diff --git a/crates/ghostty-apprt-gtk/src/class/application.rs b/crates/ghostty-apprt-gtk/src/class/application.rs
index 752a9b9..96c2cf7 100644
--- a/crates/ghostty-apprt-gtk/src/class/application.rs
+++ b/crates/ghostty-apprt-gtk/src/class/application.rs
@@ -1138,12 +1138,13 @@ impl Application {
                 }
                 if let Some(v) = s.strip_prefix("--working-directory=") {
                     // D-Bus strings are plain UTF-8, including literal U+FDD0.
-                    working_directory =
-                        Some(ghostty_os::osbytes::EncodedOs::from_plain_text(v.trim()));
+                    working_directory = Some(ghostty_os::osbytes::EncodedOs::from_plain_text(
+                        trim_ascii_whitespace(v),
+                    ));
                     continue;
                 }
                 if let Some(v) = s.strip_prefix("--title=") {
-                    title = Some(v.trim().to_owned());
+                    title = Some(trim_ascii_whitespace(v).to_owned());
                 }
             }
         }
@@ -1869,3 +1870,30 @@ impl Drop for ReadyGuard {
 fn scopeguard_ready() -> ReadyGuard {
     ReadyGuard
 }
+
+/// `std.mem.trim(u8, v, &std.ascii.whitespace)`: only ASCII whitespace
+/// (space, `\t`, `\n`, VT, FF, `\r`) is trimmed, never Unicode whitespace
+/// such as U+00A0.
+fn trim_ascii_whitespace(v: &str) -> &str {
+    v.trim_matches(|c: char| matches!(c, ' ' | '\t' | '\n' | '\r' | '\x0b' | '\x0c'))
+}
+
+#[cfg(test)]
+mod trim_tests {
+    use super::trim_ascii_whitespace;
+
+    #[test]
+    fn new_window_arguments_trim_only_ascii_whitespace() {
+        assert_eq!(
+            trim_ascii_whitespace(" \t\n\r\x0b\x0c/tmp/a b \n"),
+            "/tmp/a b"
+        );
+        assert_eq!(trim_ascii_whitespace("/tmp/name\u{a0}"), "/tmp/name\u{a0}");
+        assert_eq!(
+            trim_ascii_whitespace("\u{a0}title\u{2003} "),
+            "\u{a0}title\u{2003}"
+        );
+        assert_eq!(trim_ascii_whitespace("\x0btitle\x0b"), "title");
+        assert_eq!(trim_ascii_whitespace(" \t "), "");
+    }
+}
diff --git a/crates/ghostty-apprt-gtk/src/css.rs b/crates/ghostty-apprt-gtk/src/css.rs
index 0c2c21e..c692a68 100644
--- a/crates/ghostty-apprt-gtk/src/css.rs
+++ b/crates/ghostty-apprt-gtk/src/css.rs
@@ -110,8 +110,8 @@ impl CssProviders {
 
         for p in &config.gtk_custom_css.value {
             let (path, optional) = match p {
-                Path::Optional(path) => (path.to_path(), true),
-                Path::Required(path) => (path.to_path(), false),
+                Path::Optional(path) => (path.to_syscall_path(), true),
+                Path::Required(path) => (path.to_syscall_path(), false),
             };
             let path = match path {
                 Ok(path) => path,
diff --git a/crates/ghostty-cli/src/ssh_cache/entry.rs b/crates/ghostty-cli/src/ssh_cache/entry.rs
index b23c3e2..c566ac4 100644
--- a/crates/ghostty-cli/src/ssh_cache/entry.rs
+++ b/crates/ghostty-cli/src/ssh_cache/entry.rs
@@ -40,7 +40,7 @@ impl Entry {
         let hostname = iter.next()?;
         let timestamp_str = iter.next()?;
         let terminfo_version = iter.next().unwrap_or("xterm-ghostty");
-        let timestamp = match timestamp_str.parse::<i64>() {
+        let timestamp = match ghostty_os::zig_fmt::parse_int::<i64>(timestamp_str.as_bytes(), 10) {
             Ok(t) => t,
             Err(err) => {
                 log::warn!("Invalid timestamp in cache entry: {timestamp_str} err={err}");
diff --git a/crates/ghostty-config/src/cli_args.rs b/crates/ghostty-config/src/cli_args.rs
index b49c740..ecb4412 100644
--- a/crates/ghostty-config/src/cli_args.rs
+++ b/crates/ghostty-config/src/cli_args.rs
@@ -506,6 +506,42 @@ pub fn parse_packed_struct_with(
     Ok(())
 }
 
+/// Zig's `@max` on floats: a NaN operand yields the other operand and
+/// `max(+0, -0)` is `+0`.
+#[must_use]
+pub fn zig_max(a: f64, b: f64) -> f64 {
+    if a.is_nan() {
+        b
+    } else if b.is_nan() {
+        a
+    } else if a == b {
+        if a.is_sign_negative() { b } else { a }
+    } else {
+        a.max(b)
+    }
+}
+
+/// Zig's `@min` on floats: a NaN operand yields the other operand and
+/// `min(+0, -0)` is `-0`.
+#[must_use]
+pub fn zig_min(a: f64, b: f64) -> f64 {
+    if a.is_nan() {
+        b
+    } else if b.is_nan() {
+        a
+    } else if a == b {
+        if a.is_sign_negative() { a } else { b }
+    } else {
+        a.min(b)
+    }
+}
+
+/// `std.math.clamp` on floats (`@max(lower, @min(val, upper))`).
+#[must_use]
+pub fn zig_clamp(val: f64, lower: f64, upper: f64) -> f64 {
+    zig_max(lower, zig_min(val, upper))
+}
+
 pub fn parse_bool(v: &str) -> Result<bool, ArgError> {
     match v {
         "1" | "t" | "T" | "true" => Ok(true),
@@ -514,42 +550,6 @@ pub fn parse_bool(v: &str) -> Result<bool, ArgError> {
     }
 }
 
-/// Parse an integer like Zig's `std.fmt.parseInt(T, s, 0)`: optional sign,
-/// optional `0x`/`0o`/`0b` prefix, underscores between digits allowed.
-pub fn parse_int_base0(s: &str) -> Option<i128> {
-    let (neg, rest) = match s.as_bytes().first()? {
-        b'-' => (true, &s[1..]),
-        b'+' => (false, &s[1..]),
-        _ => (false, s),
-    };
-    let (base, digits) = if rest.len() >= 2 && rest.as_bytes()[0] == b'0' {
-        match rest.as_bytes()[1] {
-            b'x' => (16, &rest[2..]),
-            b'o' => (8, &rest[2..]),
-            b'b' => (2, &rest[2..]),
-            _ => (10, rest),
-        }
-    } else {
-        (10, rest)
-    };
-    if digits.is_empty() {
-        return None;
-    }
-    let db = digits.as_bytes();
-    if db[0] == b'_' || db[db.len() - 1] == b'_' || digits.contains("__") {
-        return None;
-    }
-    let mut acc: i128 = 0;
-    for &c in db {
-        if c == b'_' {
-            continue;
-        }
-        let d = i128::from((c as char).to_digit(base)?);
-        acc = acc.checked_mul(i128::from(base))?.checked_add(d)?;
-    }
-    Some(if neg { -acc } else { acc })
-}
-
 // ---------------------------------------------------------------------
 // ConfigField impls for primitives
 
@@ -580,10 +580,9 @@ macro_rules! impl_int_field {
             }
 
             fn parse_bytes(&mut self, value: Option<&[u8]>) -> Result<(), ArgError> {
-        let value = crate::cli_args::text_value(value)?;
                 let v = value.ok_or(ArgError::ValueRequired)?;
-                let n = parse_int_base0(v).ok_or(ArgError::InvalidValue)?;
-                *self = <$t>::try_from(n).map_err(|_| ArgError::InvalidValue)?;
+                *self = ghostty_os::zig_fmt::parse_int::<$t>(v, 0)
+                    .map_err(|_| ArgError::InvalidValue)?;
                 Ok(())
             }
 
@@ -615,14 +614,14 @@ macro_rules! impl_float_field {
             }
 
             fn parse_bytes(&mut self, value: Option<&[u8]>) -> Result<(), ArgError> {
-        let value = crate::cli_args::text_value(value)?;
                 let v = value.ok_or(ArgError::ValueRequired)?;
-                *self = v.parse::<$t>().map_err(|_| ArgError::InvalidValue)?;
+                *self = ghostty_os::zig_fmt::parse_float::<$t>(v)
+                    .map_err(|_| ArgError::InvalidValue)?;
                 Ok(())
             }
 
             fn format_entry(&self, f: &mut EntryFormatter<'_>) -> fmt::Result {
-                writeln!(f.writer, "{} = {}", f.name, self)
+                writeln!(f.writer, "{} = {}", f.name, ghostty_os::zig_fmt::format_float_d(*self))
             }
         }
     )*};
@@ -1642,12 +1641,45 @@ mod tests {
     }
 
     #[test]
-    fn parse_int_base0_forms() {
-        assert_eq!(parse_int_base0("0x_1"), None);
-        assert_eq!(parse_int_base0("1_000"), Some(1000));
-        assert_eq!(parse_int_base0("-0b11"), Some(-3));
-        assert_eq!(parse_int_base0("0o17"), Some(15));
-        assert_eq!(parse_int_base0(""), None);
+    fn numeric_fields_use_zig_parse_int_and_parse_float_grammars() {
+        let mut n = 0u32;
+        n.parse_bytes(Some(b"0X10")).unwrap();
+        assert_eq!(n, 16);
+        n.parse_bytes(Some(b"1__0")).unwrap();
+        assert_eq!(n, 10);
+        n.parse_bytes(Some(b"+0b1_1")).unwrap();
+        assert_eq!(n, 3);
+        for bad in ["0x_1", "_1", "1_", "-1", "0x", "", " 1", "1 ", "\u{e9}"] {
+            assert_eq!(
+                n.parse_bytes(Some(bad.as_bytes())),
+                Err(ArgError::InvalidValue),
+                "{bad:?}"
+            );
+        }
+        assert_eq!(n.parse_bytes(None), Err(ArgError::ValueRequired));
+        let mut i = 0i16;
+        i.parse_bytes(Some(b"-0O17")).unwrap();
+        assert_eq!(i, -15);
+        assert_eq!(i.parse_bytes(Some(b"40000")), Err(ArgError::InvalidValue));
+        // Invalid UTF-8 is just an invalid character for numbers.
+        assert_eq!(n.parse_bytes(Some(b"\xff")), Err(ArgError::InvalidValue));
+
+        let mut f = 0f32;
+        f.parse_bytes(Some(b"1_4")).unwrap();
+        assert_eq!(f, 14.0);
+        f.parse_bytes(Some(b"0x1.cp+3")).unwrap();
+        assert_eq!(f, 14.0);
+        f.parse_bytes(Some(b"-INF")).unwrap();
+        assert_eq!(f, f32::NEG_INFINITY);
+        f.parse_bytes(Some(b"nan")).unwrap();
+        assert!(f.is_nan());
+        for bad in ["1__4", "infx", ".", "1e", " 1", "0x"] {
+            assert_eq!(
+                f.parse_bytes(Some(bad.as_bytes())),
+                Err(ArgError::InvalidValue),
+                "{bad:?}"
+            );
+        }
     }
 
     #[test]
diff --git a/crates/ghostty-config/src/command.rs b/crates/ghostty-config/src/command.rs
index ba4b522..b736386 100644
--- a/crates/ghostty-config/src/command.rs
+++ b/crates/ghostty-config/src/command.rs
@@ -63,55 +63,14 @@ impl Iterator for ArgIterator {
     }
 }
 
-/// Best-effort shell string splitter matching Zig's
-/// `std.process.ArgIteratorGeneral(.{})` (whitespace separated, double
-/// quotes group, backslashes only special before a double quote).
+/// Zig's `std.process.ArgIteratorGeneral(.{})`.
 fn split_general(b: &[u8]) -> Vec<EncodedOs> {
-    let mut out = vec![];
-    let mut i = 0;
-    loop {
-        // skip whitespace
-        while i < b.len() && (b[i] == b' ' || b[i] == b'\t') {
-            i += 1;
-        }
-        if i >= b.len() {
-            break;
-        }
-
-        let mut cur: Vec<u8> = vec![];
-        let mut quoted = false;
-        while i < b.len() {
-            match b[i] {
-                b' ' | b'\t' if !quoted => break,
-                b'\\' => {
-                    let mut n = 0;
-                    while i < b.len() && b[i] == b'\\' {
-                        n += 1;
-                        i += 1;
-                    }
-                    if i < b.len() && b[i] == b'"' {
-                        cur.extend(std::iter::repeat_n(b'\\', n / 2));
-                        if n % 2 == 1 {
-                            cur.push(b'"');
-                            i += 1;
-                        }
-                    } else {
-                        cur.extend(std::iter::repeat_n(b'\\', n));
-                    }
-                }
-                b'"' => {
-                    quoted = !quoted;
-                    i += 1;
-                }
-                c => {
-                    cur.push(c);
-                    i += 1;
-                }
-            }
-        }
-        out.push(EncodedOs::from_bytes(&cur));
-    }
-    out
+    ghostty_os::arg_iterator::ArgIteratorGeneral::new(
+        ghostty_os::arg_iterator::Options::default(),
+        b,
+    )
+    .map(|arg| EncodedOs::from_bytes(&arg))
+    .collect()
 }
 
 impl Command {
@@ -259,6 +218,13 @@ mod tests {
         assert_eq!(args, ["echo", "hello world", "a\"b"]);
     }
 
+    #[test]
+    fn command_arg_iterator_shell_splits_cr_lf_tab_like_zig() {
+        let v = Command::Shell(EncodedOs::from_bytes(b"bash\n-i\r\tx \"a\nb\"\0ignored"));
+        let args: Vec<EncodedOs> = v.arg_iterator().collect();
+        assert_eq!(args, ["bash", "-i", "x", "a\nb"]);
+    }
+
     #[test]
     fn command_arg_iterator_direct() {
         let v = Command::Direct(vec!["echo".into(), "hello world".into()]);
diff --git a/crates/ghostty-config/src/config.rs b/crates/ghostty-config/src/config.rs
index 426e381..01a52c3 100644
--- a/crates/ghostty-config/src/config.rs
+++ b/crates/ghostty-config/src/config.rs
@@ -4224,7 +4224,7 @@ impl Config {
                 continue;
             }
 
-            let file = match path.to_path().and_then(std::fs::File::open) {
+            let file = match path.to_syscall_path().and_then(std::fs::File::open) {
                 Ok(f) => f,
                 Err(err) => {
                     if err.kind() != std::io::ErrorKind::NotFound || !optional {
@@ -4564,16 +4564,19 @@ impl Config {
         }
 
