Pack-fn bodies that index the pack via `args[<int_literal>]`
now resolve to the i-th call-site argument's lowered value
directly, propagating the call arg's concrete type instead
of the boxed `Any` that the `[]Any` slice path returns.
New plumbing in `src/ir/lower.zig`:
- `pack_arg_nodes: ?std.StringHashMap([]const *const Node)` on
Lowering. Maps a pack param name (e.g. "args") to the slice
of call-site arg AST nodes.
- `lowerComptimeCall` populates the map when the variadic
param is heterogeneous (`is_variadic AND is_comptime`, i.e.
the `..$args` form). Plain `args: ..Any` keeps the existing
`[]Any` slice path so stdlib's `format`/`print` continue
unchanged. The map is saved/restored across nested calls
mirroring `comptime_param_nodes`.
- `packArgNodeAt(ie)` returns the call-arg node when an
index_expr matches `<pack_name>[<comptime_int_literal>]`
with the index in range; null otherwise (fall through to
standard slice indexing for runtime indices or non-pack
bases).
- `lowerIndexExpr` checks `packArgNodeAt` first; on a hit it
lowers the call arg node directly. `inferExprType`'s
`index_expr` arm does the parallel check so AST-level type
inference (e.g., for field-access type checking) sees the
concrete call-arg type.
`examples/156-pack-typed-index.sx` flips from
"field 'x' not found on type 'Any'" to `7` — `args[0].x` now
resolves through the concrete `Point` type instead of Any.
Out of scope (deferred): non-literal comptime indices
(`args[$i]` where `$i` is an arbitrary comptime expression);
`$args[$i]` in type positions (step 3); per-mono mangling
(monomorphisation stays inline-only).
195/195 example tests + `zig build test` green.
cd367847a9