fix(ir): value-param type functions + range-checked dim/lane fold (0083, 0087)

Two remaining siblings in F0.4's comptime-int path.

1. Type-returning function with a value param used as a TYPE annotation
   (`b : Make(N, s64)` where `Make :: ($K: u32, $T: Type) -> Type`):
   - `isValueParamPosition` (semantic_diagnostics) now also skips a value
     param of a `fn_ast_map` type-returning function, so `N` is not walked
     as the type name "N" ("unknown type 'N'").
   - `resolveParameterizedWithBindings` routes a type-returning-function
     name to `instantiateTypeFunction` (the `.call` path already did).
   - `instantiateTypeFunction` resolves a general return-type expression
     (`return [K]T`) with bindings active — not just struct/union returns.
   `Make(N, s64)`, `Make(M + 1, s64)`, `Make(3, s64)` all resolve to one
   `[3]s64`.

2. Oversized dim/lane fold panicked the compiler (0087): an array dim /
   Vector lane folded to a valid i64 (5e9) then narrowed to u32 with an
   unchecked `@intCast`. New single gate `program_index.foldDimU32` folds
   via `evalConstIntExpr` then range-checks `[min, maxInt(u32)]`; the three
   narrowing sites (resolveArrayLen stateful + stateless, resolveVectorLane)
   all route through it and emit a clean diagnostic + halt instead of
   panicking. Value-param args stay i64 until used as a dim/lane, where the
   same gate checks them.

Regressions: examples/0208 (value-param type function), examples/1130
(oversized array dim clean halt), examples/1503 (oversized Vector lane
clean halt). Marks issue 0087 RESOLVED.

Gate: zig build, zig build test, bash tests/run_examples.sh — 398 passed,
0 failed, 0 timed out.

examples/0208-generics-value-param-type-function.sx

@@ -0,0 +1,32 @@
+// A type-RETURNING function with a value parameter (`$K: u32`) used as a TYPE
+// annotation: `b : Make(N, s64)` where `Make :: ($K, $T) -> Type { return [K]T; }`.
+// A named-const value arg (`Make(N, s64)`), a const-expression value arg
+// (`Make(M + 1, s64)`), and the literal form (`Make(3, s64)`) all instantiate to
+// the SAME type — the array copy `b : Make(3, s64) = a` type-checks only because
+// the three spellings name one `[3]s64`.
+//
+// Regression (issue 0083 / F0.4 attempt 6): the unknown-type checker walked the
+// value-param position as a type name ("unknown type 'N'"), and the
+// parameterized-type-annotation path never routed to `instantiateTypeFunction`,
+// nor did that binder resolve a non-struct/union return shape (`return [K]T`).
+// The value arg now folds through the shared const-int evaluator and the type
+// function resolves its general return-type expression with bindings active.
+#import "modules/std.sx";
+
+N :: 3;
+M :: 2;
+
+Make :: ($K: u32, $T: Type) -> Type { return [K]T; }
+
+main :: () {
+    a : Make(N, s64) = ---;          // named-const value param
+    a[0] = 10; a[1] = 20; a[2] = 30;
+    print("named: len={} a0={} a2={}\n", a.len, a[0], a[2]);
+
+    e : Make(M + 1, s64) = ---;      // const-expr value param (M + 1 == 3)
+    e[0] = 1; e[2] = 9;
+    print("expr: len={} e2={}\n", e.len, e[2]);
+
+    b : Make(3, s64) = a;            // same instantiation → array copy type-checks
+    print("copy: len={} b2={}\n", b.len, b[2]);
+}

