fix(ir): exhaustive named-const array dims (0083) + nested slice-literal coercion (0085)

Makes the F0.4 fixes exhaustive across every resolution / nesting path.

0083 — named-const array dimension, stateless paths. Attempt 1 fixed the
stateful resolver (direct local decls, struct fields, params, returns) but the
binding-free registration-time resolver (`type_bridge`, used for type aliases
`Arr :: [N]T` and inline union/enum field types) still resolved a named dim with
a silent `else 0`, so `Arr :: [N]s64; a : Arr` and `union { a: [N]s64 }` were
still miscompiled (garbage / bus error). Thread the module-global const table
(`ProgramIndex.module_const_map`) into `type_bridge` alongside the alias map, so
`StatelessInner.resolveArrayLen` resolves a named module-const dim to the same
length everywhere. The remaining unresolvable case (a computed/comptime dim on
the binding-free path, which the stateful path hard-errors) now bails LOUDLY
instead of fabricating a 0 length.

0085 — nested slice-literal elements. `lowerArrayLiteral` lowered each element
with the element type as target but appended the raw value. A nested `.[...]`
element at a slice element type (`[][]s64`) still lowers to an aggregate array
`[N]T`, so the outer aggregate held raw arrays where slice {ptr,len} headers
were expected — indexing the inner slice read a garbage pointer and segfaulted.
After lowering each element, coerce a same-element array to the slice element
type via the existing `array_to_slice` op. The coercion recurses with the
nesting, so `[][]T` and deeper materialize at every level — local-bound AND
direct-call-argument forms.

Regressions (fail-before/pass-after demonstrated on the pre-fix compiler):
  examples/0140-types-named-const-array-dim.sx — extended with type-alias,
    nested [N][M]T, and union-field named dims (s64 / string / struct elems)
  examples/0142-types-nested-slice-literal-elements.sx — [][]s64 + [][]string,
    local-bound vs direct-arg
  src/ir/type_bridge.test.zig — named-const dim resolves to literal length

Gate: zig build, zig build test, bash tests/run_examples.sh (388 passed).
Issues 0083 and 0085 marked RESOLVED.

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

@@ -9,9 +9,22 @@
 > type). The stateful `Lowering.resolveArrayLen` evaluates the dimension as a
 > compile-time integer across the comptime-constant, generic-value, and
 > module-global const tables, and emits a diagnostic (no fabricated length) when
-> it isn't one. Files: `src/ir/type_resolver.zig`, `src/ir/lower.zig`,
+> it isn't one.
+>
+> **Exhaustive follow-up (attempt 2).** The first fix covered every *stateful*
+> resolution path (direct local decls, struct fields, function params/returns),
+> but the *stateless* registration-time resolver (`type_bridge`, used for type
+> aliases `Arr :: [N]T` and inline union/enum field types) still resolved the
+> named dim with a silent `else 0` — so `Arr :: [N]s64; a : Arr` and
+> `union { a: [N]s64 }` were still miscompiled. Fix: the module-global const
+> table (`ProgramIndex.module_const_map`) is now threaded into `type_bridge`
+> alongside the alias map, so `StatelessInner.resolveArrayLen` resolves a named
+> module-const dim to the same length everywhere. The remaining unresolvable case
+> (a computed/comptime dimension on the binding-free path) bails LOUDLY instead of
+> fabricating a 0 length. Files: `src/ir/type_resolver.zig`, `src/ir/lower.zig`,
 > `src/ir/type_bridge.zig`. Regression: `examples/0140-types-named-const-array-dim.sx`
-> (s64 + string + struct element types).
+> (direct + type-alias + nested `[N][M]T` + union-field dims, s64 / string /
+> struct element types).
 
 ## Symptom
 A fixed array whose dimension is a module-global integer constant (`N :: 16;

issues/0085-nested-slice-literal-elements-not-coerced.md

@@ -0,0 +1,55 @@
+# 0085 — nested slice literal elements are stored as raw arrays
+
+> **RESOLVED.** Root cause: `Lowering.lowerArrayLiteral` lowered each element with
+> the element type as `target_type` but appended the returned value directly. For
+> a nested `.[...]` element whose expected element type is a slice (`[]T`), the
+> inner literal still lowers to an aggregate ARRAY `[N]T` — so the outer aggregate
+> (typed array-of-`[]T`) held raw arrays where slice {ptr,len} headers were
+> expected; indexing the inner slice read a garbage pointer and segfaulted. Fix:
+> after lowering each element, when the element type is a slice and the lowered
+> value is a same-element array, coerce it via the existing `array_to_slice` op
+> (materialize backing storage + build the header) — identical to the whole-
+> literal coercion the var-decl / call-arg paths already run. The coercion
+> recurses with the nesting, so `[][]T` and deeper materialize at every level.
+> Files: `src/ir/lower.zig` (`lowerArrayLiteral`). Regression:
+> `examples/0142-types-nested-slice-literal-elements.sx` (`[][]s64` + `[][]string`,
+> local-bound AND direct-call-argument forms).
+
+## Symptom
+Nested array/slice literals such as `.[.[1, 2], .[3, 4]]` miscompile when the
+expected element type is a slice (`[][]s64`). Observed: both the local-bound and
+direct-call forms segfault while indexing the inner slice. Expected: both forms
+materialize each inner `[N]T` literal as a `[]T` slice and print the same value.
+
+## Reproduction
+```sx
+#import "modules/std.sx";
+
+sum_nested :: (xss: [][]s64) -> s64 {
+    return xss[0][1] + xss[1][0];
+}
+
+main :: () {
+    local : [][]s64 = .[.[1, 2], .[3, 4]];
+    print("local={}\n", sum_nested(local));
+    print("direct={}\n", sum_nested(.[.[1, 2], .[3, 4]]));
+}
+```
+Observed on `flow/sx-foundation/F0.4`: segfault at address `0x9` before either
+line prints. Expected output:
+```text
+local=5
+direct=5
+```
+
+## Investigation prompt
+Fix nested slice literal materialization. The likely area is
+`src/ir/lower.zig` in `Lowering.lowerArrayLiteral`: the outer literal can know
+its expected element type is `[]T`, and the loop sets `self.target_type =
+elem_ty` while lowering each inner literal, but it appends the returned value
+directly. For an inner `.[...]`, that returned value is still an array aggregate
+`[N]T`, not the target `[]T` slice. Add per-element coercion/materialization
+after lowering each element, using the element source type and expected
+`elem_ty` (the existing `array_to_slice` coercion should be reused). Verify the
+repro prints `local=5` and `direct=5`, then run `zig build && zig build test &&
+bash tests/run_examples.sh`.