Surface rename of the signed integer family: s1..s64 become i1..i64
(u1..u64, usize, isize unchanged). 'string' keeps the s-prefix arm in
name classification; width parsing moves to the i-prefix arm next to
isize.
Internal TypeId tags follow the surface (.s8/.s16/.s32/.s64 ->
.i8/.i16/.i32/.i64), as do mono-key mangle fragments (ptr_i64,
tu_i64_bool) and all display/diagnostic formatting (i{d}).
Migrated in the same sweep: stdlib + examples + issue repros + FFI C
companions (shared symbol names like ffi_id_i64), expected
stdout/stderr/ir snapshots, specs.md, readme.md, CLAUDE.md/AGENTS.md,
implementation_plan.md, docs/, issue writeups. Vendored stb_image and
historical flow state left untouched.
zig build test: 426/426; examples suite: 595/595.
Assigning to a nonexistent struct field (`p.q = 2` where Point has no `q`)
aborted the compiler with the `.unresolved` LLVM tripwire instead of a source
diagnostic (issue 0094). The lvalue field lookup never diagnosed a miss:
- `lowerAssignment`'s `.field_access` target left `field_ty = .unresolved` when
no struct field matched, then built `ptrTo(field_ty)` and stored — so a
pointer-to-`.unresolved` reached LLVM emission and tripped the panic.
- `lowerExprAsPtr`'s `.field_access` fallback returned
`structGepTyped(obj_ptr, 0, .s64, obj_ty)` on a miss — a silent field-0/`.s64`
default that mislowered the lvalue.
Both sites now reuse the read path's `emitFieldError` (the exact facility
`lowerFieldAccessOnType` uses), so read and write reject identically with
`field 'q' not found on type 'Point'`. `lowerExprAsPtr` also resolves
union/tagged-union fields via `union_gep` (the old `.s64` fallback was silently
standing in for union field access — e.g. `u.a[0] = v`), so that path is fixed,
not just made loud. The `types.zig` tripwire is untouched: the fix is to never
produce `.unresolved` for a missing-field store.
Regression tests:
- examples/1145-diagnostics-missing-struct-field-assign.sx — negative, both
sites error, exit 1.
- examples/0165-types-nested-struct-field-assign.sx — positive, nested struct
field write + address-of a matched field still work.
- src/ir/lower.test.zig — lowering unit test asserting the field-not-found
diagnostic for a missing-field assignment.