examples/1130-diagnostics-array-dim-oversized-u32.sx

@@ -0,0 +1,15 @@
+// An array dimension that folds to a valid compile-time integer but exceeds a
+// `u32` (`[5_000_000_000]s64`) is a hard error — a clean sx diagnostic with a
+// non-zero exit, NOT a compiler panic.
+//
+// Regression (issue 0087 / F0.4 attempt 6): the dimension folded to a valid i64
+// (5e9) and was then narrowed with an unchecked `@intCast` to u32, aborting the
+// COMPILER with "integer does not fit in destination type". Every dim/lane fold
+// now narrows through the single range-checked `program_index.foldDimU32`, which
+// reports an out-of-u32-range dimension as this diagnostic and halts the build.
+#import "modules/std.sx";
+
+main :: () {
+    a : [5000000000]s64 = ---;
+    print("unreachable: {}\n", a.len);
+}

examples/1503-vectors-oversized-lane-not-u32.sx

@@ -0,0 +1,15 @@
+// A `Vector` lane count that folds to a valid compile-time integer but exceeds a
+// `u32` (`Vector(5_000_000_000, f32)`) is a hard error — a clean sx diagnostic
+// with a non-zero exit, NOT a compiler panic.
+//
+// Regression (issue 0087 / F0.4 attempt 6): the lane folded to a valid i64 (5e9)
+// and was then narrowed with an unchecked `@intCast` to u32, aborting the
+// COMPILER with "integer does not fit in destination type". The lane now narrows
+// through the single range-checked `program_index.foldDimU32`, which reports an
+// out-of-u32-range lane as this diagnostic and halts the build.
+#import "modules/std.sx";
+
+main :: () {
+    v : Vector(5000000000, f32) = ---;
+    print("unreachable: {}\n", v.x);
+}

examples/expected/0208-generics-value-param-type-function.exit

@@ -0,0 +1 @@
+0

examples/expected/0208-generics-value-param-type-function.stderr

@@ -0,0 +1 @@
+

examples/expected/0208-generics-value-param-type-function.stdout

@@ -0,0 +1,3 @@
+named: len=3 a0=10 a2=30
+expr: len=3 e2=9
+copy: len=3 b2=30

examples/expected/1130-diagnostics-array-dim-oversized-u32.exit

@@ -0,0 +1 @@
+1

examples/expected/1130-diagnostics-array-dim-oversized-u32.stderr

@@ -0,0 +1,5 @@
+error: array dimension 5000000000 does not fit in u32
+  --> examples/1130-diagnostics-array-dim-oversized-u32.sx:13:10
+   |
+13 |     a : [5000000000]s64 = ---;
+   |          ^^^^^^^^^^

examples/expected/1130-diagnostics-array-dim-oversized-u32.stdout

@@ -0,0 +1 @@
+

examples/expected/1503-vectors-oversized-lane-not-u32.exit

@@ -0,0 +1 @@
+1

examples/expected/1503-vectors-oversized-lane-not-u32.stderr

@@ -0,0 +1,11 @@
+error: Vector lane count 5000000000 does not fit in u32
+  --> examples/1503-vectors-oversized-lane-not-u32.sx:13:16
+   |
+13 |     v : Vector(5000000000, f32) = ---;
+   |                ^^^^^^^^^^
+
+error: field 'x' not found on type 'unresolved'
+  --> examples/1503-vectors-oversized-lane-not-u32.sx:14:32
+   |
+14 |     print("unreachable: {}\n", v.x);
+   |                                ^^^

