lang: rename signed integer types sN -> iN

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.

library/modules/std/fs.sx

@@ -24,36 +24,36 @@ libc :: #library "c";
 // API below wraps them. Users should not call these directly.
 //
 // macOS `open` is variadic in C (`int open(const char*, int, ...)`);
-// declared with `..args: []s32` so the mode is passed via the C
+// declared with `..args: []i32` so the mode is passed via the C
 // variadic tail. Without that, the mode arg goes to the wrong
 // register on arm64 and the file ends up with mode 0.
 
-open   :: (path: [:0]u8, flags: s32, ..args: []s32) -> s32 #foreign libc;
-close  :: (fd: s32) -> s32 #foreign libc;
-read   :: (fd: s32, buf: [*]u8, count: usize) -> isize #foreign libc;
-write  :: (fd: s32, buf: [*]u8, count: usize) -> isize #foreign libc;
-lseek  :: (fd: s32, offset: s64, whence: s32) -> s64 #foreign libc;
-unlink :: (path: [:0]u8) -> s32 #foreign libc;
-rmdir  :: (path: [:0]u8) -> s32 #foreign libc;
-mkdir  :: (path: [:0]u8, mode: u32) -> s32 #foreign libc;
-access :: (path: [:0]u8, mode: s32) -> s32 #foreign libc;
-chmod  :: (path: [:0]u8, mode: u32) -> s32 #foreign libc;
-rename :: (oldp: [:0]u8, newp: [:0]u8) -> s32 #foreign libc;
+open   :: (path: [:0]u8, flags: i32, ..args: []i32) -> i32 #foreign libc;
+close  :: (fd: i32) -> i32 #foreign libc;
+read   :: (fd: i32, buf: [*]u8, count: usize) -> isize #foreign libc;
+write  :: (fd: i32, buf: [*]u8, count: usize) -> isize #foreign libc;
+lseek  :: (fd: i32, offset: i64, whence: i32) -> i64 #foreign libc;
+unlink :: (path: [:0]u8) -> i32 #foreign libc;
+rmdir  :: (path: [:0]u8) -> i32 #foreign libc;
+mkdir  :: (path: [:0]u8, mode: u32) -> i32 #foreign libc;
+access :: (path: [:0]u8, mode: i32) -> i32 #foreign libc;
+chmod  :: (path: [:0]u8, mode: u32) -> i32 #foreign libc;
+rename :: (oldp: [:0]u8, newp: [:0]u8) -> i32 #foreign libc;
 
 // macOS POSIX constants. Linux values differ; split into platform-
 // conditional includes when we gain a Linux host.
-O_RDONLY :s32: 0x0000;
-O_WRONLY :s32: 0x0001;
-O_RDWR   :s32: 0x0002;
-O_APPEND :s32: 0x0008;
-O_CREAT  :s32: 0x0200;
-O_TRUNC  :s32: 0x0400;
+O_RDONLY :i32: 0x0000;
+O_WRONLY :i32: 0x0001;
+O_RDWR   :i32: 0x0002;
+O_APPEND :i32: 0x0008;
+O_CREAT  :i32: 0x0200;
+O_TRUNC  :i32: 0x0400;
 
-SEEK_SET :s32: 0;
-SEEK_CUR :s32: 1;
-SEEK_END :s32: 2;
+SEEK_SET :i32: 0;
+SEEK_CUR :i32: 1;
+SEEK_END :i32: 2;
 
-F_OK :s32: 0;
+F_OK :i32: 0;
 
 // ── Public types ─────────────────────────────────────────────────────
 
@@ -67,7 +67,7 @@ OpenMode :: enum {
 SeekFrom :: enum { set; current; end; }
 
 File :: struct {
-    fd: s32 = -1;
+    fd: i32 = -1;
 
     is_valid :: (self: *File) -> bool { self.fd >= 0 }
 
@@ -78,19 +78,19 @@ File :: struct {
         rc == 0
     }
 
-    read :: (self: *File, buf: string) -> s64 {
+    read :: (self: *File, buf: string) -> i64 {
         if self.fd < 0 { return -1; }
         n := read(self.fd, buf.ptr, xx buf.len);
-        cast(s64) n
+        cast(i64) n
     }
 
-    write :: (self: *File, data: string) -> s64 {
+    write :: (self: *File, data: string) -> i64 {
         if self.fd < 0 { return -1; }
         n := write(self.fd, data.ptr, xx data.len);
-        cast(s64) n
+        cast(i64) n
     }
 
-    seek :: (self: *File, offset: s64, whence: SeekFrom) -> s64 {
+    seek :: (self: *File, offset: i64, whence: SeekFrom) -> i64 {
         if self.fd < 0 { return -1; }
         w := SEEK_SET;
         if whence == .current { w = SEEK_CUR; }
@@ -105,7 +105,7 @@ File :: struct {
 // idea for `delete_file`/`delete_dir` vs libc's `unlink`/`rmdir`,
 // `set_mode` vs libc's `chmod`, etc.
 
-mode_to_flags :: (m: OpenMode) -> s32 {
+mode_to_flags :: (m: OpenMode) -> i32 {
     if m == .read       { return O_RDONLY; }
     if m == .write      { return O_WRONLY | O_CREAT | O_TRUNC; }
     if m == .append     { return O_WRONLY | O_CREAT | O_APPEND; }
@@ -133,7 +133,7 @@ read_file :: (path: [:0]u8) -> ?string {
     buf := cstring(size);
     n := read(fd, buf.ptr, xx size);
     close(fd);
-    if cast(s64) n != size { return null; }
+    if cast(i64) n != size { return null; }
     buf
 }
 
@@ -143,7 +143,7 @@ write_file :: (path: [:0]u8, data: string) -> bool {
     if fd < 0 { return false; }
     n := write(fd, data.ptr, xx data.len);
     close(fd);
-    cast(s64) n == cast(s64) data.len
+    cast(i64) n == cast(i64) data.len
 }
 
 append_file :: (path: [:0]u8, data: string) -> bool {
@@ -151,7 +151,7 @@ append_file :: (path: [:0]u8, data: string) -> bool {
     if fd < 0 { return false; }
     n := write(fd, data.ptr, xx data.len);
     close(fd);
-    cast(s64) n == cast(s64) data.len
+    cast(i64) n == cast(i64) data.len
 }
 
 // ── Single-syscall ops ───────────────────────────────────────────────