> **RESOLVED (2026-06-18).** Root cause: `buildPackSliceValue` (`src/ir/lower/pack.zig`)
> built the `$<pack>` `[]Type` slice as `[]Any` (16-byte elements) — a stale mapping
> from before the dedicated `Type` builtin (`.type_value`, 8 bytes) replaced `Type → .any`.
> It stored 8-byte `const_type` words into 16-byte slots, so a `[]Type` reader (8-byte
> stride) read `[t0, pad, t1, …]`. Fix: build the slice/array as `.type_value` (8 bytes).
> Regression test: `examples/0525-packs-pack-as-type-slice-arg.sx`. The stopgap
> `type_name` `.unresolved` guard added in 379ed05 was removed (root cause fixed).
> 700/0 both gates.

# 0143 — A variadic pack passed as `[]Type` across a call is mis-strided (Any-sized backing, Type-sized view)

**Symptom** — When a variadic `..$args` pack is forwarded as a `[]Type` *argument*
to another function, reading `args[i]` yields the **wrong** element: the backing
array is laid out as `[N x Any]` (16-byte `{i64,i64}` slots) but the slice's
element type is `Type`/`type_value` (8 bytes), so an 8-byte-strided index read
lands on `elem0`, then the *padding* of `elem0` (reads as `.unresolved`), then
`elem1`, … — i.e. half-stride reads.

Observed (on the flat-memory comptime VM, which is byte-accurate) vs expected
(legacy interp, whose tagged-`Value` model is stride-agnostic and reads the right
logical element):

```
VM:     [i64 <unresolved> string ]
legacy: [i64 string bool ]
```

The legacy interpreter masks the bug (it indexes a logical sequence of `Value`s,
not bytes). The VM exposes it. This is what makes `examples/0114-types-build-block-convert`
read `arg1: <unresolved>` instead of `arg1: string` once the VM handles `type_name`
(it currently bails on the `.unresolved` read — see the guard added in `comptime_vm.zig`
`type_name`, commit 379ed05 — so under the fallback it falls back; under
`SX_COMPTIME_FLAT_STRICT` it is a hard error).

## Reproduction

```sx
#import "modules/std.sx";

inner :: (args: []Type) -> string {
    s := ""; i : i64 = 0;
    while i < args.len { s = concat(s, type_name(args[i])); s = concat(s, " "); i = i + 1; }
    return s;
}
outer :: (..$args) -> string { return inner($args); }   // <-- pack passed as []Type across a call

R :: #run outer(42, "hi", true);
main :: () { print("[{}]\n", R); }
```

Expected: `[i64 string bool ]`. Actual (VM): `[i64 <unresolved> string ]`.

Note the *direct* use (no cross-call) is fine — `walk :: (..$args) { list := $args; … type_name(list[i]) … }`
reads correctly. Only forwarding the pack as a `[]Type` **argument** mis-strides.

## Root cause (hypothesis)

The pack `$args` is materialised as a `[N x Any]` array (each arg boxed as a
16-byte `Any` — confirmed in the LLVM IR: `array_to_string__AR_3_Any` /
`[3 x { i64, i64 }]`), but when forwarded to a `[]Type` parameter the slice is
typed with element `type_value` (8 bytes). The slice `{ptr,len}` points at the
`[N x Any]` data, so `index_get` with an 8-byte element stride reads garbage.

The fix belongs in **lowering**, not the VM: a pack consumed as `[]Type` must
either (a) materialise a real `[N x Type]` (8-byte) array by extracting each
arg's type tag from its Any box, or (b) keep the slice element type as `Any` and
have `type_name`/reflection read the Any's tag (the VM's `type_name` already
handles an `.any` arg). Option (b) is likely smaller. Whichever: the slice's
element type and its backing array's element size MUST agree.

Suspected area: the pack-expansion / pack-as-slice lowering (search `src/ir/lower/`
for the `..$args` → slice materialisation and the `[]Type` coercion of a value
pack; `pack.zig`).

## Investigation prompt (paste into a fresh session)

> A variadic `..$args` pack forwarded as a `[]Type` argument across a call is
> mis-strided: the backing array is `[N x Any]` (16B slots) but the slice element
> type is `type_value` (8B), so `args[i]` reads at the wrong offset. The legacy
> interp masks it (Value-indexed); the byte-accurate comptime VM exposes it
> (`examples/0114`, and the minimal repro in `issues/0143-…md`). Fix it in
> lowering: make the pack→`[]Type` materialisation agree on element size — either
> build a real `[N x Type]` array (extract each Any's type tag) or type the slice
> `[]Any` and let reflection read the Any tag (`type_name` already handles `.any`).
> Verify: run the repro on the VM (`SX_COMPTIME_FLAT=1 sx run`) and expect
> `[i64 string bool ]`; then `examples/0114` must produce `arg1: string` (not
> `<unresolved>`) and run HANDLED under `SX_COMPTIME_FLAT_STRICT=1` matching legacy.
> Drop the `tid == .unresolved` guard in `comptime_vm.zig` `type_name` once the
> root cause is fixed (it was a stopgap so the VM declines rather than emits
> garbage).

## Status

OPEN. Blocks `examples/0114` from running HANDLED on the comptime VM (Phase 4
legacy-interp retirement). Not a blocker for the other comptime-op ports.