examples/expected/1503-vectors-oversized-lane-not-u32.stdout

@@ -0,0 +1 @@
+

issues/0083-named-const-array-dimension-miscompiled.md

@@ -103,6 +103,25 @@
 > resolve to the same instantiation as `Vec(3,f32)`),
 > `examples/0610-comptime-inline-for-const-bound.sx` (`inline for 0..M` and
 > `0..(M+1)` unroll).
+>
+> **Value-param type functions + oversized guard (attempt 6).** Two remaining
+> siblings in the comptime-int path. (1) A type-RETURNING function with a value
+> param used as a TYPE annotation (`b : Make(N, s64)` where `Make :: ($K: u32,
+> $T: Type) -> Type { return [K]T; }`) was rejected "unknown type 'N'" because
+> the unknown-type checker walked the value-param position as a type name, AND the
+> parameterized-type-annotation path never routed to `instantiateTypeFunction`
+> (only the `.call` path did), nor did that binder resolve a non-struct/union
+> return shape. Fix: `isValueParamPosition` (semantic_diagnostics.zig) now also
+> skips a value param of a `fn_ast_map` type-returning function (mirroring the
+> binder's value/type classification); `resolveParameterizedWithBindings` routes
+> a type-returning-function name to `instantiateTypeFunction`; and that binder
+> resolves a general return-type expression (`return [K]T`) with bindings active.
+> `Make(N, s64)`, `Make(M + 1, s64)`, and `Make(3, s64)` now resolve to one
+> `[3]s64`. (2) Oversized dim/lane folds (`[5_000_000_000]`) panicked the
+> compiler — fixed under issue 0087 via the shared range-checked
+> `program_index.foldDimU32` gate. Files: `src/ir/semantic_diagnostics.zig`,
+> `src/ir/lower.zig`, `src/ir/program_index.zig`, `src/ir/type_bridge.zig`.
+> Regression: `examples/0208-generics-value-param-type-function.sx`.
 
 ## Symptom
 A fixed array whose dimension is a module-global integer constant (`N :: 16;

issues/0087-oversized-comptime-int-dimension-panics.md

@@ -0,0 +1,64 @@
+# 0087 - oversized compile-time integer in type dimension/lane panics
+
+> **RESOLVED.** Root cause: an array dimension / Vector lane folded to a valid
+> `i64` (e.g. `5_000_000_000`) was then narrowed to `u32` with an unchecked
+> `@intCast` at three sites (`Lowering.resolveArrayLen` lower.zig:11656,
+> `Lowering.resolveVectorLane` lower.zig:11836, `StatelessInner.resolveArrayLen`
+> type_bridge.zig:58), aborting the COMPILER with "integer does not fit in
+> destination type" — the fold was correct, the narrowing was not. Fix: a single
+> range-checked fold-to-u32 gate, `program_index.foldDimU32(node, ctx, min)`,
+> folds via `evalConstIntExpr` then checks `[min, maxInt(u32)]` and returns a
+> tagged `DimU32` (`.ok` / `.not_const` / `.below_min` / `.too_large`). Every
+> dim/lane narrowing now routes through it — no call site does a bare `@intCast`,
+> so an out-of-u32-range dim/lane surfaces a clean diagnostic ("array dimension N
+> does not fit in u32" / "Vector lane count N does not fit in u32") and halts the
+> build (exit 1) instead of panicking. Value-param args stay `i64` until used as
+> a dim/lane, where the same gate checks them. Files: `src/ir/program_index.zig`
+> (`DimU32` + `foldDimU32`), `src/ir/lower.zig`, `src/ir/type_bridge.zig`.
+> Regressions: `examples/1130-diagnostics-array-dim-oversized-u32.sx` (oversized
+> array dim → clean halt) and `examples/1503-vectors-oversized-lane-not-u32.sx`
+> (oversized Vector lane → clean halt).
+
+## Symptom
+An oversized compile-time integer used where the compiler expects a `u32`
+array dimension or Vector lane count panics inside the compiler instead of
+emitting a source diagnostic.
+
+Observed: `@intCast` panics with "integer does not fit in destination type" in
+`Lowering.resolveArrayLen` / `Lowering.resolveVectorLane`.
+
+Expected: compile halts with a normal diagnostic such as "array dimension does
+not fit in u32" / "Vector lane count must fit in u32", and no compiler panic.
+
+## Reproduction
+```sx
+#import "modules/std.sx";
+
+main :: () {
+    a : [5000000000]s64 = ---;
+    print("{}\n", a.len);
+}
+```
+
+Vector lane sibling:
+
+```sx
+#import "modules/std.sx";
+
+main :: () {
+    v : Vector(5000000000, f32) = .[];
+    print("{}\n", v);
+}
+```
+
+## Investigation prompt
+Fix oversized compile-time integer handling for fixed-array dimensions and
+Vector lane counts. Suspected area: `src/ir/lower.zig`
+`Lowering.resolveArrayLen` and `Lowering.resolveVectorLane`, plus the stateless
+adapter in `src/ir/type_bridge.zig` `StatelessInner.resolveArrayLen`. These
+functions fold to `i64` through `program_index.evalConstIntExpr`, then cast to
+`u32` with `@intCast`; values greater than `std.math.maxInt(u32)` panic in the
+compiler. The fix likely needs an explicit range check before every `u32` cast,
+with a diagnostic on the stateful path and null / `.unresolved` propagation on
+the stateless path. Verify both repros exit 1 with source diagnostics and no
+panic, then run `zig build && zig build test && bash tests/run_examples.sh`.