         // Clamp our mouse scroll multiplier
+        // (`@min(10_000, @max(0.01, v))`: NaN becomes the minimum.)
+        let zmin = cli_args::zig_min;
+        let zmax = cli_args::zig_max;
         self.mouse_scroll_multiplier.precision =
-            self.mouse_scroll_multiplier.precision.clamp(0.01, 10_000.0);
+            zmin(10_000.0, zmax(0.01, self.mouse_scroll_multiplier.precision));
         self.mouse_scroll_multiplier.discrete =
-            self.mouse_scroll_multiplier.discrete.clamp(0.01, 10_000.0);
+            zmin(10_000.0, zmax(0.01, self.mouse_scroll_multiplier.discrete));
 
         // Clamp our split opacity
-        self.unfocused_split_opacity = self.unfocused_split_opacity.clamp(0.15, 1.0);
+        self.unfocused_split_opacity = zmin(1.0, zmax(0.15, self.unfocused_split_opacity));
 
         // Clamp our contrast
-        self.minimum_contrast = self.minimum_contrast.clamp(1.0, 21.0);
+        self.minimum_contrast = zmin(21.0, zmax(1.0, self.minimum_contrast));
 
         // Minimum window size
         if self.window_width > 0 {
@@ -4606,7 +4609,7 @@ impl Config {
             self.auto_update_channel = Some(ReleaseChannel::Stable);
         }
 
-        self.faint_opacity = self.faint_opacity.clamp(0.0, 1.0);
+        self.faint_opacity = cli_args::zig_clamp(self.faint_opacity, 0.0, 1.0);
 
         // Finalize key remapping set for efficient lookups
         self.key_remap.finalize();
@@ -4753,14 +4756,37 @@ impl Iterator for ChangeIterator<'_> {
     }
 }
 
-/// Name of an IO error like Zig's error names (best effort), used in
-/// user-visible diagnostics.
+/// Name of an IO error like Zig's `{}` formatting of an error value
+/// (`error.FileNotFound`), used in user-visible diagnostics.
 fn zig_io_error_name(err: &std::io::Error) -> String {
     use std::io::ErrorKind;
+    #[cfg(unix)]
+    if let Some(errno) = err.raw_os_error() {
+        let name = match errno {
+            2 => Some("FileNotFound"),
+            13 => Some("AccessDenied"),
+            1 => Some("PermissionDenied"),
+            21 => Some("IsDir"),
+            20 => Some("NotDir"),
+            40 => Some("SymLinkLoop"),
+            36 => Some("NameTooLong"),
+            24 => Some("ProcessFdQuotaExceeded"),
+            23 => Some("SystemFdQuotaExceeded"),
+            12 => Some("SystemResources"),
+            19 => Some("NoDevice"),
+            16 => Some("DeviceBusy"),
+            26 => Some("FileBusy"),
+            30 => Some("ReadOnlyFileSystem"),
+            _ => None,
+        };
+        if let Some(name) = name {
+            return format!("error.{name}");
+        }
+    }
     match err.kind() {
-        ErrorKind::NotFound => "FileNotFound".to_string(),
-        ErrorKind::PermissionDenied => "AccessDenied".to_string(),
-        _ => err.to_string(),
+        ErrorKind::NotFound => "error.FileNotFound".to_string(),
+        ErrorKind::PermissionDenied => "error.AccessDenied".to_string(),
+        _ => "error.Unexpected".to_string(),
     }
 }
 
diff --git a/crates/ghostty-config/src/metric_modifier.rs b/crates/ghostty-config/src/metric_modifier.rs
index 29d3f04..a6e7b7c 100644
--- a/crates/ghostty-config/src/metric_modifier.rs
+++ b/crates/ghostty-config/src/metric_modifier.rs
@@ -30,13 +30,18 @@ impl MetricModifier {
     /// Parses the modifier value. If the value ends in "%" it is assumed
     /// to be a percent, otherwise the value is parsed as an integer.
     pub fn parse(input: &str) -> Result<MetricModifier, ArgError> {
+        Self::parse_bytes(input.as_bytes())
+    }
+
+    /// [`MetricModifier::parse`] over the original bytes (Zig never
+    /// validates UTF-8; every failure is `InvalidFormat`).
+    pub fn parse_bytes(input: &[u8]) -> Result<MetricModifier, ArgError> {
         if input.is_empty() {
             return Err(ArgError::other("InvalidFormat"));
         }
 
-        if let Some(num) = input.strip_suffix('%') {
-            let mut percent = num
-                .parse::<f64>()
+        if let Some(num) = input.strip_suffix(b"%") {
+            let mut percent = ghostty_os::zig_fmt::parse_float::<f64>(num)
                 .map_err(|_| ArgError::other("InvalidFormat"))?;
             percent /= 100.0;
 
@@ -46,15 +51,14 @@ impl MetricModifier {
             return Ok(MetricModifier::Percent(1.0 + percent));
         }
 
-        input
-            .parse::<i32>()
+        ghostty_os::zig_fmt::parse_int::<i32>(input, 10)
             .map(MetricModifier::Absolute)
             .map_err(|_| ArgError::other("InvalidFormat"))
     }
 
     /// So it works with the config framework.
-    pub fn parse_cli_value(input: Option<&str>) -> Result<MetricModifier, ArgError> {
-        Self::parse(input.ok_or(ArgError::ValueRequired)?)
+    pub fn parse_cli_value(input: Option<&[u8]>) -> Result<MetricModifier, ArgError> {
+        Self::parse_bytes(input.ok_or(ArgError::ValueRequired)?)
     }
 
     /// Apply a modifier to an integer value (saturating, clamped at zero for
@@ -100,14 +104,16 @@ impl MetricModifier {
 
 impl ConfigField for MetricModifier {
     fn parse_bytes(&mut self, value: Option<&[u8]>) -> Result<(), ArgError> {
-        let value = crate::cli_args::text_value(value)?;
         *self = Self::parse_cli_value(value)?;
         Ok(())
     }
 
     fn format_entry(&self, f: &mut EntryFormatter<'_>) -> fmt::Result {
         let s = match self {
-            MetricModifier::Percent(v) => format!("{}%", (v - 1.0) * 100.0),
+            MetricModifier::Percent(v) => format!(
+                "{}%",
+                ghostty_os::zig_fmt::format_float_d((v - 1.0) * 100.0)
+            ),
             MetricModifier::Absolute(v) => format!("{v}"),
         };
         f.format_entry(&s)
diff --git a/crates/ghostty-config/src/path.rs b/crates/ghostty-config/src/path.rs
index 94c058d..5414db7 100644
--- a/crates/ghostty-config/src/path.rs
+++ b/crates/ghostty-config/src/path.rs
@@ -154,7 +154,7 @@ impl Path {
         // Make sure the base directory can be opened.
         std::fs::read_dir(&base_path)?;
 
-        let full = base_path.join(path.to_path()?);
+        let full = base_path.join(path.to_syscall_path()?);
         let abs = match std::fs::canonicalize(&full) {
             Ok(p) => EncodedOs::from_path(&p),
             Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
@@ -392,6 +392,31 @@ mod tests {
         assert!(diags.is_empty());
     }
 
+    #[cfg(unix)]
+    #[test]
+    fn expand_interior_nul_resolves_the_c_string_prefix_like_zig() {
+        let tmp = ghostty_os::TempDir::init().unwrap();
+        let base = std::fs::canonicalize(tmp.path()).unwrap();
+        std::fs::write(base.join("exists"), b"x").unwrap();
+
+        // The syscall sees only the prefix, which exists: the real path of
+        // the prefix replaces the value.
+        let mut p = Path::Required(EncodedOs::from_bytes(b"exists\0tail"));
+        let mut diags = DiagnosticList::default();
+        p.expand(&EncodedOs::from_path(&base), &mut diags).unwrap();
+        assert_eq!(diags.items().len(), 0);
+        assert_eq!(p.path().to_path().unwrap(), base.join("exists"));
+
+        // The prefix is missing: the whole value is resolved lexically.
+        let mut p = Path::Required(EncodedOs::from_bytes(b"missing\0tail"));
+        p.expand(&EncodedOs::from_path(&base), &mut diags).unwrap();
+        assert_eq!(diags.items().len(), 0);
+        assert_eq!(
+            p.path().to_bytes(),
+            [base.as_os_str().as_encoded_bytes(), b"/missing\0tail"].concat()
+        );
+    }
+
     #[cfg(unix)]
     #[test]
     fn expand_symlink_to_non_utf8_target_round_trips() {
diff --git a/crates/ghostty-config/src/types_a.rs b/crates/ghostty-config/src/types_a.rs
index 1555021..db28bcd 100644
--- a/crates/ghostty-config/src/types_a.rs
+++ b/crates/ghostty-config/src/types_a.rs
@@ -8,7 +8,7 @@ use ghostty_vt::color::{DEFAULT as DEFAULT_PALETTE, Palette as TermPalette, Pale
 
 use crate::{
     c_value::CValue,
-    cli_args::{ArgError, ConfigField, parse_int_base0, trim_ws},
+    cli_args::{ArgError, ConfigField, trim_ws},
     clipboard_codepoint_map::{ClipboardCodepointMap, Entry as ClipboardEntry, Replacement},
     config_enum,
     config_packed,
@@ -242,11 +242,18 @@ impl Color {
 
     /// Zig: `Color.parseCLI(input)` (static form returning a new value).
     pub fn from_cli(input: Option<&str>) -> Result<Color, ArgError> {
+        Color::from_cli_bytes(input.map(str::as_bytes))
+    }
+
+    /// [`Color::from_cli`] over the original bytes: Zig never validates
+    /// UTF-8 here, so a stray byte is an `InvalidCharacter` (or
+    /// `InvalidValue` for a wrong length), not a generic invalid value.
+    pub fn from_cli_bytes(input: Option<&[u8]>) -> Result<Color, ArgError> {
         let input = input.ok_or(ArgError::ValueRequired)?;
         // Trim any whitespace before processing
-        let trimmed = trim_ws(input);
+        let trimmed = crate::cli_args::trim_bytes(input);
 
-        if let Some(rgb) = ghostty_vt::x11_color::get(trimmed) {
+        if let Some(rgb) = ghostty_vt::x11_color::get_bytes(trimmed) {
             return Ok(Color {
                 r: rgb.r,
                 g: rgb.g,
@@ -254,7 +261,7 @@ impl Color {
             });
         }
 
-        Color::from_hex(trimmed)
+        Color::from_hex_bytes(trimmed)
     }
 
     /// Format the color as a string.
@@ -266,8 +273,13 @@ impl Color {
     /// fromHex parses a color from a hex value such as #RRGGBB. The "#"
     /// is optional.
     pub fn from_hex(input: &str) -> Result<Color, ArgError> {
+        Color::from_hex_bytes(input.as_bytes())
+    }
+
+    /// [`Color::from_hex`] over bytes.
+    pub fn from_hex_bytes(input: &[u8]) -> Result<Color, ArgError> {
         // Trim the beginning '#' if it exists
-        let trimmed = input.strip_prefix('#').unwrap_or(input).as_bytes();
+        let trimmed = input.strip_prefix(b"#").unwrap_or(input);
         if trimmed.len() != 6 && trimmed.len() != 3 {
             return Err(ArgError::InvalidValue);
         }
@@ -282,7 +294,7 @@ impl Color {
         };
 
         let digit = |c: u8| -> Result<u8, ArgError> {
-            (c as char)
+            char::from(c)
                 .to_digit(16)
                 .map(|d| d as u8)
                 .ok_or_else(|| ArgError::other("InvalidCharacter"))
@@ -308,8 +320,7 @@ impl ConfigField for Color {
     }
 
     fn parse_bytes(&mut self, input: Option<&[u8]>) -> Result<(), ArgError> {
-        let input = crate::cli_args::text_value(input)?;
-        *self = Color::from_cli(input)?;
+        *self = Color::from_cli_bytes(input)?;
         Ok(())
     }
 
@@ -336,11 +347,16 @@ impl Default for TerminalColor {
 impl TerminalColor {
     /// Zig: `TerminalColor.parseCLI(input)`.
     pub fn from_cli(input: Option<&str>) -> Result<TerminalColor, ArgError> {
+        TerminalColor::from_cli_bytes(input.map(str::as_bytes))
+    }
+
+    /// [`TerminalColor::from_cli`] over bytes.
+    pub fn from_cli_bytes(input: Option<&[u8]>) -> Result<TerminalColor, ArgError> {
         let input = input.ok_or(ArgError::ValueRequired)?;
         match input {
-            "cell-foreground" => Ok(TerminalColor::CellForeground),
-            "cell-background" => Ok(TerminalColor::CellBackground),
-            _ => Ok(TerminalColor::Color(Color::from_cli(Some(input))?)),
+            b"cell-foreground" => Ok(TerminalColor::CellForeground),
+            b"cell-background" => Ok(TerminalColor::CellBackground),
+            _ => Ok(TerminalColor::Color(Color::from_cli_bytes(Some(input))?)),
         }
     }
 
@@ -355,8 +371,7 @@ impl TerminalColor {
 
 impl ConfigField for TerminalColor {
     fn parse_bytes(&mut self, input: Option<&[u8]>) -> Result<(), ArgError> {
-        let input = crate::cli_args::text_value(input)?;
-        *self = TerminalColor::from_cli(input)?;
+        *self = TerminalColor::from_cli_bytes(input)?;
         Ok(())
     }
 
@@ -385,18 +400,22 @@ impl Default for BoldColor {
 impl BoldColor {
     /// Zig: `BoldColor.parseCLI(input)`.
     pub fn from_cli(input: Option<&str>) -> Result<BoldColor, ArgError> {
+        BoldColor::from_cli_bytes(input.map(str::as_bytes))
+    }
+
+    /// [`BoldColor::from_cli`] over bytes.
+    pub fn from_cli_bytes(input: Option<&[u8]>) -> Result<BoldColor, ArgError> {
         let input = input.ok_or(ArgError::ValueRequired)?;
-        if input == "bright" {
+        if input == b"bright" {
             return Ok(BoldColor::Bright);
         }
-        Ok(BoldColor::Color(Color::from_cli(Some(input))?))
+        Ok(BoldColor::Color(Color::from_cli_bytes(Some(input))?))
     }
 }
 
 impl ConfigField for BoldColor {
     fn parse_bytes(&mut self, input: Option<&[u8]>) -> Result<(), ArgError> {
-        let input = crate::cli_args::text_value(input)?;
-        *self = BoldColor::from_cli(input)?;
+        *self = BoldColor::from_cli_bytes(input)?;
         Ok(())
     }
 
@@ -419,7 +438,6 @@ impl ConfigField for ColorList {
     }
 
     fn parse_bytes(&mut self, input: Option<&[u8]>) -> Result<(), ArgError> {
-        let input = crate::cli_args::text_value(input)?;
         let input = input.ok_or(ArgError::ValueRequired)?;
         if input.is_empty() {
             return Err(ArgError::ValueRequired);
@@ -430,15 +448,15 @@ impl ConfigField for ColorList {
 
