+            schema: ailang_core::SCHEMA.into(),
+            name: "t".into(),
+            kernel: false,
+            imports: vec![],
+            defs: vec![fn_with_fn_param("f", ParamMode::Borrow, body)],
+        };
+        let diags = check_module(&m);
+        assert!(
+            !diags.iter().any(|d| {
+                d.code == "use-after-consume" || d.code == "consume-while-borrowed"
+            }),
+            "applying a borrow function param is a clean read; got {diags:?}"
+        );
+    }
+
     /// All-Implicit fn → check is skipped, no diagnostics, even if the
     /// body would trigger a use-after-consume under explicit modes.
     #[test]

crates/ailang-check/tests/workspace.rs

@@ -719,6 +719,39 @@ fn borrow_own_demo_is_linearity_clean() {
     );
 }
 
+/// #56 Fix 1+2: under universal activation the linearity analysis must
+/// not false-fire on value-type params or on applied function params.
+/// These three fixtures use explicit-mode signatures (so the analysis
+/// is active today) and were RED before the hardening (docs/specs/0063).
+#[test]
+fn harden_ownership_false_positives_are_clean() {
+    for name in ["fp_value", "fp_hof", "fp_map"] {
+        let entry = examples_dir().join(format!("{name}.ail"));
+        let ws = load_workspace(&entry).unwrap_or_else(|e| panic!("load {name}: {e:?}"));
+        let diags = check_workspace(&ws);
+        let lin: Vec<&ailang_check::Diagnostic> = diags
+            .iter()
+            .filter(|d| d.code == "use-after-consume" || d.code == "consume-while-borrowed")
+            .collect();
+        assert!(lin.is_empty(), "{name} must be linearity-clean; got: {lin:#?}");
+    }
+}
+
+/// #56 type-gating: the exemption is value-type-only. A heap param
+/// consumed twice (`real_consume.dup`, `(term-ctor Pair Pair b b)`) MUST
+/// still fire use-after-consume — proving the fix did not blanket-silence
+/// genuine multi-consume.
+#[test]
+fn harden_ownership_heap_double_consume_still_errors() {
+    let entry = examples_dir().join("real_consume.ail");
+    let ws = load_workspace(&entry).expect("load real_consume");
+    let diags = check_workspace(&ws);
+    assert!(
+        diags.iter().any(|d| d.code == "use-after-consume"),
+        "real_consume.dup must still fire use-after-consume; got: {diags:#?}"
+    );
+}
+
 /// RED for fieldtest finding B1 (docs/specs/0058): reading a
 /// `borrow (RawBuf a)` *parameter* through a borrow-receiver op
 /// (`RawBuf.get` / `RawBuf.size`) must check clean. Both ops are

crates/ailang-core/src/primitives.rs

@@ -17,6 +17,18 @@ pub fn is_primitive_name(name: &str) -> bool {
     matches!(name, "Int" | "Bool" | "Str" | "Unit" | "Float")
 }
 
+/// Returns `true` iff `name` is an **unboxed value type** — no RC, no
+/// heap slab, copied by value. This is the `Str`-excluding subset of
+/// [`is_primitive_name`]: `Str` is a primitive zero-arity ctor but is
+/// heap-allocated (`ptr`, RC-`dec`'d — codegen `drop.rs:490-492` lowers
+/// only `Int`/`Bool`/`Float`/`Unit` to non-`ptr`). Used by the
+/// linearity analysis to exempt value-type binders from
+/// consume-tracking: a value type is never consumed, so multi-use is
+/// always legal.
+pub fn is_value_type(name: &str) -> bool {
+    matches!(name, "Int" | "Bool" | "Float" | "Unit")
+}
+
 /// Returns the static-lifetime surface name iff `name` is a
 /// primitive. Used by the mono pass to embed the human-readable
 /// form in monomorphised symbol names; the static lifetime is what
@@ -60,4 +72,24 @@ mod tests {
             "Float surface name must be \"Float\""
         );
     }
+
+    /// `is_value_type` is the unboxed/no-RC subset of the primitives:
+    /// it agrees with `is_primitive_name` on every name EXCEPT `Str`,
+    /// which is a primitive zero-arity ctor but is heap-allocated
+    /// (`ptr`, RC'd) — see drop.rs:490-492.
+    #[test]
+    fn value_type_is_primitive_minus_str() {
+        for name in ["Int", "Bool", "Float", "Unit"] {
+            assert!(is_value_type(name), "{name} must be a value type");
+            assert!(is_primitive_name(name), "{name} must be a primitive");
+        }
+        // The sole divergence: Str is a primitive but NOT a value type.
+        assert!(!is_value_type("Str"), "Str is heap-allocated, not a value type");
+        assert!(is_primitive_name("Str"), "Str is still a primitive zero-arity ctor");
+        // Non-primitives are neither.
+        for name in ["List", "Foo", ""] {
+            assert!(!is_value_type(name));
+            assert!(!is_primitive_name(name));
+        }
+    }
 }

examples/fp_hof.ail

@@ -0,0 +1,12 @@
+(module fp_hof
+  (fn apply_thrice
+    (doc "apply a function param three times")
+    (type (fn-type
+            (params (own (fn-type (params (own (con Int))) (ret (own (con Int))))) (own (con Int)))
+            (ret (own (con Int)))))
+    (params f x)
+    (body (app f (app f (app f x)))))
+  (fn main
+    (type (fn-type (params) (ret (own (con Unit))) (effects IO)))
+    (params)
+    (body (app print (app apply_thrice (lam (params (typed y (con Int))) (ret (con Int)) (body (app + y 1))) 0)))))

examples/fp_map.ail

@@ -0,0 +1,14 @@
+(module fp_map
+  (data IntList
+    (doc "boxed list")
+    (ctor Nil)
+    (ctor Cons (con Int) (con IntList)))
+  (fn map_int
+    (doc "recursive HOF: f applied AND passed to the recursive call")
+    (type (fn-type
+            (params (borrow (fn-type (params (own (con Int))) (ret (own (con Int))))) (own (con IntList)))
+            (ret (own (con IntList)))))
+    (params f xs)
+    (body (match xs
+      (case (pat-ctor Nil) (term-ctor IntList Nil))
+      (case (pat-ctor Cons h t) (term-ctor IntList Cons (app f h) (app map_int f t)))))))

examples/fp_value.ail

@@ -0,0 +1,10 @@
+(module fp_value
+  (fn sum_explicit
+    (doc "value-type param read multiple times")
+    (type (fn-type (params (own (con Int))) (ret (own (con Int)))))
+    (params n)
+    (body (if (app eq n 0) 0 (app + n (app sum_explicit (app - n 1))))))
+  (fn main
+    (type (fn-type (params) (ret (own (con Unit))) (effects IO)))
+    (params)
+    (body (app print (app sum_explicit 10)))))

examples/real_consume.ail

@@ -0,0 +1,12 @@
+(module real_consume
+  (data Box
+    (doc "heap cell")
+    (ctor Box (con Int)))
+  (data Pair
+    (doc "two boxes")
+    (ctor Pair (con Box) (con Box)))
+  (fn dup
+    (doc "MUST STAY an error: a heap param consumed twice without clone")
+    (type (fn-type (params (own (con Box))) (ret (own (con Pair)))))
+    (params b)
+    (body (term-ctor Pair Pair b b))))