src/ir/lower.zig

@@ -11639,37 +11639,36 @@ pub const Lowering = struct {
 
     /// Fixed-array dimension hook for `TypeResolver.resolveCompound`. A literal
     /// `[16]T` and a named-const `N :: 16; [N]T` must resolve to the SAME length:
-    /// the dimension is a compile-time integer, looked up in the comptime / value
-    /// / module-const tables the stateful lowering owns. A dimension that isn't a
-    /// compile-time integer is a hard error: emit a diagnostic so the driver
-    /// aborts (`hasErrors()`), then return a harmless `0` so body lowering
-    /// finishes without touching the `.unresolved` sentinel (which would `@panic`
-    /// in `sizeOf` mid-lowering, before the diagnostic surfaces). The diagnostic —
-    /// not the returned length — is what guarantees no garbage ships (issue 0083).
+    /// the dimension folds to a compile-time integer (looked up in the comptime /
+    /// value / module-const tables the stateful lowering owns) and is narrowed to
+    /// `u32` through the single range-checked `program_index.foldDimU32` — never a
+    /// bare `@intCast`, so an oversized-but-valid `i64` dim (`[5_000_000_000]`)
+    /// diagnoses instead of panicking the compiler (issue 0087). A dimension that
+    /// isn't a compile-time integer (or doesn't fit a `u32`) is a hard error:
+    /// emit a diagnostic so the driver aborts (`hasErrors()`), then return a
+    /// harmless `0` so body lowering finishes without touching the `.unresolved`
+    /// sentinel (which would `@panic` in `sizeOf` mid-lowering, before the
+    /// diagnostic surfaces). The diagnostic — not the returned length — is what
+    /// guarantees no garbage ships (issue 0083).
     pub fn resolveArrayLen(self: *Lowering, len_node: *const Node) ?u32 {
-        if (self.comptimeArrayDim(len_node)) |n| {
-            if (n < 0) {
+        switch (program_index_mod.foldDimU32(len_node, self, 0)) {
+            .ok => |n| return n,
+            .below_min => |v| {
                 if (self.diagnostics) |d|
-                    d.addFmt(.err, len_node.span, "array dimension must be non-negative, got {}", .{n});
+                    d.addFmt(.err, len_node.span, "array dimension must be non-negative, got {}", .{v});
                 return 0;
-            }
-            return @intCast(n);
+            },
+            .too_large => |v| {
+                if (self.diagnostics) |d|
+                    d.addFmt(.err, len_node.span, "array dimension {} does not fit in u32", .{v});
+                return 0;
+            },
+            .not_const => {
+                if (self.diagnostics) |d|
+                    d.addFmt(.err, len_node.span, "array dimension must be a compile-time integer constant", .{});
+                return 0;
+            },
         }
-        if (self.diagnostics) |d|
-            d.addFmt(.err, len_node.span, "array dimension must be a compile-time integer constant", .{});
-        return 0;
-    }
-
-    /// Evaluate a fixed-array dimension to a compile-time integer: a literal, a
-    /// name bound to an integer (comptime-constant `OS`/loop cursors, generic
-    /// `$N` value, or module-global const `N :: 16`), or a constant-foldable
-    /// expression over those (`[M + 1]`, `[(M + 1) * 2]`). Delegates the
-    /// expression folding to the shared `program_index.evalConstIntExpr` so this
-    /// body-lowering path and the stateless registration path cannot diverge on
-    /// a dimension's value. Returns null when the dimension isn't a compile-time
-    /// integer.
-    fn comptimeArrayDim(self: *Lowering, node: *const Node) ?i64 {
-        return program_index_mod.evalConstIntExpr(node, self);
     }
 