         // Split the input by commas and parse each color
         let mut count = 0usize;
-        for raw in input.split(',').filter(|s| !s.is_empty()) {
+        for raw in input.split(|b| *b == b',').filter(|s| !s.is_empty()) {
             count += 1;
             if count > 64 {
                 return Err(ArgError::InvalidValue);
             }
 
             // Trim whitespace from each color value
-            let trimmed = trim_ws(raw);
-            let color = Color::from_cli(Some(trimmed))?;
+            let trimmed = crate::cli_args::trim_bytes(raw);
+            let color = Color::from_cli_bytes(Some(trimmed))?;
             self.colors.push(color);
         }
 
@@ -488,21 +506,26 @@ impl ConfigField for Palette {
     }
 
     fn parse_bytes(&mut self, input: Option<&[u8]>) -> Result<(), ArgError> {
-        let input = crate::cli_args::text_value(input)?;
         let value = input.ok_or(ArgError::ValueRequired)?;
-        let eql_idx = value.find('=').ok_or(ArgError::InvalidValue)?;
+        let eql_idx = value
+            .iter()
+            .position(|b| *b == b'=')
+            .ok_or(ArgError::InvalidValue)?;
 
         // Parse the key part (trim whitespace)
-        let key_str = trim_ws(&value[..eql_idx]);
-        let key = match parse_int_base0(key_str) {
-            None => return Err(ArgError::other("InvalidCharacter")),
-            Some(n) if n < 0 => return Err(ArgError::other("InvalidCharacter")),
-            Some(n) if n > 255 => return Err(ArgError::other("Overflow")),
-            Some(n) => n as usize,
+        let key_str = crate::cli_args::trim_bytes(&value[..eql_idx]);
+        let key = match ghostty_os::zig_fmt::parse_int::<u8>(key_str, 0) {
+            Ok(n) => usize::from(n),
+            Err(ghostty_os::zig_fmt::ParseIntError::InvalidCharacter) => {
+                return Err(ArgError::other("InvalidCharacter"));
+            }
+            Err(ghostty_os::zig_fmt::ParseIntError::Overflow) => {
+                return Err(ArgError::other("Overflow"));
+            }
         };
 
         // Parse the color part (Color parsing will handle whitespace)
-        let rgb = Color::from_cli(Some(&value[eql_idx + 1..]))?;
+        let rgb = Color::from_cli_bytes(Some(&value[eql_idx + 1..]))?;
         self.value[key] = rgb.to_terminal_rgb();
         self.mask.set(key);
         Ok(())
@@ -698,7 +721,8 @@ impl ConfigField for RepeatableFontVariation {
         let key: &[u8; 4] = key.try_into().map_err(|_| ArgError::InvalidValue)?;
         self.list.push(Variation {
             id: VariationId::init(key),
-            value: value.parse::<f64>().map_err(|_| ArgError::InvalidValue)?,
+            value: ghostty_os::zig_fmt::parse_float::<f64>(value.as_bytes())
+                .map_err(|_| ArgError::InvalidValue)?,
         });
         Ok(())
     }
@@ -861,8 +885,7 @@ impl<'a> UnicodeRangeParser<'a> {
 
 /// `std.fmt.parseInt(u21, s, 16)` for plain hex digit strings.
 fn parse_u21_hex(s: &[u8]) -> Option<u32> {
-    let s = std::str::from_utf8(s).ok()?;
-    let v = u32::from_str_radix(s, 16).ok()?;
+    let v = ghostty_os::zig_fmt::parse_int::<u32>(s, 16).ok()?;
     (v <= 0x1f_ffff).then_some(v)
 }
 
@@ -1054,7 +1077,6 @@ pub struct RepeatableLink {
 
 impl ConfigField for RepeatableLink {
     fn parse_bytes(&mut self, _input: Option<&[u8]>) -> Result<(), ArgError> {
-        let _input = crate::cli_args::text_value(_input)?;
         Err(ArgError::other("NotImplemented"))
     }
 
diff --git a/crates/ghostty-config/src/types_b.rs b/crates/ghostty-config/src/types_b.rs
index 2be64ce..70c0301 100644
--- a/crates/ghostty-config/src/types_b.rs
+++ b/crates/ghostty-config/src/types_b.rs
@@ -413,7 +413,8 @@ impl ConfigField for MouseScrollMultiplier {
         match r {
             Ok(()) => *self = result,
             Err(ArgError::InvalidValue) => {
-                let v: f64 = input.parse().map_err(|_| ArgError::InvalidValue)?;
+                let v = ghostty_os::zig_fmt::parse_float::<f64>(input.as_bytes())
+                    .map_err(|_| ArgError::InvalidValue)?;
                 *self = MouseScrollMultiplier {
                     precision: v,
                     discrete: v,
@@ -427,7 +428,11 @@ impl ConfigField for MouseScrollMultiplier {
     fn format_entry(&self, f: &mut EntryFormatter<'_>) -> fmt::Result {
         fmt_str(
             f,
-            &format!("precision:{},discrete:{}", self.precision, self.discrete),
+            &format!(
+                "precision:{},discrete:{}",
+                ghostty_os::zig_fmt::format_float_d(self.precision),
+                ghostty_os::zig_fmt::format_float_d(self.discrete)
+            ),
         )
     }
 }
@@ -537,19 +542,21 @@ impl QuickTerminalSizeValue {
         }
     }
 
-    pub fn parse(input: &str) -> Result<Self, ArgError> {
+    pub fn parse(input: &[u8]) -> Result<Self, ArgError> {
         if input.is_empty() {
             return Err(ArgError::ValueRequired);
         }
 
-        if let Some(num) = input.strip_suffix("px") {
+        if let Some(num) = input.strip_suffix(b"px") {
             return Ok(Self::Pixels(
-                num.parse::<u32>().map_err(|_| ArgError::InvalidValue)?,
+                ghostty_os::zig_fmt::parse_int::<u32>(num, 10)
+                    .map_err(|_| ArgError::InvalidValue)?,
             ));
         }
 
-        if let Some(num) = input.strip_suffix('%') {
-            let percentage = num.parse::<f32>().map_err(|_| ArgError::InvalidValue)?;
+        if let Some(num) = input.strip_suffix(b"%") {
+            let percentage =
+                ghostty_os::zig_fmt::parse_float::<f32>(num).map_err(|_| ArgError::InvalidValue)?;
             if percentage < 0.0 {
                 return Err(ArgError::InvalidValue);
             }
@@ -630,15 +637,16 @@ impl ConfigField for QuickTerminalSize {
     }
 
     fn parse_bytes(&mut self, input: Option<&[u8]>) -> Result<(), ArgError> {
-        let input = crate::cli_args::text_value(input)?;
         let input = input.ok_or(ArgError::ValueRequired)?;
-        let mut it = input.split(',');
+        let mut it = input.split(|b| *b == b',');
 
-        let primary = trim_ws(it.next().ok_or(ArgError::ValueRequired)?);
+        let primary = crate::cli_args::trim_bytes(it.next().ok_or(ArgError::ValueRequired)?);
         self.primary = Some(QuickTerminalSizeValue::parse(primary)?);
 
         self.secondary = match it.next() {
-            Some(s) => Some(QuickTerminalSizeValue::parse(trim_ws(s))?),
+            Some(s) => Some(QuickTerminalSizeValue::parse(crate::cli_args::trim_bytes(
+                s,
+            ))?),
             None => None,
         };
 
@@ -824,15 +832,17 @@ impl ConfigField for BackgroundBlur {
     }
 
     fn parse_bytes(&mut self, input: Option<&[u8]>) -> Result<(), ArgError> {
-        let input = crate::cli_args::text_value(input)?;
         let Some(input) = input else {
             // Emulate behavior for bools
             *self = BackgroundBlur::True;
             return Ok(());
         };
+        // Only the bool/enum spellings need text; everything else is a
+        // `parseInt` over the raw bytes.
+        let text = std::str::from_utf8(input).unwrap_or("\u{fffd}");
 
         // Try to parse normal bools
-        if let Ok(b) = parse_bool(input) {
+        if let Ok(b) = parse_bool(text) {
             *self = if b {
                 BackgroundBlur::True
             } else {
@@ -842,7 +852,7 @@ impl ConfigField for BackgroundBlur {
         }
 
         // Try to parse enums (only void variants can be parsed this way)
-        match input {
+        match text {
             "macos-glass-regular" => {
                 *self = BackgroundBlur::MacosGlassRegular;
                 return Ok(());
@@ -854,11 +864,20 @@ impl ConfigField for BackgroundBlur {
             _ => {}
         }
 
-        let mut r = 0u8;
-        r.parse_cli(Some(input))
-            .map_err(|_| ArgError::InvalidValue)?;
+        // Zig writes `self.* = .{ .radius = parseInt(...) catch return ... }`
+        // in place: the union tag is switched to `radius` before the payload
+        // is computed, so a failed parse leaves a `radius` variant behind
+        // (observable in the oracle: an invalid value formats as `0`).
+        let mut r = match *self {
+            BackgroundBlur::Radius(v) => v,
+            _ => 0,
+        };
+        let parsed = ghostty_os::zig_fmt::parse_int::<u8>(input, 0);
+        if let Ok(v) = parsed {
+            r = v;
+        }
         *self = BackgroundBlur::Radius(r);
-        Ok(())
+        parsed.map(|_| ()).map_err(|_| ArgError::InvalidValue)
     }
 
     fn format_entry(&self, f: &mut EntryFormatter<'_>) -> fmt::Result {
@@ -1028,14 +1047,7 @@ pub const DURATION_UNITS: &[(&str, u64)] = &[
 
 /// `std.fmt.parseUnsigned(u64, s, 10)`.
 fn parse_unsigned_u64(s: &[u8]) -> Option<u64> {
-    if s.is_empty() || !s.iter().all(u8::is_ascii_digit) {
-        return None;
-    }
-    let mut acc: u64 = 0;
-    for &c in s {
-        acc = acc.checked_mul(10)?.checked_add(u64::from(c - b'0'))?;
-    }
-    Some(acc)
+    ghostty_os::zig_fmt::parse_unsigned::<u64>(s, 10).ok()
 }
 
 impl Duration {
@@ -1201,7 +1213,10 @@ pub struct WindowPadding {
 impl WindowPadding {
     pub fn parse(input: Option<&str>) -> Result<WindowPadding, ArgError> {
         let input = input.ok_or(ArgError::ValueRequired)?;
-        let p = |s: &str| s.parse::<u32>().map_err(|_| ArgError::InvalidValue);
+        let p = |s: &str| {
+            ghostty_os::zig_fmt::parse_int::<u32>(s.as_bytes(), 10)
+                .map_err(|_| ArgError::InvalidValue)
+        };
 
         if let Some(idx) = input.find(',') {
             let left = p(trim_ws(&input[..idx]))?;
diff --git a/crates/ghostty-config/tests/zig_parity.rs b/crates/ghostty-config/tests/zig_parity.rs
new file mode 100644
index 0000000..815dc53
--- /dev/null
+++ b/crates/ghostty-config/tests/zig_parity.rs
@@ -0,0 +1,147 @@
+//! Parity regressions found by differential runs against Ghostty 1.3.1:
+//! numeric grammars, field-specific error kinds for non-UTF-8 input and
+//! float formatting.
+#![allow(clippy::unwrap_used)]
+use ghostty_config::{cli_args::ArgError, config::Config};
+
+fn parse(key: &str, value: &[u8]) -> Result<Config, ArgError> {
+    let mut config = Config::default();
+    config.parse_field_bytes(key, Some(value))?;
+    Ok(config)
+}
+
+fn kind(key: &str, value: &[u8]) -> String {
+    parse(key, value).map_or_else(|e| e.to_string(), |_| "ok".to_string())
+}
+
+#[test]
+fn numeric_grammars_accept_zig_spellings() {
+    assert_eq!(parse("window-height", b"0X10").unwrap().window_height, 16);
+    assert_eq!(parse("window-height", b"1__0").unwrap().window_height, 10);
+    assert_eq!(parse("window-height", b"0b1_0").unwrap().window_height, 2);
+    assert_eq!(parse("font-size", b"1_4").unwrap().font_size, 14.0);
+    assert_eq!(parse("font-size", b"0x1.cp+3").unwrap().font_size, 14.0);
+    assert_eq!(
+        parse("window-padding-x", b"1_0")
+            .unwrap()
+            .window_padding_x
+            .top_left,
+        10
+    );
+    assert_eq!(kind("window-padding-x", b"0x10"), "InvalidValue");
+    assert_eq!(kind("window-height", b"1_"), "InvalidValue");
+    assert_eq!(kind("font-size", b"1__0"), "InvalidValue");
+    // Decimal-only places keep rejecting prefixes.
+    assert_eq!(kind("adjust-cell-width", b"0x10"), "InvalidFormat");
+    assert_eq!(kind("adjust-cell-width", b"1_0"), "ok");
+    assert_eq!(kind("adjust-cell-width", b"0x1p3%"), "ok");
+    assert_eq!(kind("quick-terminal-size", b"1_0px"), "ok");
+    assert_eq!(kind("quick-terminal-size", b"0x1p3%,1_0px"), "ok");
+    assert_eq!(kind("quick-terminal-size", b"0x10px"), "InvalidValue");
+    assert_eq!(kind("font-variation", b"wght=1_0.5"), "ok");
+    assert_eq!(kind("font-variation", b"wght=0x1p4"), "ok");
+    assert_eq!(kind("mouse-scroll-multiplier", b"1_0"), "ok");
+    assert_eq!(kind("palette", b"0x10=#fff"), "ok");
+    assert_eq!(kind("palette", b"256=#fff"), "Overflow");
+    assert_eq!(kind("palette", b"-1=#fff"), "Overflow");
+    assert_eq!(kind("palette", b"-0=#fff"), "ok");
+    assert_eq!(kind("palette", b"1x=#fff"), "InvalidCharacter");
+    assert_eq!(kind("background-blur", b"0b11"), "ok");
+    assert_eq!(kind("keybind", b"a=scroll_page_lines:1_0"), "ok");
+    assert_eq!(
+        kind("keybind", b"a=scroll_page_lines:0x10"),
+        "InvalidFormat"
+    );
+    assert_eq!(kind("keybind", b"a=set_font_size:1_4"), "ok");
+    assert_eq!(kind("keybind", b"a=set_font_size:0x1.cp+3"), "ok");
+    assert_eq!(kind("keybind", b"a=resize_split:up,1_0"), "ok");
+    assert_eq!(kind("keybind", b"a=goto_tab:1__0"), "ok");
+    assert_eq!(kind("keybind", b"a=goto_tab:_1"), "InvalidFormat");
+}
+
+#[test]
+fn invalid_bytes_keep_field_specific_error_kinds() {
+    for key in [
+        "adjust-cell-width",
+        "adjust-cursor-height",
+        "adjust-icon-height",
+    ] {
+        assert_eq!(kind(key, b"\xff"), "InvalidFormat", "{key}");
+        assert_eq!(kind(key, b"10px\xff"), "InvalidFormat", "{key}");
+        assert_eq!(kind(key, b"\xff%"), "InvalidFormat", "{key}");
+    }
+    assert_eq!(kind("quick-terminal-size", b"\xff"), "MissingUnit");
+    assert_eq!(kind("quick-terminal-size", b"a\xffb"), "MissingUnit");
+    assert_eq!(kind("quick-terminal-size", b"\xff%"), "InvalidValue");
+    assert_eq!(kind("quick-terminal-size", b"1px,\xff"), "MissingUnit");
+    assert_eq!(kind("link", b"\xff"), "NotImplemented");
+    assert_eq!(kind("link", b"x"), "NotImplemented");
+    for key in [
+        "background",
+        "foreground",
+        "cursor-color",
+        "bold-color",
+        "split-divider-color",
+    ] {
+        assert_eq!(kind(key, b"a\xffb"), "InvalidCharacter", "{key}");
+        assert_eq!(kind(key, b"\xff"), "InvalidValue", "{key}");
+    }
+    assert_eq!(kind("palette", b"1=a\xffb"), "InvalidCharacter");
+    assert_eq!(kind("palette", b"1=\xff"), "InvalidValue");
+    assert_eq!(kind("keybind", b"\xff=a"), "InvalidAction");
+    assert_eq!(kind("keybind", b"\xff=ignore"), "InvalidFormat");
+    assert_eq!(kind("keybind", b"ctrl+a=goto_tab:\xff"), "InvalidFormat");
+    assert_eq!(kind("keybind", b"ctrl+a=nope:\xff"), "InvalidAction");
+    assert_eq!(kind("keybind", b"ctrl+a=text:\xff"), "ok");
+}
+
+#[test]
+fn failed_background_blur_parse_leaves_a_zero_radius_like_zig() {
+    use ghostty_config::types_b::BackgroundBlur;
+    let mut config = Config::default();
+    assert!(
+        config
+            .parse_field_bytes("background-blur", Some(b"bad"))
+            .is_err()
+    );
+    assert_eq!(config.background_blur, BackgroundBlur::Radius(0));
+    config
+        .parse_field_bytes("background-blur", Some(b"7"))
+        .unwrap();
+    assert!(
+        config
+            .parse_field_bytes("background-blur", Some(b"\xff"))
+            .is_err()
+    );
+    assert_eq!(config.background_blur, BackgroundBlur::Radius(7));
+}
+
+#[test]
+fn float_nan_formats_like_zig_and_finalize_clamps_like_zig() {
+    let mut config = parse("font-size", b"nan").unwrap();
+    let mut out = String::new();
+    ghostty_config::formatter::format_entry("font-size", &config.font_size, &mut out).unwrap();
+    assert_eq!(out, "font-size = nan\n");
+
+    config
+        .parse_field_bytes("faint-opacity", Some(b"nan"))
+        .unwrap();
+    config
+        .parse_field_bytes("unfocused-split-opacity", Some(b"nan"))
+        .unwrap();
+    config
+        .parse_field_bytes("minimum-contrast", Some(b"nan"))
+        .unwrap();
+    config
+        .parse_field_bytes("mouse-scroll-multiplier", Some(b"nan"))
+        .unwrap();
+    config.finalize().unwrap();
+    assert_eq!(config.faint_opacity, 1.0);
+    assert_eq!(config.unfocused_split_opacity, 0.15);
+    assert_eq!(config.minimum_contrast, 1.0);
+    assert_eq!(config.mouse_scroll_multiplier.precision, 0.01);
+
+    let mut config = parse("faint-opacity", b"-0").unwrap();
+    config.finalize().unwrap();
+    assert!(config.faint_opacity.is_sign_positive());
+}
diff --git a/crates/ghostty-font/src/discovery.rs b/crates/ghostty-font/src/discovery.rs
index c72e4f6..ccb1559 100644
--- a/crates/ghostty-font/src/discovery.rs
+++ b/crates/ghostty-font/src/discovery.rs
@@ -162,6 +162,43 @@ mod fc_impl {
 mod tests {
     use super::*;
 
