fix: close remaining gaps found by the completeness audit

Addresses the partial ports listed in
docs/rewrite/notes/review-completeness-codex.md (details in
docs/rewrite/notes/gaps-X2.md):
- Flatpak: the exit watcher no longer consumes the host command; a
  shared FlatpakSignalHandle lets closing a surface still SIGHUP the
  host process group.
- Child environment is byte-preserving end to end (ghostty_os::EnvMap
  of OsStrings) and Snap paths are filtered like filterSnapPaths.
- argv handling no longer panics on non-UTF-8 arguments.
- URI percent-decoding keeps raw bytes; OSC 7 pwd is passed through
  without lossy conversion.
- Keybinding comparison/hashing uses full Unicode case folding from a
  table generated from CaseFolding.txt (Unicode 17.0.0).
- Link regexes set Oniguruma's whole-search retry limit through the new
  minimal ghostty-onig crate (one SAFETY-commented FFI call).
- OSC 9 NUL-capacity check ordering matches Zig.
- Wayland registry binds/clears globals advertised after startup.
- Custom shaders may pass sampler2D to helper functions (naga adapter).
- +list-themes preview renders OSC 8 links, styled underlines and
  follows color-scheme reports.

Also includes the inspector's integration edits in shared files
(renderer state hook, termio VT recording, core/apprt-gtk wiring), X1's
config/input/cli additions for completion generation, and a fix for a
race in the termio backpressure test (it wrote before `stty raw`
applied, so the cooked line discipline dropped bytes past MAX_CANON).

Test Plan:
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings

crates/ghostty-unicode/src/case_folding.rs

@@ -0,0 +1,63 @@
+//! Full Unicode case folding (`CaseFolding.txt` statuses `C` + `F`, Unicode
+//! 17.0.0), equivalent to uucode's `case_folding_full` field.
+//!
+//! The table is generated by `build.rs` from `ucd/CaseFolding.txt`.
+
+include!(concat!(env!("OUT_DIR"), "/case_folding_full.rs"));
+
+/// The full case folding of `cp`, or `None` if it folds to itself.
+///
+/// The result has 1 to 3 codepoints (unused trailing entries are `0`); use
+/// [`fold_full`] for a slice.
+#[must_use]
+pub fn lookup(cp: u32) -> Option<[u32; 3]> {
+    CASE_FOLDING_FULL
+        .binary_search_by_key(&cp, |e| e.0)
+        .ok()
+        .map(|i| CASE_FOLDING_FULL[i].1)
+}
+
+/// The full case folding of `cp` as a zero-padded 3-element array. Like
+/// uucode's `.with(&buffer, cp)`, a codepoint without a folding folds to
+/// itself.
+#[must_use]
+pub fn fold_full(cp: u32) -> [u32; 3] {
+    lookup(cp).unwrap_or([cp, 0, 0])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn simple_and_identity() {
+        assert_eq!(fold_full('A' as u32), ['a' as u32, 0, 0]);
+        assert_eq!(fold_full('a' as u32), ['a' as u32, 0, 0]);
+        assert_eq!(fold_full('1' as u32), ['1' as u32, 0, 0]);
+        assert_eq!(fold_full(0x00B5), [0x03BC, 0, 0]);
+        assert_eq!(fold_full(0x017F), ['s' as u32, 0, 0]);
+        assert_eq!(fold_full(0x03C2), [0x03C3, 0, 0]);
+        assert_eq!(fold_full(0x1E9E), [0x73, 0x73, 0]);
+    }
+
+    #[test]
+    fn multi_codepoint() {
+        // U+00DF LATIN SMALL LETTER SHARP S -> "ss"
+        assert_eq!(fold_full(0x00DF), [0x73, 0x73, 0]);
+        // U+0390 -> 03B9 0308 0301
+        assert_eq!(fold_full(0x0390), [0x03B9, 0x0308, 0x0301]);
+        // U+FB03 LATIN SMALL LIGATURE FFI -> "ffi"
+        assert_eq!(fold_full(0xFB03), [0x66, 0x66, 0x69]);
+    }
+
+    #[test]
+    fn table_sorted_and_nonempty() {
+        assert!(CASE_FOLDING_FULL.len() > 1500);
+        assert!(CASE_FOLDING_FULL.windows(2).all(|w| w[0].0 < w[1].0));
+    }
+
+    #[test]
+    fn dotted_capital_i_uses_full_folding() {
+        assert_eq!(fold_full(0x0130), [0x69, 0x307, 0]); // F entry for dotted I
+    }
+}

crates/ghostty-unicode/src/lib.rs

@@ -8,6 +8,7 @@
 
 #![cfg_attr(test, allow(clippy::unwrap_used))]
 
+pub mod case_folding;
 pub mod emoji_table;
 pub mod grapheme;
 pub mod lut;