     /// Leaf-name lookup for the shared dimension evaluator: a name bound to a
@@ -11820,20 +11819,28 @@ pub const Lowering = struct {
     }
 
     /// Resolve a `Vector(N, T)` lane count to a positive compile-time integer
-    /// through the shared `evalConstIntExpr` folder — so a literal (`Vector(4,
-    /// f32)`), a module/generic const (`Vector(N, f32)`), and a const expression
-    /// (`Vector(M + 1, f32)`) all resolve identically. A non-const lane
-    /// (`Vector(get(), f32)`) or a non-positive one emits a clean diagnostic and
-    /// returns null; the caller yields `.unresolved` rather than fabricating a
-    /// `<0 x float>` lane count that crashes LLVM verification.
+    /// through the shared `program_index.foldDimU32` folder (min 1) — so a literal
+    /// (`Vector(4, f32)`), a module/generic const (`Vector(N, f32)`), and a const
+    /// expression (`Vector(M + 1, f32)`) all resolve identically, and the i64→u32
+    /// narrowing is range-checked (an oversized lane diagnoses instead of
+    /// panicking — issue 0087). A non-const lane (`Vector(get(), f32)`) or a
+    /// non-positive one emits a clean diagnostic and returns null; the caller
+    /// yields `.unresolved` rather than fabricating a `<0 x float>` lane count
+    /// that crashes LLVM verification.
     fn resolveVectorLane(self: *Lowering, lane_node: *const Node) ?u32 {
-        const v = program_index_mod.evalConstIntExpr(lane_node, self);
-        if (v == null or v.? < 1) {
-            if (self.diagnostics) |d|
-                d.addFmt(.err, lane_node.span, "Vector lane count must be a positive compile-time integer constant", .{});
-            return null;
+        switch (program_index_mod.foldDimU32(lane_node, self, 1)) {
+            .ok => |n| return n,
+            .too_large => |v| {
+                if (self.diagnostics) |d|
+                    d.addFmt(.err, lane_node.span, "Vector lane count {} does not fit in u32", .{v});
+                return null;
+            },
+            .not_const, .below_min => {
+                if (self.diagnostics) |d|
+                    d.addFmt(.err, lane_node.span, "Vector lane count must be a positive compile-time integer constant", .{});
+                return null;
+            },
         }
-        return @intCast(v.?);
     }
 
     /// Resolve a generic value-param argument (`$N: u32`) to its compile-time
@@ -11909,6 +11916,20 @@ pub const Lowering = struct {
             }
         }
 
+        // User-defined type-returning function used as a TYPE annotation
+        // (`b : Make(N, s64)` where `Make :: ($K: u32, $T: Type) -> Type`). The
+        // `.call`-node path (`resolveTypeCallWithBindings`) already routes here;
+        // a `parameterized_type_expr` must too, or the function name falls through
+        // to the empty-struct stub below and `b.field` / `b.len` fails.
+        const resolved_name = if (self.scope) |scope| (scope.lookupFn(base_name) orelse base_name) else base_name;
+        if (self.program_index.fn_ast_map.get(resolved_name)) |fd| {
+            if (fd.type_params.len > 0) {
+                if (self.instantiateTypeFunction(base_name, base_name, fd, pt.args)) |ty| {
+                    return ty;
+                }
+            }
+        }
+
         // Fallback: register as named type placeholder
         const name_id = table.internString(pt.name);
         return table.intern(.{ .@"struct" = .{ .name = name_id, .fields = &.{} } });
@@ -12141,9 +12162,36 @@ pub const Lowering = struct {
             return self.instantiateTypeUnion(if (has_alias) alias_name else mangled_name, mangled_name, &enum_decl);
         }
 