+    #[cfg(font_fontconfig)]
+    #[test]
+    fn interior_nul_in_font_names_ends_the_c_string() {
+        use ghostty_config::config::Config;
+        use ghostty_os::osbytes::os_bytes;
+
+        use crate::fontconfig::Property;
+        let mut config = Config::default();
+        config
+            .parse_field_bytes("font-family", Some(b"monospace\0suffix"))
+            .unwrap();
+        config
+            .parse_field_bytes("font-style", Some(b"Regular\0suffix"))
+            .unwrap();
+        config
+            .parse_field_bytes("font-codepoint-map", Some(b"U+0041=Fam\0ily"))
+            .unwrap();
+        let pat = to_fc_pattern(&Descriptor {
+            family: Some(config.font_family.list[0].clone()),
+            style: config.font_style.name_value().cloned(),
+            ..Descriptor::default()
+        });
+        assert_eq!(
+            os_bytes(&pat.get_os_string(Property::Family, 0).unwrap()),
+            b"monospace"
+        );
+        assert_eq!(
+            os_bytes(&pat.get_os_string(Property::Style, 0).unwrap()),
+            b"Regular"
+        );
+        let pat = to_fc_pattern(&config.font_codepoint_map.map.list[0].descriptor);
+        assert_eq!(
+            os_bytes(&pat.get_os_string(Property::Family, 0).unwrap()),
+            b"Fam"
+        );
+    }
+
     #[cfg(font_fontconfig)]
     #[test]
     fn configured_font_names_reach_fontconfig_as_original_bytes() {
diff --git a/crates/ghostty-font/src/fontconfig.rs b/crates/ghostty-font/src/fontconfig.rs
index 362ab40..b507b76 100644
--- a/crates/ghostty-font/src/fontconfig.rs
+++ b/crates/ghostty-font/src/fontconfig.rs
@@ -189,8 +189,10 @@ impl Pattern {
         self.add_string_bytes(prop, v.as_bytes())
     }
 
-    /// [`Pattern::add_string`] for arbitrary bytes (file names).
+    /// [`Pattern::add_string`] for arbitrary bytes (file names). Like Zig's
+    /// sentinel-terminated C string handoff, the value ends at the first NUL.
     pub fn add_string_bytes(&mut self, prop: Property, v: &[u8]) -> bool {
+        let v = v.split(|&b| b == 0).next().unwrap_or(v);
         let Ok(c) = CString::new(v) else {
             return false;
         };
diff --git a/crates/ghostty-input/src/binding/action.rs b/crates/ghostty-input/src/binding/action.rs
index 1c8813f..075961c 100644
--- a/crates/ghostty-input/src/binding/action.rs
+++ b/crates/ghostty-input/src/binding/action.rs
@@ -177,10 +177,8 @@ impl SplitResizeParameter {
     pub(super) fn parse_param(param: &str) -> Result<SplitResizeParameter, Error> {
         let mut it = param.split(',');
         let dir = SplitResizeDirection::parse_param(it.next().ok_or(Error::InvalidFormat)?)?;
-        let amt = it
-            .next()
-            .ok_or(Error::InvalidFormat)?
-            .parse::<u16>()
+        let amt = it.next().ok_or(Error::InvalidFormat)?;
+        let amt = ghostty_os::zig_fmt::parse_int::<u16>(amt.as_bytes(), 10)
             .map_err(|_| Error::InvalidFormat)?;
         // If we have extra parameters it is an error
         if it.next().is_some() {
@@ -304,16 +302,23 @@ pub(super) trait ParseNum: Sized {
     fn parse_param(s: &str) -> Result<Self, Error>;
 }
 
-macro_rules! num_param {
+macro_rules! int_param {
     ($($t:ty),*) => {$(
         impl ParseNum for $t {
             fn parse_param(s: &str) -> Result<$t, Error> {
-                s.parse::<$t>().map_err(|_| Error::InvalidFormat)
+                ghostty_os::zig_fmt::parse_int::<$t>(s.as_bytes(), 10)
+                    .map_err(|_| Error::InvalidFormat)
             }
         }
     )*};
 }
-num_param!(f32, usize, isize, i16);
+int_param!(usize, isize, i16);
+
+impl ParseNum for f32 {
+    fn parse_param(s: &str) -> Result<f32, Error> {
+        ghostty_os::zig_fmt::parse_float::<f32>(s.as_bytes()).map_err(|_| Error::InvalidFormat)
+    }
+}
 
 /// Escape in the style of Zig's `std.zig.stringEscape`.
 pub(super) fn string_escape(s: &[u8], out: &mut String) {
@@ -378,12 +383,14 @@ impl Action {
             "set_tab_title" => Ok(Self::SetTabTitle(bytes()?)),
             "activate_key_table" => Ok(Self::ActivateKeyTable(bytes()?)),
             "activate_key_table_once" => Ok(Self::ActivateKeyTableOnce(bytes()?)),
+            // Zig never validates UTF-8 for enum/numeric parameters: the
+            // bytes just fail the field's own grammar (`InvalidFormat`) for
+            // a known action and `InvalidAction` for an unknown name. U+FFFD
+            // is accepted by none of those grammars, so it stands in for any
+            // invalid parameter.
             _ => Self::parse_named(
                 name,
-                param
-                    .map(std::str::from_utf8)
-                    .transpose()
-                    .map_err(|_| Error::InvalidAction)?,
+                param.map(|p| std::str::from_utf8(p).unwrap_or("\u{fffd}")),
             ),
         }
     }
@@ -1930,15 +1937,15 @@ impl Action {
             }
             Action::IncreaseFontSize(v) => {
                 out.push(':');
-                out.push_str(&v.to_string());
+                out.push_str(&ghostty_os::zig_fmt::format_float_d(*v));
             }
             Action::DecreaseFontSize(v) => {
                 out.push(':');
-                out.push_str(&v.to_string());
+                out.push_str(&ghostty_os::zig_fmt::format_float_d(*v));
             }
             Action::SetFontSize(v) => {
                 out.push(':');
-                out.push_str(&v.to_string());
+                out.push_str(&ghostty_os::zig_fmt::format_float_d(*v));
             }
             Action::Search(v) => {
                 out.push(':');
@@ -1954,7 +1961,7 @@ impl Action {
             }
             Action::ScrollPageFractional(v) => {
                 out.push(':');
-                out.push_str(&v.to_string());
+                out.push_str(&ghostty_os::zig_fmt::format_float_d(*v));
             }
             Action::ScrollPageLines(v) => {
                 out.push(':');
diff --git a/crates/ghostty-input/src/binding/mod.rs b/crates/ghostty-input/src/binding/mod.rs
index 91e78a8..e670170 100644
--- a/crates/ghostty-input/src/binding/mod.rs
+++ b/crates/ghostty-input/src/binding/mod.rs
@@ -173,11 +173,7 @@ impl<'a> Parser<'a> {
                 // This is kind of hacky but we put a dummy trigger
                 // for chained inputs. The `next` will never yield this
                 // because we have chain set.
-                input: if chain {
-                    "a"
-                } else {
-                    std::str::from_utf8(&input[..eql_idx]).map_err(|_| Error::InvalidFormat)?
-                },
+                input: if chain { b"a" } else { &input[..eql_idx] },
                 i: 0,
             },
             action: Action::parse_bytes(&input[eql_idx + 1..])?,
@@ -279,13 +275,16 @@ pub struct SequenceIterator<'a> {
     /// The input of triggers. This is expected to be ONLY triggers. Things
     /// like the "unconsumed:" prefix or action must be stripped before
     /// passing to this iterator.
-    pub input: &'a str,
+    pub input: &'a [u8],
     pub i: usize,
 }
 
 impl<'a> SequenceIterator<'a> {
     pub fn new(input: &'a str) -> Self {
-        SequenceIterator { input, i: 0 }
+        SequenceIterator {
+            input: input.as_bytes(),
+            i: 0,
+        }
     }
 
     /// Returns the next trigger in the sequence if there is no parsing error.
@@ -294,9 +293,9 @@ impl<'a> SequenceIterator<'a> {
             return Ok(None);
         }
         let rem = &self.input[self.i..];
-        let idx = rem.find('>').unwrap_or(rem.len());
+        let idx = rem.iter().position(|b| *b == b'>').unwrap_or(rem.len());
         self.i += idx + 1;
-        Ok(Some(Trigger::parse(&rem[..idx])?))
+        Ok(Some(Trigger::parse_bytes(&rem[..idx])?))
     }
 
     /// Returns true if there are no more triggers to parse.
@@ -545,19 +544,28 @@ impl Trigger {
     /// not be part of a sequence (i.e. `a>b`). This parses exactly a single
     /// trigger.
     pub fn parse(input: &str) -> Result<Trigger, Error> {
+        Trigger::parse_bytes(input.as_bytes())
+    }
+
+    /// [`Trigger::parse`] over the original bytes. Invalid UTF-8 can only
+    /// reach (and fail) the key lookups, which all end in `InvalidFormat`.
+    pub fn parse_bytes(input: &[u8]) -> Result<Trigger, Error> {
         if input.is_empty() {
             return Err(Error::InvalidFormat);
         }
         let mut result = Trigger::default();
-        let mut rem: &str = input;
+        let mut rem: &[u8] = input;
         'outer: while !rem.is_empty() {
-            let idx = rem.find('+').unwrap_or(rem.len());
+            let idx = rem.iter().position(|b| *b == b'+').unwrap_or(rem.len());
             let part = &rem[..idx];
             rem = if idx >= rem.len() {
-                ""
+                b""
             } else {
                 &rem[idx + 1..]
             };
+            let Ok(part) = std::str::from_utf8(part) else {
+                return Err(Error::InvalidFormat);
+            };
 
             // Check if its a modifier
             {
diff --git a/crates/ghostty-lib/src/action_c.rs b/crates/ghostty-lib/src/action_c.rs
index 363e293..86df4b8 100644
--- a/crates/ghostty-lib/src/action_c.rs
+++ b/crates/ghostty-lib/src/action_c.rs
@@ -34,16 +34,15 @@ pub struct Keep {
 }
 
 impl Keep {
-    /// A NUL terminated copy of `s` (interior NULs are dropped).
+    /// A NUL terminated copy of `s` (it ends at the first interior NUL).
     fn cstr(&mut self, s: &str) -> *const c_char {
         self.cstr_bytes(s.as_bytes())
     }
 
     /// [`Keep::cstr`] for raw bytes.
     fn cstr_bytes(&mut self, s: &[u8]) -> *const c_char {
-        let mut s = s.to_vec();
-        s.retain(|&b| b != 0);
-        let c = CString::new(s).unwrap_or_default();
+        let end = s.iter().position(|&b| b == 0).unwrap_or(s.len());
+        let c = CString::new(&s[..end]).unwrap_or_default();
         let ptr = c.as_ptr();
         // The heap buffer of a CString doesn't move when the Vec grows.
         self.strings.push(c);
@@ -241,6 +240,26 @@ mod tests {
 
     use super::*;
 