+        // General case: the body returns a TYPE EXPRESSION that is not an inline
+        // struct/union/enum — `return [K]T`, `Vector(K, T)`, `*T`, an alias, etc.
+        // Resolve it with the value/type bindings active (so `[K]T` folds K to a
+        // compile-time integer). The result is interned structurally, so
+        // `Make(N, s64)`, `Make(3, s64)`, and `Make(M + 1, s64)` all yield the
+        // same TypeId. `.unresolved` means the return wasn't a type expression
+        // (e.g. a value-returning function in a type position) → fall through to
+        // the caller's fallback rather than fabricating a type.
+        if (findReturnTypeExpr(fd.body)) |ret_node| {
+            const ty = self.resolveTypeWithBindings(ret_node);
+            if (ty != .unresolved) return ty;
+        }
+
         return null;
     }
 
+    /// The type expression a type-returning function yields: the value of its
+    /// `return` (block body) or the bare expression (arrow body / `=> [K]T`).
+    /// Used for a non-struct/union return shape, which the struct/union body
+    /// walkers above don't match.
+    fn findReturnTypeExpr(body: *const Node) ?*const Node {
+        if (body.data == .block) {
+            for (body.data.block.stmts) |stmt| {
+                if (stmt.data == .return_stmt) return stmt.data.return_stmt.value;
+            }
+            return null;
+        }
+        return body;
+    }
+
     /// Instantiate a tagged enum from a type function body.
     fn instantiateTypeUnion(self: *Lowering, alias_name: []const u8, mangled_name: []const u8, ed: *const ast.EnumDecl) ?TypeId {
         const table = &self.module.types;

src/ir/program_index.zig

@@ -116,6 +116,37 @@ pub fn evalConstIntExpr(node: *const Node, ctx: anytype) ?i64 {
     };
 }
 
+/// The outcome of folding a comptime-int and narrowing it to a `u32` count
+/// (array dimension / Vector lane / value-param count). `foldDimU32` is the
+/// SINGLE place a folded integer becomes a `u32`, so the i64→u32 narrowing is
+/// range-checked exactly once and no call site does a bare `@intCast` that could
+/// panic the compiler on a valid-but-oversized fold (a literal `5_000_000_000`
+/// is a valid `i64` yet `> maxInt(u32)` — issue 0087). Each call site maps a
+/// non-`.ok` variant onto its own clean diagnostic + `.unresolved` / abort.
+pub const DimU32 = union(enum) {
+    /// Folded to a `u32` in `[min, maxInt(u32)]`.
+    ok: u32,
+    /// Not a compile-time integer (runtime value, unbound name, or overflow).
+    not_const,
+    /// Folded, but below the required minimum (a negative dim, a non-positive lane).
+    below_min: i64,
+    /// Folded, but greater than `maxInt(u32)` — too large for a `u32` count.
+    too_large: i64,
+};
+
+/// Fold `node` to a `u32` count through `evalConstIntExpr`, then range-check
+/// against `[min, maxInt(u32)]`. THE single fold-to-u32 for every array
+/// dimension, Vector lane, and value-param count — routing all of them here
+/// guarantees the narrowing is checked once and can never abort the compiler
+/// (issue 0087). The fold itself stays in `i64`; only this one conversion is the
+/// `u32` gate.
+pub fn foldDimU32(node: *const Node, ctx: anytype, min: u32) DimU32 {
+    const v = evalConstIntExpr(node, ctx) orelse return .not_const;
+    if (v < @as(i64, min)) return .{ .below_min = v };
+    if (v > std.math.maxInt(u32)) return .{ .too_large = v };
+    return .{ .ok = @intCast(v) };
+}
+
 pub const GlobalInfo = struct { id: inst.GlobalId, ty: TypeId };
 