+    #[test]
+    fn c_title_actions_end_at_the_first_interior_nul() {
+        use ghostty_os::osbytes::EncodedOs;
+        let mut keep = Keep::default();
+        for tab in [false, true] {
+            let title = SetTitle {
+                title: EncodedOs::from_bytes(b"a\0b"),
+            };
+            let action = if tab {
+                Action::SetTabTitle(title)
+            } else {
+                Action::SetTitle(title)
+            };
+            let c = action_to_c(&action, &mut keep);
+            // SAFETY: both title union members have identical layout, pointer owned by keep.
+            let title = unsafe { std::ffi::CStr::from_ptr(c.action.set_title.title) };
+            assert_eq!(title.to_bytes(), b"a");
+        }
+    }
+
     #[test]
     fn c_title_actions_and_key_table_names_forward_original_bytes() {
         use ghostty_os::osbytes::EncodedOs;
diff --git a/crates/ghostty-lib/src/config_capi.rs b/crates/ghostty-lib/src/config_capi.rs
index 8303589..6deb96a 100644
--- a/crates/ghostty-lib/src/config_capi.rs
+++ b/crates/ghostty-lib/src/config_capi.rs
@@ -98,18 +98,23 @@ impl CConfig {
     }
 }
 
-/// A C string without interior NULs.
+/// A C string over `bytes` that ends at the first NUL, like a C consumer
+/// reading Zig's backing bytes (the rest is never visible through the pointer).
+fn cstring_until_nul(bytes: &[u8]) -> CString {
+    let end = bytes.iter().position(|&b| b == 0).unwrap_or(bytes.len());
+    CString::new(&bytes[..end]).unwrap_or_default()
+}
+
+/// A C string for a UTF-8 string, ending at the first NUL.
 fn cstring(s: &str) -> CString {
-    CString::new(s.replace('\0', "")).unwrap_or_default()
+    cstring_until_nul(s.as_bytes())
 }
 
 /// A C string for a config *value*: config strings carry non-UTF-8 bytes in
 /// the reversible [`ghostty_os::osbytes`] encoding, so the embedder gets the
 /// decoded bytes (Zig hands out the original byte slice).
 fn cstring_value(s: &str) -> CString {
-    let mut bytes = ghostty_os::osbytes::config_str_to_bytes(s);
-    bytes.retain(|b| *b != 0);
-    CString::new(bytes).unwrap_or_default()
+    cstring_until_nul(&ghostty_os::osbytes::config_str_to_bytes(s))
 }
 
 /// Intern a string for the lifetime of the process (enum tag names).
@@ -614,6 +619,23 @@ mod tests {
         assert_eq!(b.strings[0].to_str().unwrap(), "h\u{e9}llo");
     }
 
+    #[test]
+    fn config_string_values_end_at_the_first_interior_nul() {
+        use ghostty_os::osbytes::EncodedOs;
+        let enc = EncodedOs::from_bytes(b"a\0b");
+        let b = build_backing(&CValue::String(enc.into_encoded()));
+        assert_eq!(b.strings[0].as_bytes(), b"a");
+        let b = build_backing(&CValue::String("x\0y".to_owned()));
+        assert_eq!(b.strings[0].as_bytes(), b"x");
+        let enc = EncodedOs::from_bytes(b"\0lead");
+        let b = build_backing(&CValue::Path {
+            path: enc.into_encoded(),
+            optional: false,
+        });
+        assert_eq!(b.strings[0].as_bytes(), b"");
+        assert_eq!(intern("ab\0c"), intern("ab"));
+    }
+
     fn get<T: Copy>(cfg: ghostty_config_t, key: &str, init: T) -> (bool, T) {
         let mut out = init;
         // SAFETY: `out` is a valid destination of the key's C type.
diff --git a/crates/ghostty-lib/src/embedded.rs b/crates/ghostty-lib/src/embedded.rs
index 687dd99..451c63a 100644
--- a/crates/ghostty-lib/src/embedded.rs
+++ b/crates/ghostty-lib/src/embedded.rs
@@ -626,9 +626,8 @@ impl RtSurface for SurfaceRt {
             .iter()
             .map(|(m, d)| {
                 (
-                    CString::new(m.replace('\0', "")).unwrap_or_default(),
-                    CString::new(d.iter().copied().filter(|b| *b != 0).collect::<Vec<u8>>())
-                        .unwrap_or_default(),
+                    nul_terminated_prefix(m.as_bytes()),
+                    nul_terminated_prefix(d),
                 )
             })
             .collect();
@@ -2157,6 +2156,13 @@ mod darwin {
     }
 }
 
+/// A C string that ends at the first interior NUL, like a C consumer of a
+/// Zig sentinel-terminated slice.
+fn nul_terminated_prefix(bytes: &[u8]) -> CString {
+    let end = bytes.iter().position(|&b| b == 0).unwrap_or(bytes.len());
+    CString::new(&bytes[..end]).unwrap_or_default()
+}
+
 #[cfg(test)]
 mod tests {
     use std::os::unix::ffi::OsStrExt;
diff --git a/crates/ghostty-os/src/arg_iterator.rs b/crates/ghostty-os/src/arg_iterator.rs
new file mode 100644
index 0000000..c7bd203
--- /dev/null
+++ b/crates/ghostty-os/src/arg_iterator.rs
@@ -0,0 +1,254 @@
+//! Port of Zig 0.16 `std.process.ArgIteratorGeneral` (`process/Args.zig`).
+//!
+//! Splits a command line on space, tab, CR and LF. Double quotes group;
+//! backslashes are only special before a double quote (or a single quote
+//! when `single_quotes` is enabled). A NUL byte terminates the command line,
+//! exactly like Zig's sentinel handling.
+
+/// `ArgIteratorGeneral` options.
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
+pub struct Options {
+    /// Treat `#` at a token start as a comment up to end of line.
+    pub comments: bool,
+    /// Treat `'` as a quote character.
+    pub single_quotes: bool,
+}
+
+/// Iterator over the arguments of a command line.
+#[derive(Debug, Clone)]
+pub struct ArgIteratorGeneral<'a> {
+    cmd_line: &'a [u8],
+    index: usize,
+    options: Options,
+}
+
+impl<'a> ArgIteratorGeneral<'a> {
+    #[must_use]
+    pub fn new(options: Options, cmd_line: &'a [u8]) -> Self {
+        ArgIteratorGeneral {
+            cmd_line,
+            index: 0,
+            options,
+        }
+    }
+
+    /// The byte at the cursor, or 0 at the end (the sentinel).
+    fn character(&self) -> u8 {
+        self.cmd_line.get(self.index).copied().unwrap_or(0)
+    }
+
+    /// Skips whitespace (and comments). Returns false at the terminator.
+    fn skip_whitespace(&mut self) -> bool {
+        loop {
+            match self.character() {
+                0 => return false,
+                b' ' | b'\t' | b'\r' | b'\n' => {}
+                b'#' => {
+                    if self.options.comments {
+                        loop {
+                            match self.cmd_line.get(self.index).copied().unwrap_or(0) {
+                                b'\n' => break,
+                                0 => return false,
+                                _ => self.index += 1,
+                            }
+                        }
+                        // The loop `continue`s, which advances past the newline.
+                    } else {
+                        break;
+                    }
+                }
+                _ => break,
+            }
+            self.index += 1;
+        }
+        true
+    }
+
+    /// Skips the next argument. Returns false at the end.
+    pub fn skip_arg(&mut self) -> bool {
+        if !self.skip_whitespace() {
+            return false;
+        }
+
+        let mut backslash_count: usize = 0;
+        let mut in_quote = false;
+        loop {
+            let c = self.character();
+            match c {
+                0 => return true,
+                b'"' | b'\'' => {
+                    if !self.options.single_quotes && c == b'\'' {
+                        backslash_count = 0;
+                    } else {
+                        let quote_is_real = backslash_count.is_multiple_of(2);
+                        if quote_is_real {
+                            in_quote = !in_quote;
+                        }
+                    }
+                }
+                b'\\' => backslash_count += 1,
+                b' ' | b'\t' | b'\r' | b'\n' => {
+                    if !in_quote {
+                        return true;
+                    }
+                    backslash_count = 0;
+                }
+                _ => backslash_count = 0,
+            }
+            self.index += 1;
+        }
+    }
+
+    /// The next argument, or `None` at the end.
+    pub fn next_arg(&mut self) -> Option<Vec<u8>> {
+        if !self.skip_whitespace() {
+            return None;
+        }
+
+        let mut out: Vec<u8> = Vec::new();
+        let mut backslash_count: usize = 0;
+        let mut in_quote = false;
+        let emit_backslashes =
+            |out: &mut Vec<u8>, n: usize| out.extend(std::iter::repeat_n(b'\\', n));
+        loop {
+            let c = self.character();
+            match c {
+                0 => {
+                    emit_backslashes(&mut out, backslash_count);
+                    return Some(out);
+                }
+                b'"' | b'\'' => {
+                    if !self.options.single_quotes && c == b'\'' {
+                        emit_backslashes(&mut out, backslash_count);
+                        backslash_count = 0;
+                        out.push(c);
+                    } else {
+                        let quote_is_real = backslash_count.is_multiple_of(2);
+                        emit_backslashes(&mut out, backslash_count / 2);
+                        backslash_count = 0;
+                        if quote_is_real {
+                            in_quote = !in_quote;
+                        } else {
+                            out.push(b'"');
+                        }
+                    }
+                }
+                b'\\' => backslash_count += 1,
+                b' ' | b'\t' | b'\r' | b'\n' => {
+                    emit_backslashes(&mut out, backslash_count);
+                    backslash_count = 0;
+                    if in_quote {
+                        out.push(c);
+                    } else {
+                        return Some(out);
+                    }
+                }
+                _ => {
+                    emit_backslashes(&mut out, backslash_count);
+                    backslash_count = 0;
+                    out.push(c);
+                }
+            }
+            self.index += 1;
+        }
+    }
+}
+
+impl Iterator for ArgIteratorGeneral<'_> {
+    type Item = Vec<u8>;
+
+    fn next(&mut self) -> Option<Vec<u8>> {
+        self.next_arg()
+    }
+}
+
+#[cfg(test)]
+#[allow(clippy::byte_char_slices)]
+mod tests {
+    use super::*;
+
+    fn response_file(input: &str, expected: &[&str]) {
+        let it = ArgIteratorGeneral::new(
+            Options {
+                comments: true,
+                single_quotes: true,
+            },
+            input.as_bytes(),
+        );
+        let got: Vec<Vec<u8>> = it.collect();
+        let want: Vec<Vec<u8>> = expected.iter().map(|s| s.as_bytes().to_vec()).collect();
+        assert_eq!(got, want, "{input:?}");
+    }
+
+    #[test]
+    fn response_file_arg_parsing() {
+        response_file("a b\nc d\\", &["a", "b", "c", "d\\"]);
+        response_file("a b c d\\", &["a", "b", "c", "d\\"]);
+        response_file(
+            "j\n k l # this is a comment \\\\ \\\\\\ \\\\\\\\ \"none\" \"\\\\\" \"\\\\\\\"\n \"m\" #another comment\n",
+            &["j", "k", "l", "m"],
+        );
+        response_file(
+            " \"\" q \"\"\n \"r s # t\" \"u\\\" v\" #another comment\n",
+            &["", "q", "", "r s # t", "u\" v"],
+        );
+        response_file(
+            " -l\"advapi32\" a# b#c d#\ne\\\\\\",
+            &["-ladvapi32", "a#", "b#c", "d#", "e\\\\\\"],
+        );
+        response_file(" 'foo' \"bar\"", &["foo", "bar"]);
+    }
+
+    fn general(input: &[u8]) -> Vec<Vec<u8>> {
+        ArgIteratorGeneral::new(Options::default(), input).collect()
+    }
+
+    #[test]
+    fn all_zig_separators_split() {
+        for sep in [b' ', b'\t', b'\r', b'\n'] {
+            assert_eq!(
+                general(&[b'a', sep, b'b']),
+                vec![b"a".to_vec(), b"b".to_vec()]
+            );
+            assert_eq!(general(&[sep, sep, b'a', sep, sep]), vec![b"a".to_vec()]);
+        }
+        // VT and FF are not separators.
+        assert_eq!(general(b"a\x0bb\x0cc"), vec![b"a\x0bb\x0cc".to_vec()]);
+        // Quoted separators are kept.
+        assert_eq!(
+            general(b"\"a\nb\r\tc\" d"),
+            vec![b"a\nb\r\tc".to_vec(), b"d".to_vec()]
+        );
+    }
+
+    #[test]
+    fn quoting_and_backslash_rules() {
+        assert_eq!(general(b"a\\b"), vec![b"a\\b".to_vec()]);
+        assert_eq!(general(b"\\\\\\\"x"), vec![b"\\\"x".to_vec()]);
+        assert_eq!(general(b"\\\\\"x y\""), vec![b"\\x y".to_vec()]);
+        // Single quotes are ordinary characters by default.
+        assert_eq!(general(b"'a b'"), vec![b"'a".to_vec(), b"b'".to_vec()]);
+        // Unterminated quote runs to the end.
+        assert_eq!(general(b"\"a b"), vec![b"a b".to_vec()]);
+        // Trailing backslashes are emitted verbatim.
+        assert_eq!(general(b"a\\\\"), vec![b"a\\\\".to_vec()]);
+        // Empty quoted argument.
+        assert_eq!(general(b"\"\" x"), vec![b"".to_vec(), b"x".to_vec()]);
+    }
+
+    #[test]
+    fn nul_terminates_the_command_line() {
+        assert_eq!(general(b"a b\0c d"), vec![b"a".to_vec(), b"b".to_vec()]);
+        assert_eq!(general(b"\0a"), Vec::<Vec<u8>>::new());
+        assert_eq!(general(b"\"a\0b\" c"), vec![b"a".to_vec()]);
+    }
+
+    #[test]
+    fn skip_matches_next() {
+        let mut it = ArgIteratorGeneral::new(Options::default(), b"a \"b c\"\nd");
+        assert!(it.skip_arg());
+        assert_eq!(it.next_arg(), Some(b"b c".to_vec()));
+        assert!(it.skip_arg());
+        assert!(!it.skip_arg());
+    }
+}
diff --git a/crates/ghostty-os/src/desktop.rs b/crates/ghostty-os/src/desktop.rs
index 6542a18..fe213d7 100644
--- a/crates/ghostty-os/src/desktop.rs
+++ b/crates/ghostty-os/src/desktop.rs
@@ -33,11 +33,12 @@ pub fn launched_from_desktop() -> bool {
 
     // (`std::process::id` is `getpid` / `GetCurrentProcessId`.)
     let pid = std::process::id();
-    let Ok(gio_pid) = gio_pid_str.to_string_lossy().parse::<u32>() else {
+    // (`parseInt(c_int, ..., 10)`.)
+    let Ok(gio_pid) = crate::zig_fmt::parse_int::<i32>(gio_pid_str.as_encoded_bytes(), 10) else {
         return false;
     };
 
-    gio_pid == pid
+    i64::from(gio_pid) == i64::from(pid)
 }
 
 /// Environment variable set by the macOS app to tell libghostty how it was
diff --git a/crates/ghostty-os/src/lib.rs b/crates/ghostty-os/src/lib.rs
index 59891a2..479f7dd 100644
--- a/crates/ghostty-os/src/lib.rs
+++ b/crates/ghostty-os/src/lib.rs
@@ -14,6 +14,7 @@
     )
 )]
 
+pub mod arg_iterator;
 pub mod args;
 #[cfg(not(target_arch = "wasm32"))]
 pub mod cf_release_thread;
@@ -31,6 +32,7 @@ pub mod file_type;
 #[cfg(unix)]
 pub mod flatpak;
 pub mod osbytes;
+pub mod zig_fmt;
 #[cfg(windows)]
 pub mod flatpak {
     //! Flatpak does not exist on Windows.
diff --git a/crates/ghostty-os/src/osbytes.rs b/crates/ghostty-os/src/osbytes.rs
index 25ca6df..36bda32 100644
--- a/crates/ghostty-os/src/osbytes.rs
+++ b/crates/ghostty-os/src/osbytes.rs
@@ -431,6 +431,17 @@ impl EncodedOs {
         }
     }
 
+    /// [`EncodedOs::to_path`] as a syscall sees it: Zig hands paths to the
+    /// OS as NUL-terminated C strings, so an interior NUL ends the path
+    /// (Rust's `std::fs` would refuse the whole path instead).
+    pub fn to_syscall_path(&self) -> std::io::Result<std::path::PathBuf> {
+        let bytes = self.to_bytes();
+        match bytes.iter().position(|&b| b == 0) {
+            Some(end) => EncodedOs::from_bytes(&bytes[..end]).to_path(),
+            None => self.to_path(),
+        }
+    }
+
     /// Whether the decoded value starts with the given plain prefix.
     #[must_use]
     pub fn starts_with_plain(&self, prefix: &str) -> bool {
@@ -526,6 +537,22 @@ pub fn config_str_to_path(s: &str) -> std::io::Result<std::path::PathBuf> {
 mod tests {
     use super::*;
 