 /// Single lowering access point for declaration-name / import / visibility

src/ir/semantic_diagnostics.zig

@@ -617,12 +617,28 @@ pub const UnknownTypeChecker = struct {
     /// generic `$N: u32` arg), not a type. Such a position must be skipped by
     /// the unknown-type walk: a module-const arg (`Vector(N, f32)`) is a value,
     /// not a type name. `Vector`'s arg 0 is always its lane count; a generic
-    /// struct template's value-param positions come from its declared params.
+    /// struct template's value-param positions come from its declared params; a
+    /// type-RETURNING function (`Make :: ($K: u32, $T: Type) -> Type`) classifies
+    /// each param from its constraint, mirroring `instantiateTypeFunction` — so
+    /// `Make(N, s64)` (N a module const) is not walked as the type name "N".
     fn isValueParamPosition(self: UnknownTypeChecker, base: []const u8, i: usize) bool {
         if (std.mem.eql(u8, base, "Vector")) return i == 0;
         if (self.index.struct_template_map.get(base)) |tmpl| {
             if (i < tmpl.type_params.len) return !tmpl.type_params[i].is_type_param;
         }
+        if (self.index.fn_ast_map.get(base)) |fd| {
+            if (i < fd.type_params.len) {
+                const tp = fd.type_params[i];
+                // A value param is one whose constraint is a non-`Type` type
+                // expr (`$K: u32`); a `$T: Type` (or any non-type-expr
+                // constraint) is a type param — identical rule to the binder.
+                const is_type_param = if (tp.constraint.data == .type_expr)
+                    std.mem.eql(u8, tp.constraint.data.type_expr.name, "Type")
+                else
+                    true;
+                return !is_type_param;
+            }
+        }
         return false;
     }
 

src/ir/type_bridge.zig

@@ -43,19 +43,23 @@ const StatelessInner = struct {
     /// Fixed-array dimension at registration time: a literal `[16]T`, a named
     /// module-global const `N :: 16; [N]T` (typed `N : s64 : 16` too), or a
     /// constant-foldable expression over those (`[M + 1]`, `[(M + 1) * 2]`).
-    /// Folds through the shared `program_index.evalConstIntExpr` — the SAME
-    /// evaluator the stateful body-lowering path uses — so a dimension resolves
-    /// to one length on every registration-time path (aliases, inline union/enum
-    /// fields) and matches the direct form (issue 0083). Returns null when the
-    /// dimension isn't a compile-time integer (a runtime value / non-comptime
-    /// call, or a name not bound to an integer const). Null propagates to
-    /// `resolveCompound`, which yields the `.unresolved` sentinel rather than
-    /// fabricating a 0 length that silently gives a 0-byte array and
-    /// out-of-bounds element access; the registration caller surfaces the
-    /// unresolved alias/type as a clean diagnostic.
+    /// Folds and narrows through the shared `program_index.foldDimU32` (min 0) —
+    /// the SAME range-checked fold-to-u32 the stateful body-lowering path uses —
+    /// so a dimension resolves to one length on every registration-time path
+    /// (aliases, inline union/enum fields) and matches the direct form (issue
+    /// 0083), and an oversized-but-valid `i64` dim returns null instead of
+    /// panicking the `@intCast` (issue 0087). Returns null when the dimension
+    /// isn't a compile-time integer (a runtime value / non-comptime call, or a
+    /// name not bound to an integer const), is negative, or doesn't fit a `u32`.
+    /// Null propagates to `resolveCompound`, which yields the `.unresolved`
+    /// sentinel rather than fabricating a 0 length that silently gives a 0-byte
+    /// array and out-of-bounds element access; the registration caller surfaces
+    /// the unresolved alias/type as a clean diagnostic.
     pub fn resolveArrayLen(self: StatelessInner, len_node: *const Node) ?u32 {
-        const v = program_index_mod.evalConstIntExpr(len_node, self) orelse return null;
-        return if (v >= 0) @intCast(v) else null;
+        return switch (program_index_mod.foldDimU32(len_node, self, 0)) {
+            .ok => |n| n,
+            else => null,
+        };
     }
     /// Leaf-name lookup for the shared dimension evaluator: a name that resolves
     /// to a module-global integer constant → its value. Shares