+    #[cfg(unix)]
+    #[test]
+    fn syscall_path_ends_at_the_first_nul() {
+        let e = EncodedOs::from_bytes(b"/a/b\0c");
+        assert_eq!(
+            e.to_syscall_path().unwrap(),
+            std::path::PathBuf::from("/a/b")
+        );
+        let e = EncodedOs::from_bytes(b"/a/\xffb");
+        assert_eq!(e.to_syscall_path().unwrap(), e.to_path().unwrap());
+        assert_eq!(
+            EncodedOs::from_bytes(b"\0x").to_syscall_path().unwrap(),
+            std::path::PathBuf::new()
+        );
+    }
+
     #[test]
     fn windows_paths_fail_with_bad_path_name_instead_of_replacement() {
         let error = windows_path_wide(b"C:\\bad\xff").unwrap_err();
diff --git a/crates/ghostty-os/src/zig_fmt.rs b/crates/ghostty-os/src/zig_fmt.rs
new file mode 100644
index 0000000..7b14cc9
--- /dev/null
+++ b/crates/ghostty-os/src/zig_fmt.rs
@@ -0,0 +1,872 @@
+//! Port of Zig 0.16 `std.fmt.parseInt`, `std.fmt.parseUnsigned` and
+//! `std.fmt.parseFloat` (`fmt.zig`, `fmt/parse_float.zig` and
+//! `fmt/parse_float/{parse,convert_hex,FloatStream}.zig`).
+//!
+//! The grammars are reproduced exactly: underscores, `0b`/`0o`/`0x`
+//! prefixes (both cases, base 0 only), sign rules, hex floats, `inf` /
+//! `infinity` / `nan`. Decimal float values are rounded correctly by the
+//! standard library once the Zig grammar has accepted the input (Zig's
+//! algorithm is also correctly rounded); hex floats follow `convertHex`.
+
+/// `std.fmt.ParseIntError`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ParseIntError {
+    /// The result cannot fit in the type specified.
+    Overflow,
+    /// The input was empty or contained an invalid character.
+    InvalidCharacter,
+}
+
+impl std::fmt::Display for ParseIntError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(match self {
+            ParseIntError::Overflow => "Overflow",
+            ParseIntError::InvalidCharacter => "InvalidCharacter",
+        })
+    }
+}
+
+impl std::error::Error for ParseIntError {}
+
+/// `std.fmt.ParseFloatError`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ParseFloatError;
+
+/// Integer types that can be targeted by [`parse_int`].
+pub trait ZigInt: Sized + Copy {
+    const MIN_I128: i128;
+    const MAX_I128: i128;
+    fn from_i128(v: i128) -> Self;
+}
+
+macro_rules! zig_int {
+    ($($t:ty),*) => {$(
+        impl ZigInt for $t {
+            const MIN_I128: i128 = <$t>::MIN as i128;
+            const MAX_I128: i128 = <$t>::MAX as i128;
+            fn from_i128(v: i128) -> Self {
+                v as $t
+            }
+        }
+    )*};
+}
+zig_int!(u8, u16, u32, u64, usize, i8, i16, i32, i64, isize);
+
+/// `std.fmt.charToDigit`.
+fn char_to_digit(c: u8, base: u8) -> Result<u8, ParseIntError> {
+    let value = match c {
+        b'0'..=b'9' => c - b'0',
+        b'A'..=b'Z' => c - b'A' + 10,
+        b'a'..=b'z' => c - b'a' + 10,
+        _ => return Err(ParseIntError::InvalidCharacter),
+    };
+    if value >= base {
+        return Err(ParseIntError::InvalidCharacter);
+    }
+    Ok(value)
+}
+
+/// `std.fmt.parseInt(T, buf, base)`.
+pub fn parse_int<T: ZigInt>(buf: &[u8], base: u8) -> Result<T, ParseIntError> {
+    match buf.first() {
+        None => Err(ParseIntError::InvalidCharacter),
+        Some(b'+') => parse_int_with_sign(&buf[1..], base, false),
+        Some(b'-') => parse_int_with_sign(&buf[1..], base, true),
+        Some(_) => parse_int_with_sign(buf, base, false),
+    }
+}
+
+/// `std.fmt.parseUnsigned(T, buf, base)` (no sign accepted).
+pub fn parse_unsigned<T: ZigInt>(buf: &[u8], base: u8) -> Result<T, ParseIntError> {
+    parse_int_with_sign(buf, base, false)
+}
+
+fn parse_int_with_sign<T: ZigInt>(
+    buf: &[u8],
+    base: u8,
+    negative: bool,
+) -> Result<T, ParseIntError> {
+    if buf.is_empty() {
+        return Err(ParseIntError::InvalidCharacter);
+    }
+
+    let mut buf_base = base;
+    let mut buf_start = buf;
+    if base == 0 {
+        // Treat is as a decimal number by default.
+        buf_base = 10;
+        // Detect the base by looking at buf prefix.
+        if buf.len() > 2 && buf[0] == b'0' {
+            match buf[1].to_ascii_lowercase() {
+                b'b' => {
+                    buf_base = 2;
+                    buf_start = &buf[2..];
+                }
+                b'o' => {
+                    buf_base = 8;
+                    buf_start = &buf[2..];
+                }
+                b'x' => {
+                    buf_base = 16;
+                    buf_start = &buf[2..];
+                }
+                _ => {}
+            }
+        }
+    }
+
+    if buf_start[0] == b'_' || buf_start[buf_start.len() - 1] == b'_' {
+        return Err(ParseIntError::InvalidCharacter);
+    }
+
+    let mut acc: i128 = 0;
+    for &c in buf_start {
+        if c == b'_' {
+            continue;
+        }
+        let digit = i128::from(char_to_digit(c, buf_base)?);
+        acc = acc
+            .checked_mul(i128::from(buf_base))
+            .ok_or(ParseIntError::Overflow)?;
+        acc = if negative {
+            acc.checked_sub(digit)
+        } else {
+            acc.checked_add(digit)
+        }
+        .ok_or(ParseIntError::Overflow)?;
+        if acc < T::MIN_I128 || acc > T::MAX_I128 {
+            return Err(ParseIntError::Overflow);
+        }
+    }
+    Ok(T::from_i128(acc))
+}
+
+// ---------------------------------------------------------------------
+// Floats
+
+/// Float types that can be targeted by [`parse_float`].
+pub trait ZigFloat: Sized + Copy + std::str::FromStr + std::fmt::Display {
+    fn is_nan_value(self) -> bool;
+    const MANTISSA_BITS: u32;
+    const FRACTIONAL_BITS: u32;
+    const EXP_BITS: u32;
+    const EXP_MAX: i64;
+    const EXP_MIN: i64;
+    const INF: Self;
+    const NAN: Self;
+    fn neg(self) -> Self;
+    fn zero(negative: bool) -> Self;
+    fn from_bits64(bits: u64) -> Self;
+}
+
+macro_rules! zig_float {
+    ($t:ty, $bits:ty, $m:expr, $e:expr, $max:expr, $min:expr) => {
+        impl ZigFloat for $t {
+            const MANTISSA_BITS: u32 = $m;
+            const FRACTIONAL_BITS: u32 = $m;
+            const EXP_BITS: u32 = $e;
+            const EXP_MAX: i64 = $max;
+            const EXP_MIN: i64 = $min;
+            const INF: Self = <$t>::INFINITY;
+            const NAN: Self = <$t>::NAN;
+            fn is_nan_value(self) -> bool {
+                self.is_nan()
+            }
+            fn neg(self) -> Self {
+                -self
+            }
+            fn zero(negative: bool) -> Self {
+                if negative { -0.0 } else { 0.0 }
+            }
+            fn from_bits64(bits: u64) -> Self {
+                <$t>::from_bits(bits as $bits)
+            }
+        }
+    };
+}
+zig_float!(f32, u32, 23, 8, 127, -126);
+zig_float!(f64, u64, 52, 11, 1023, -1022);
+
+struct Number {
+    exponent: i64,
+    mantissa: u64,
+    many_digits: bool,
+    hex: bool,
+}
+
+/// `FloatStream.zig`.
+struct Stream<'a> {
+    slice: &'a [u8],
+    offset: usize,
+    underscore_count: usize,
+}
+
+impl<'a> Stream<'a> {
+    fn new(slice: &'a [u8]) -> Self {
+        Stream {
+            slice,
+            offset: 0,
+            underscore_count: 0,
+        }
+    }
+
+    fn offset_true(&self) -> usize {
+        self.offset - self.underscore_count
+    }
+
+    fn reset(&mut self) {
+        self.offset = 0;
+        self.underscore_count = 0;
+    }
+
+    fn first(&self) -> Option<u8> {
+        self.slice.get(self.offset).copied()
+    }
+
+    fn first_is(&self, cs: &[u8]) -> bool {
+        self.first().is_some_and(|c| cs.contains(&c))
+    }
+
+    fn first_is_lower(&self, c: u8) -> bool {
+        self.first().is_some_and(|ok| ok | 0x20 == c)
+    }
+
+    fn first_is_digit(&self, base: u8) -> bool {
+        self.first().is_some_and(|c| is_digit(c, base))
+    }
+
+    fn advance(&mut self, n: usize) {
+        self.offset += n;
+    }
+
+    fn scan_digit(&mut self, base: u8) -> Option<u8> {
+        loop {
+            let ok = self.first()?;
+            if ok.is_ascii_digit() {
+                self.advance(1);
+                return Some(ok - b'0');
+            } else if base == 16 && (b'a'..=b'f').contains(&ok) {
+                self.advance(1);
+                return Some(ok - b'a' + 10);
+            } else if base == 16 && (b'A'..=b'F').contains(&ok) {
+                self.advance(1);
+                return Some(ok - b'A' + 10);
+            } else if ok == b'_' {
+                self.advance(1);
+                self.underscore_count += 1;
+            } else {
+                return None;
+            }
+        }
+    }
+}
+
+fn is_digit(c: u8, base: u8) -> bool {
+    if base == 10 {
+        c.is_ascii_digit()
+    } else {
+        c.is_ascii_hexdigit()
+    }
+}
+
+fn try_parse_digits(stream: &mut Stream<'_>, x: &mut u64, base: u8) {
+    while let Some(digit) = stream.scan_digit(base) {
+        *x = x
+            .wrapping_mul(u64::from(base))
+            .wrapping_add(u64::from(digit));
+    }
+}
+
+fn min_n_digit_int(digit_count: usize) -> u64 {
+    let mut n: u64 = 1;
+    for _ in 1..digit_count {
+        n = n.wrapping_mul(10);
+    }
+    n
+}
+
+fn try_parse_n_digits(stream: &mut Stream<'_>, x: &mut u64, base: u8, n: usize) {
+    while *x < min_n_digit_int(n) {
+        if let Some(digit) = stream.scan_digit(base) {
+            *x = x
+                .wrapping_mul(u64::from(base))
+                .wrapping_add(u64::from(digit));
+        } else {
+            break;
+        }
+    }
+}
+
+fn parse_scientific(stream: &mut Stream<'_>) -> Option<i64> {
+    let mut exponent: i64 = 0;
+    let mut negative = false;
+
+    if let Some(c) = stream.first() {
+        negative = c == b'-';
+        if c == b'-' || c == b'+' {
+            stream.advance(1);
+        }
+    }
+    if stream.first_is_digit(10) {
+        while let Some(digit) = stream.scan_digit(10) {
+            // no overflows here, saturate well before overflow
+            if exponent < 0x1000_0000 {
+                exponent = 10 * exponent + i64::from(digit);
+            }
+        }
+        return Some(if negative { -exponent } else { exponent });
+    }
+    None
+}
+
+fn valid_underscores(s: &[u8], base: u8) -> bool {
+    let mut i = 0;
+    while i < s.len() {
+        if s[i] == b'_' {
+            // underscore at start of end
+            if i == 0 || i + 1 == s.len() {
+                return false;
+            }
+            // consecutive underscores
+            if !is_digit(s[i - 1], base) || !is_digit(s[i + 1], base) {
+                return false;
+            }
+            // next is guaranteed a digit, skip an extra
+            i += 1;
+        }
+        i += 1;
+    }
+    true
+}
+
+fn parse_partial_number_base(
+    stream: &mut Stream<'_>,
+    n: &mut usize,
+    base: u8,
+    max_mantissa_digits: usize,
+    exp_char_lower: u8,
+) -> Option<Number> {
+    // parse initial digits before dot
+    let mut mantissa: u64 = 0;
+    try_parse_digits(stream, &mut mantissa, base);
+    let int_end = stream.offset_true();
+    let mut n_digits = stream.offset_true() as isize;
+
+    // handle dot with the following digits
+    let mut exponent: i64 = 0;
+    if stream.first_is(b".") {
+        stream.advance(1);
+        let marker = stream.offset_true();
+        try_parse_digits(stream, &mut mantissa, base);
+        let n_after_dot = stream.offset_true() - marker;
+        exponent = -(n_after_dot as i64);
+        n_digits += n_after_dot as isize;
+    }
+
+    // adjust required shift to offset mantissa for base-16 (2^4)
+    if base == 16 {
+        exponent *= 4;
+    }
+
+    if n_digits == 0 {
+        return None;
+    }
+
+    // handle scientific format
+    let mut exp_number: i64 = 0;
+    if stream.first_is_lower(exp_char_lower) {
+        stream.advance(1);
+        exp_number = parse_scientific(stream)?;
+        exponent += exp_number;
+    }
+
+    // length must be complete parsed length
+    *n += stream.offset;
+
+    if stream.underscore_count > 0 && !valid_underscores(stream.slice, base) {
+        return None;
+    }
+
+    // common case with not many digits
+    if n_digits <= max_mantissa_digits as isize {
+        return Some(Number {
+            exponent,
+            mantissa,
+            many_digits: false,
+            hex: base == 16,
+        });
+    }
+
+    n_digits -= max_mantissa_digits as isize;
+    let mut many_digits = false;
+    stream.reset(); // re-parse from beginning
+    while stream.first_is(b"0._") {
+        let next = stream.first().unwrap_or(0);
+        if next == b'_' {
+            stream.underscore_count += 1;
+        } else {
+            n_digits -= isize::from(next.saturating_sub(b'0' - 1));
+        }
+        stream.advance(1);
+    }
+    if n_digits > 0 {
+        // at this point we have more than max_mantissa_digits significant digits
+        many_digits = true;
+        mantissa = 0;
+        stream.reset();
+        try_parse_n_digits(stream, &mut mantissa, base, max_mantissa_digits);
+
+        exponent = if mantissa >= min_n_digit_int(max_mantissa_digits) {
+            // big int
+            int_end as i64 - stream.offset_true() as i64
+        } else {
+            // the next byte must be present and be '.'
+            stream.advance(1);
+            let marker = stream.offset_true();
+            try_parse_n_digits(stream, &mut mantissa, base, max_mantissa_digits);
+            marker as i64 - stream.offset_true() as i64
+        };
+        if base == 16 {
+            exponent *= 4;
+        }
+        // add back the explicit part
+        exponent += exp_number;
+    }
+
+    Some(Number {
+        exponent,
+        mantissa,
+        many_digits,
+        hex: base == 16,
+    })
+}
+
+/// Returns the parsed hex-float `Number`, or a validated decimal slice.
+enum Parsed {
+    Hex(Number),
+    Decimal,
+}
+
+fn parse_number(s: &[u8]) -> Option<Parsed> {
+    let mut consumed: usize = 0;
+    let parsed = if s.len() >= 2 && s[0] == b'0' && s[1].eq_ignore_ascii_case(&b'x') {
+        let mut stream = Stream::new(&s[2..]);
+        consumed += 2;
+        parse_partial_number_base(&mut stream, &mut consumed, 16, 16, b'p').map(Parsed::Hex)
+    } else {
+        let mut stream = Stream::new(s);
+        parse_partial_number_base(&mut stream, &mut consumed, 10, 19, b'e').map(|_| Parsed::Decimal)
+    };
+    // must consume entire float (no trailing data)
+    if s.len() == consumed { parsed } else { None }
+}
+
+fn parse_inf_or_nan<T: ZigFloat>(s: &[u8], negative: bool) -> Option<T> {
+    let starts = |s: &[u8], p: &[u8]| s.len() >= p.len() && s[..p.len()].eq_ignore_ascii_case(p);
+    if starts(s, b"inf") {
+        let consumed = if starts(&s[3..], b"inity") { 8 } else { 3 };
+        if s.len() != consumed {
+            return None;
+        }
+        return Some(if negative { T::INF.neg() } else { T::INF });
+    }
+    if starts(s, b"nan") {
+        return (s.len() == 3).then_some(T::NAN);
+    }
+    None
+}
+
+/// `convert_hex.zig`.
+fn convert_hex<T: ZigFloat>(n_: &Number, negative: bool) -> T {
+    let mut mantissa = n_.mantissa;
+    let mut exponent = n_.exponent;
+
+    if mantissa == 0 {
+        return T::zero(negative);
+    }
+
+    let max_exp = T::EXP_MAX;
+    let min_exp = T::EXP_MIN;
+    let mantissa_bits = T::MANTISSA_BITS;
+    let fractional_bits = T::FRACTIONAL_BITS;
+    let exp_bits = T::EXP_BITS;
+    let exp_bias = min_exp - 1;
+
+    // mantissa now implicitly divided by 2^fractional_bits
+    exponent += i64::from(fractional_bits);
+
+    while mantissa != 0 && mantissa >> (mantissa_bits + 2) == 0 {
+        mantissa <<= 1;
+        exponent -= 1;
+    }
+    if n_.many_digits {
+        mantissa |= 1;
+    }
+    while mantissa >> (1 + fractional_bits + 2) != 0 {
+        mantissa = (mantissa >> 1) | (mantissa & 1);
+        exponent += 1;
+    }
+
+    // If exponent is too negative, denormalize in hopes of making it
+    // representable. (The -2 is for the rounding bits.)
+    while mantissa > 1 && exponent < min_exp - 2 {
+        mantissa = (mantissa >> 1) | (mantissa & 1);
+        exponent += 1;
+    }
+
+    // Round using two bottom bits.
+    let mut round = mantissa & 3;
+    mantissa >>= 2;
+    round |= mantissa & 1; // round to even (round up if mantissa is odd)
+    exponent += 2;
+    if round == 3 {
+        mantissa += 1;
+        if mantissa == 1 << (1 + fractional_bits) {
+            mantissa >>= 1;
+            exponent += 1;
+        }
+    }
+
+    // Denormal or zero
+    if mantissa >> fractional_bits == 0 {
+        exponent = exp_bias;
+    }
+
+    // Infinity and range error
+    if exponent > max_exp {
+        return if negative { T::INF.neg() } else { T::INF };
+    }
+
+    let mut bits = mantissa & ((1u64 << mantissa_bits) - 1);
+    bits |= (((exponent - exp_bias) as u64) & ((1u64 << exp_bits) - 1)) << mantissa_bits;
+    if negative {
+        bits |= 1u64 << (mantissa_bits + exp_bits);
+    }
+    T::from_bits64(bits)
+}
+
+/// Zig's `{d}` for floats: like Rust's `Display` except NaN is `nan`
+/// (infinities are `inf` / `-inf` in both).
+#[must_use]
+pub fn format_float_d<T: ZigFloat>(v: T) -> String {
+    if v.is_nan_value() {
+        "nan".to_string()
+    } else {
+        v.to_string()
+    }
+}
+
+/// `std.fmt.parseFloat(T, s)`.
+pub fn parse_float<T: ZigFloat>(s: &[u8]) -> Result<T, ParseFloatError> {
+    if s.is_empty() {
+        return Err(ParseFloatError);
+    }
+
+    let mut i = 0;
+    let negative = s[i] == b'-';
+    if s[i] == b'-' || s[i] == b'+' {
+        i += 1;
+    }
+    if s.len() == i {
+        return Err(ParseFloatError);
+    }
+    let s = &s[i..];
+
+    match parse_number(s) {
+        None => parse_inf_or_nan::<T>(s, negative).ok_or(ParseFloatError),
+        Some(Parsed::Hex(n)) => {
+            debug_assert!(n.hex);
+            Ok(convert_hex::<T>(&n, negative))
+        }
+        Some(Parsed::Decimal) => {
+            // The grammar is validated; underscores are ignorable now.
+            let cleaned: String = s
+                .iter()
+                .filter(|&&c| c != b'_')
+                .map(|&c| char::from(c))
+                .collect();
+            let v: T = cleaned.parse().map_err(|_| ParseFloatError)?;
+            Ok(if negative { v.neg() } else { v })
+        }
+    }
+}
+
+#[cfg(test)]
+#[allow(clippy::approx_constant)]
+mod tests {
+    use super::*;
+
+    fn pi<T: ZigInt>(s: &str, base: u8) -> Result<T, ParseIntError> {
+        parse_int::<T>(s.as_bytes(), base)
+    }
+
+    #[test]
+    fn parse_int_zig_std_test() {
+        assert_eq!(pi::<i32>("-10", 10), Ok(-10));
+        assert_eq!(pi::<i32>("+10", 10), Ok(10));
+        assert_eq!(pi::<u32>("+10", 10), Ok(10));
+        assert_eq!(pi::<u32>("-10", 10), Err(ParseIntError::Overflow));
+        for bad in [" 10", "10 ", "_10_", "0x_10_", "0x10_", "0x_10"] {
+            assert_eq!(pi::<u32>(bad, 10), Err(ParseIntError::InvalidCharacter));
+        }
+        assert_eq!(pi::<u8>("255", 10), Ok(255));
+        assert_eq!(pi::<u8>("256", 10), Err(ParseIntError::Overflow));
+
+        // +0 and -0 should work for unsigned
+        assert_eq!(pi::<u8>("-0", 10), Ok(0));
+        assert_eq!(pi::<u8>("+0", 10), Ok(0));
+
+        assert_eq!(pi::<i8>("-128", 10), Ok(-128));
+        assert_eq!(pi::<i64>("-4398046511104", 10), Ok(-4_398_046_511_104));
+
+        // empty string or bare +- is invalid
+        for bad in ["", "+", "-"] {
+            assert_eq!(pi::<u32>(bad, 10), Err(ParseIntError::InvalidCharacter));
+            assert_eq!(pi::<i32>(bad, 10), Err(ParseIntError::InvalidCharacter));
+        }
+
+        // autodectect the base
+        assert_eq!(pi::<i32>("111", 0), Ok(111));
+        assert_eq!(pi::<i32>("1_1_1", 0), Ok(111));
+        assert_eq!(pi::<i32>("+0b111", 0), Ok(7));
+        assert_eq!(pi::<i32>("+0B111", 0), Ok(7));
+        assert_eq!(pi::<i32>("+0b1_11", 0), Ok(7));
+        assert_eq!(pi::<i32>("+0o111", 0), Ok(73));
+        assert_eq!(pi::<i32>("+0O111", 0), Ok(73));
+        assert_eq!(pi::<i32>("+0o11_1", 0), Ok(73));
+        assert_eq!(pi::<i32>("+0x111", 0), Ok(273));
+        assert_eq!(pi::<i32>("-0b111", 0), Ok(-7));
+        assert_eq!(pi::<i32>("-0b11_1", 0), Ok(-7));
+        assert_eq!(pi::<i32>("-0o111", 0), Ok(-73));
+        assert_eq!(pi::<i32>("-0x111", 0), Ok(-273));
+        assert_eq!(pi::<i32>("-0X111", 0), Ok(-273));
+        assert_eq!(pi::<i32>("-0x1_11", 0), Ok(-273));
+
+        // bare binary/octal/decimal prefix is invalid
+        for bad in ["0b", "0o", "0x"] {
+            assert_eq!(pi::<u32>(bad, 0), Err(ParseIntError::InvalidCharacter));
+        }
+
+        assert_eq!(pi::<i8>("-10", 2), Ok(-2));
+        assert_eq!(pi::<i8>("-10", 8), Ok(-8));
+        assert_eq!(pi::<i8>("-10", 16), Ok(-16));
+    }
+
+    #[test]
+    fn parse_unsigned_zig_std_test() {
+        let pu = |s: &str, b| parse_unsigned::<u64>(s.as_bytes(), b);
+        assert_eq!(parse_unsigned::<u16>(b"050124", 10), Ok(50124));
+        assert_eq!(parse_unsigned::<u16>(b"65535", 10), Ok(65535));
+        assert_eq!(parse_unsigned::<u16>(b"65_535", 10), Ok(65535));
+        assert_eq!(
+            parse_unsigned::<u16>(b"65536", 10),
+            Err(ParseIntError::Overflow)
+        );
+        assert_eq!(pu("0ffffffffffffffff", 16), Ok(u64::MAX));
+        assert_eq!(pu("0f_fff_fff_fff_fff_fff", 16), Ok(u64::MAX));
+        assert_eq!(pu("10000000000000000", 16), Err(ParseIntError::Overflow));
+        assert_eq!(parse_unsigned::<u32>(b"DeadBeef", 16), Ok(0xDEAD_BEEF));
+        assert_eq!(
+            parse_unsigned::<u32>(b"f", 10),
+            Err(ParseIntError::InvalidCharacter)
+        );
+        assert_eq!(
+            parse_unsigned::<u8>(b"109", 8),
+            Err(ParseIntError::InvalidCharacter)
+        );
+        assert_eq!(parse_unsigned::<u32>(b"NUMBER", 36), Ok(1_442_151_747));
+        // parseUnsigned does not expect a sign
+        assert_eq!(
+            parse_unsigned::<u8>(b"+0", 10),
+            Err(ParseIntError::InvalidCharacter)
+        );
+        assert_eq!(
+            parse_unsigned::<u8>(b"-0", 10),
+            Err(ParseIntError::InvalidCharacter)
+        );
+        assert_eq!(
+            parse_unsigned::<u8>(b"", 10),
+            Err(ParseIntError::InvalidCharacter)
+        );
+    }
+
+    #[test]
+    fn parse_int_non_ascii_and_prefix_edge_cases() {
+        // `buf.len > 2` gates prefix detection: "0x" alone is decimal "0x".
+        assert_eq!(pi::<u32>("0x1", 0), Ok(1));
+        assert_eq!(pi::<u32>("0_1", 0), Ok(1));
+        assert_eq!(pi::<u32>("1__0", 0), Ok(10));
+        assert_eq!(pi::<u32>("0X10", 0), Ok(16));
+        assert_eq!(
+            parse_int::<u32>("é1".as_bytes(), 0),
+            Err(ParseIntError::InvalidCharacter)
+        );
+        // Prefixes are only honoured with base 0.
+        assert_eq!(pi::<u32>("0x10", 10), Err(ParseIntError::InvalidCharacter));
+        assert_eq!(pi::<u32>("0b11", 16), Ok(0xb11));
+    }
+
+    fn pf64(s: &str) -> Result<f64, ParseFloatError> {
+        parse_float::<f64>(s.as_bytes())
+    }
+    fn pf32(s: &str) -> Result<f32, ParseFloatError> {
+        parse_float::<f32>(s.as_bytes())
+    }
+
+    fn approx(a: f64, b: f64) -> bool {
+        (a - b).abs() < 1e-7
+    }
+
+    #[test]
+    fn parse_float_zig_std_test() {
+        for bad in ["", "   1", "1abc", "+", "-"] {
+            assert!(pf64(bad).is_err(), "{bad:?}");
+            assert!(pf32(bad).is_err(), "{bad:?}");
+        }
+        assert_eq!(pf64("0"), Ok(0.0));
+        assert_eq!(pf64("+0"), Ok(0.0));
+        assert_eq!(pf64("-0"), Ok(0.0));
+        assert!(pf64("-0").unwrap().is_sign_negative());
+        assert_eq!(pf64("0e0"), Ok(0.0));
+        assert_eq!(pf64("2e3"), Ok(2000.0));
+        assert_eq!(pf64("1e0"), Ok(1.0));
+        assert_eq!(pf64("-2e3"), Ok(-2000.0));
+        assert_eq!(pf64("-1e0"), Ok(-1.0));
+        assert_eq!(pf64("1.234e3"), Ok(1234.0));
+        assert!(approx(pf64("3.141").unwrap(), 3.141));
+        assert!(approx(pf64("-3.141").unwrap(), -3.141));
+        assert_eq!(pf64("1e-5000"), Ok(0.0));
+        assert_eq!(pf64("1e+5000"), Ok(f64::INFINITY));
+        assert_eq!(
+            pf64("0.4e0066999999999999999999999999999999999999999999999999999"),
+            Ok(f64::INFINITY)
+        );
+        assert!(approx(
+            pf64("0_1_2_3_4_5_6.7_8_9_0_0_0e0_0_1_0").unwrap() / 1e10,
+            123_456.789
+        ));
+        // underscore rule: only between two digits, never repeated.
+        for bad in [
+            "0123456.789000e_0010",
+            "_0123456.789000e0010",
+            "0__123456.789000e_0010",
+            "0123456_.789000e0010",
+            "0123456.789000e0010_",
+        ] {
+            assert!(pf64(bad).is_err(), "{bad:?}");
+        }
+        assert!(approx(pf64("1e-2").unwrap(), 0.01));
+        assert!(approx(pf64("1234e-2").unwrap(), 12.34));
+        assert!(approx(pf64("1.").unwrap(), 1.0));
+        assert!(approx(pf64("0.").unwrap(), 0.0));
+        assert!(approx(pf64(".1").unwrap(), 0.1));
+        assert!(approx(pf64(".0").unwrap(), 0.0));
+        assert!(approx(pf64(".1e-1").unwrap(), 0.01));
+        for bad in [".", ".e1", "0.e"] {
+            assert!(pf64(bad).is_err(), "{bad:?}");
+        }
+        assert!(approx(pf64("123142.1").unwrap(), 123_142.1));
+        assert!(approx(pf64("-123142.1124").unwrap(), -123_142.112_4));
+        assert!(approx(
+            pf64("2.71828182845904523536").unwrap(),
+            2.718_281_828_459_045
+        ));
+    }
+
+    #[test]
+    fn parse_float_nan_and_inf() {
+        assert!(pf64("nAn").unwrap().is_nan());
+        assert_eq!(pf64("inF"), Ok(f64::INFINITY));
+        assert_eq!(pf64("-INF"), Ok(f64::NEG_INFINITY));
+        assert_eq!(pf64("+Inf"), Ok(f64::INFINITY));
+        assert_eq!(pf32("-iNf"), Ok(f32::NEG_INFINITY));
+        assert_eq!(pf64("infinity"), Ok(f64::INFINITY));
+        assert_eq!(pf64("-InFiNiTy"), Ok(f64::NEG_INFINITY));
+        assert!(pf64("-nan").unwrap().is_nan());
+        for bad in ["infx", "infinit", "nanx", "in", "na", "infinityy", "i_nf"] {
+            assert!(pf64(bad).is_err(), "{bad:?}");
+        }
+    }
+
+    #[test]
+    fn format_float_d_matches_zig() {
+        assert_eq!(format_float_d(f64::NAN), "nan");
+        assert_eq!(format_float_d(-f32::NAN), "nan");
+        assert_eq!(format_float_d(f64::INFINITY), "inf");
+        assert_eq!(format_float_d(f64::NEG_INFINITY), "-inf");
+        assert_eq!(format_float_d(13.5f32), "13.5");
+        assert_eq!(format_float_d(-0.0f64), "-0");
+    }
+
+    #[test]
+    fn parse_float_largest_normals() {
+        assert_eq!(pf32("3.4028234664E38").unwrap().to_bits(), 0x7f7f_ffff);
+        assert_eq!(
+            pf64("1.7976931348623157E308").unwrap().to_bits(),
+            0x7fef_ffff_ffff_ffff
+        );
+    }
+
+    #[test]
+    fn parse_float_hex_special_and_zero() {
+        assert_eq!(pf32("0x9999p9999"), Ok(f32::INFINITY));
+        assert_eq!(pf32("-0x9999p9999"), Ok(f32::NEG_INFINITY));
+        assert_eq!(pf32("0x0"), Ok(0.0));
+        assert_eq!(pf32("-0x0"), Ok(0.0));
+        assert_eq!(pf32("0x0p42"), Ok(0.0));
+        assert_eq!(pf32("-0x0.00000p42"), Ok(0.0));
+        assert_eq!(pf32("0x0.00000p666"), Ok(0.0));
+    }
+
+    #[test]
+    fn parse_float_hex_f32() {
+        assert!(pf32("0x").is_err());
+        assert_eq!(pf32("0x1p0"), Ok(1.0));
+        assert_eq!(pf32("-0x1p-1"), Ok(-0.5));
+        assert_eq!(pf32("0x10p+10"), Ok(16384.0));
+        assert_eq!(pf32("0x10p-10"), Ok(0.015_625));
+        assert_eq!(pf32("0x0.ffffffp128"), Ok(hexf(0xff_ffff, 128 - 24)));
+        assert_eq!(pf32("0x1.fffffeP+127"), Ok(f32::MAX));
+        assert_eq!(pf32("-0x1.fffffeP+127"), Ok(-f32::MAX));
+        assert_eq!(pf32("0x1p-126"), Ok(f32::MIN_POSITIVE));
+        assert_eq!(pf32("-0x1p-126"), Ok(-f32::MIN_POSITIVE));
+        assert_eq!(pf32("0x1P-149"), Ok(f32::from_bits(1)));
+        assert_eq!(pf32("-0x1P-149"), Ok(-f32::from_bits(1)));
+    }
+
+    fn hexf(m: u32, e: i32) -> f32 {
+        m as f32 * 2f32.powi(e)
+    }
+
+    #[test]
+    fn parse_float_hex_f64() {
+        assert_eq!(pf64("0x1p0"), Ok(1.0));
+        assert_eq!(pf64("-0x1p-1"), Ok(-0.5));
+        assert_eq!(pf64("0x10p+10"), Ok(16384.0));
+        assert_eq!(pf64("0x10p-10"), Ok(0.015_625));
+        assert_eq!(pf64("0x1.fffffffffffffp+1023"), Ok(f64::MAX));
+        assert_eq!(pf64("-0x1.fffffffffffffp1023"), Ok(-f64::MAX));
+        assert_eq!(pf64("0x1p-1022"), Ok(f64::MIN_POSITIVE));
+        assert_eq!(pf64("-0x1p-1022"), Ok(-f64::MIN_POSITIVE));
+        assert_eq!(pf64("0x1p-1074"), Ok(f64::from_bits(1)));
+        assert_eq!(pf64("-0x1p-1074"), Ok(-f64::from_bits(1)));
+    }
+
+    #[test]
+    fn parse_float_hex_with_underscores_and_many_digits() {
+        assert_eq!(pf64("0x1.cp+3"), Ok(14.0));
+        assert_eq!(pf32("0x1.cp+3"), Ok(14.0));
+        assert_eq!(pf64("0X1_0"), Ok(16.0));
+        assert_eq!(pf64("0x1_0p1_0"), Ok(16.0 * 1024.0));
+        assert!(pf64("0x_1").is_err());
+        assert!(pf64("0x1_").is_err());
+        assert!(pf64("0x1p_1").is_err());
+        assert!(pf64("0x1__0").is_err());
+        // many_digits: result must match between f32 and a direct f32 round.
+        let a = pf32("0xffffffffffffffff.0p0").unwrap();
+        assert_eq!(a, 1.844_674_4e19_f32);
+        // Decimal numbers with underscores.
+        assert_eq!(pf32("1_4"), Ok(14.0));
+        assert!(pf32("1__4").is_err());
+    }
+}
diff --git a/crates/ghostty-renderer/src/generic.rs b/crates/ghostty-renderer/src/generic.rs
index 45357a2..97c410e 100644
--- a/crates/ghostty-renderer/src/generic.rs
+++ b/crates/ghostty-renderer/src/generic.rs
@@ -244,7 +244,7 @@ impl DerivedConfig {
             .value
             .iter()
             .filter_map(|p| {
-                let path = match p.path().to_path() {
+                let path = match p.path().to_syscall_path() {
                     Ok(path) => path,
                     Err(error) => {
                         log::warn!("invalid shader path: {error}");
@@ -869,7 +869,7 @@ impl<G: GraphicsApi> DrawState<G> {
         if let Some(p) = &self.config.bg_image
             && let Some(image) = p
                 .path()
-                .to_path()
+                .to_syscall_path()
                 .map_err(|error| log::warn!("invalid background image path: {error}"))
                 .ok()
                 .and_then(|path| load_background_image(&path))
diff --git a/crates/ghostty-termio/src/shell_integration.rs b/crates/ghostty-termio/src/shell_integration.rs
index 2b9ab7c..90b39c8 100644
--- a/crates/ghostty-termio/src/shell_integration.rs
+++ b/crates/ghostty-termio/src/shell_integration.rs
@@ -532,6 +532,17 @@ mod tests {
         assert_eq!(detect_shell(&sh("")), None);
     }
 
+    #[test]
+    fn detect_shell_splits_on_all_zig_separators() {
+        for sep in ["\n", "\r", "\t", " "] {
+            let v: Vec<_> = sh(&format!("bash{sep}-i")).arg_iterator().collect();
+            assert_eq!(v, ["bash", "-i"]);
+            assert_eq!(detect_shell(&sh(&format!("zsh{sep}-l"))), Some(Shell::Zsh));
+        }
+        // The first argument must end at the LF, not include `-i`.
+        assert_eq!(detect_shell(&sh("/bin/fish\n-l")), Some(Shell::Fish));
+    }
+
     #[test]
     fn arg_iterator_shell_and_direct() {
         let v: Vec<_> = sh("echo hello world").arg_iterator().collect();
diff --git a/docs/rewrite/notes/final-Z11.md b/docs/rewrite/notes/final-Z11.md
new file mode 100644
index 0000000..dda0ec9
--- /dev/null
+++ b/docs/rewrite/notes/final-Z11.md
@@ -0,0 +1,72 @@
+# Z11: RV9 gap groups (Ghostty 1.3.1 parity)
+
+Fixes for the six gap groups in `review-rv9-codex.md`. No version change, no commit.
+
+## Fixes
+
+1. **Interior NUL in font names.** `fontconfig::Pattern::add_string_bytes`
+   ends the value at the first NUL (the C-string handoff Zig does) instead of
+   failing, so `font-family`, `font-style` and codepoint-map families no longer
+   hit the `assert!` in `discovery::to_fc_pattern`.
+   Test: `discovery::tests::interior_nul_in_font_names_ends_the_c_string`.
+2. **Numeric grammars.** New `ghostty_os::zig_fmt`: exact ports of
+   `std.fmt.parseInt`/`parseUnsigned` (underscores, `0b/0o/0x` in both cases,
+   sign rules, `len > 2` prefix gate, Overflow vs InvalidCharacter) and
+   `std.fmt.parseFloat` (grammar of `parse.zig` incl. `validUnderscores`, hex
+   floats via a port of `convertHex` incl. the many-digits path, `inf`/
+   `infinity`/`nan`). Decimal values are rounded by Rust's correctly rounded
+   `FromStr` once the Zig grammar accepted the text. Ported all std tests.
+   Used by: primitive int/float fields (base 0), palette key (u8, base 0, Zig
+   error names), variation values, mouse-scroll bare float, quick-terminal
+   `px`/`%`, window-padding (u32, base 10), duration (`parseUnsigned` u64),
+   background-blur radius, codepoint/clipboard map hex (base 16), metric
+   modifiers, keybind numeric parameters (base 10 / float), ssh-cache entry
+   timestamp, `GIO_LAUNCHED_DESKTOP_FILE_PID`.
+   Also found by differential runs: Zig `{d}` prints `nan` (Rust `NaN`);
+   finalize clamps use Zig `@min/@max/clamp` NaN and +-0 semantics
+   (`cli_args::zig_min/zig_max/zig_clamp`); a failed `background-blur` radius
+   parse leaves `radius` (0 or the previous radius) like Zig's in-place union
+   initialisation.
+3. **C strings.** `config_capi` getters, C action titles/strings
+   (`action_c::Keep`) and the embedded clipboard write callback now end the C
+   string at the first NUL instead of deleting NUL bytes.
+4. **GTK new-window args.** `--working-directory=`/`--title=` trim only
+   `std.ascii.whitespace` (space, \t, \n, \r, VT, FF); U+00A0 etc. survive.
+5. **Shell tokenizer.** New `ghostty_os::arg_iterator::ArgIteratorGeneral`
+   (port of `std.process.ArgIteratorGeneral`, including `comments`/
+   `single_quotes` options, `skip`, NUL terminates). `Command::arg_iterator`
+   (and so shell-integration detection) use it: space, tab, CR and LF split.
+   Ported the std "response file arg parsing" test plus separator/quote/NUL
+   tests; termio test `detect_shell_splits_on_all_zig_separators`.
+6. **Parser diagnostics.** UTF-8 validation moved to where Zig would notice it:
+   metric modifiers (`InvalidFormat`), quick-terminal size (`MissingUnit`/
+   `InvalidValue`), `link` (`NotImplemented`), colors/palette
+   (`InvalidCharacter`), background-blur, keybind trigger (parsed after the
+   action, like `Parser.init`) and action parameters (known action with bad
+   bytes is `InvalidFormat`, unknown name `InvalidAction`).
+   Other differences found: config-file open errors are printed as
+   `error.FileNotFound` etc.; paths with interior NUL resolve/open as the C
+   string prefix (`EncodedOs::to_syscall_path`) for relative path expansion,
+   `config-file`, custom shaders, background image, gtk css.
+
+## Differential harness
+
+Script (not committed): for each of the 202 `Config.zig` fields x ~220 hostile
+and valid values, run `/usr/bin/ghostty +validate-config --config-file=F` and
+`+show-config` (value in `$XDG_CONFIG_HOME/ghostty/config`) against the Rust
+binary and compare exit code, stdout and stderr. Final state: zero mismatches
+except `theme` (resources path differs by install location),
+`auto-update-channel` default (`tip` vs `stable`, build channel) and
+`gtk-opengl-debug` (debug build).
+
+Regression tests: `crates/ghostty-config/tests/zig_parity.rs`,
+`ghostty_os::zig_fmt::tests`, `ghostty_os::arg_iterator::tests`,
+`ghostty-config` command tests, lib/gtk tests listed above.
+
+## Not covered / notes
+
+- `ghostty-terminal` OSC/tmux/kitty parsers also call `parseInt`
+  (`terminal/osc/parsers/*.zig`, `tmux/*.zig`, `kitty/*.zig`); they are outside
+  the config/input scope of this task and still use Rust `str::parse`/
+  `from_str_radix`. `zig_fmt` is available for a follow-up.
+- Windows/macOS behaviour is covered by cross-checks only.