fix(input): carry key and preedit text as bytes like Zig

Zig's KeyEvent.utf8 and the embedded API's key/preedit text are byte
slices passed through to key encoding and the pty; the port converted
them lossily to UTF-8.
- KeyEvent.utf8 is &[u8] end to end (ghostty-input encoder, core,
  ghostty-lib C API, libghostty-vt key events, GTK callers). Where Zig
  validates with Utf8View (alternates, modify-other-keys, ctrl CSI-u,
  associated text, binding unicode lookup) invalid text takes the same
  "no UTF-8" fallback.
- Invalid preedit UTF-8 behaves like Zig's `try Utf8View.init`: the
  prior preedit is cleared and marked dirty, the callback returns an
  error (logged by the C API) and no preedit is set.
- The inspector key widget shows invalid key text lossily, display only.

Test Plan:
- cargo test --workspace --no-fail-fast (3407 passed)
- cargo test -p ghostty-lib --features test-platform (C-API key text
  0xff 0xfe reaches the pty unchanged)
- just check-macos (both), just check-windows, just check-wasm

crates/ghostty-core/tests/common/mod.rs

@@ -486,7 +486,7 @@ impl Harness {
                 Mods::default()
             },
             composing: false,
-            utf8,
+            utf8: utf8.as_bytes(),
             unshifted_codepoint: unshifted,
         });
         // GTK reports the same text/codepoint on release.
@@ -496,7 +496,7 @@ impl Harness {
             mods,
             consumed_mods: Mods::default(),
             composing: false,
-            utf8,
+            utf8: utf8.as_bytes(),
             unshifted_codepoint: unshifted,
         });
         eff

crates/ghostty-core/tests/e2e_ime.rs

@@ -36,7 +36,7 @@ fn preedit_state_and_ime_point() {
     let h = harness!(Harness::recorder("", &[]));
     let before = h.surface.ime_point();
     h.surface
-        .preedit_callback(Some("\u{3042}\u{3044}"))
+        .preedit_callback(Some("\u{3042}\u{3044}".as_bytes()))
         .unwrap();
     {
         let st = h.surface.lock_state();
@@ -57,6 +57,20 @@ fn preedit_state_and_ime_point() {
     assert_eq!(h.recorded(), Vec::<u8>::new());
 }
 
+#[test]
+fn preedit_with_invalid_utf8_is_an_error_and_clears_prior() {
+    let h = harness!(Harness::recorder("", &[]));
+    // Like Zig's preeditCallback (`try Utf8View.init(text)`): invalid UTF-8
+    // returns an error after the prior preedit has been cleared, and no new
+    // preedit is set. Nothing is written to the pty.
+    h.surface.preedit_callback(Some(b"ab")).unwrap();
+    assert!(h.surface.lock_state().preedit.is_some());
+    assert!(h.surface.preedit_callback(Some(b"a\xffb\xc3")).is_err());
+    assert!(h.surface.lock_state().preedit.is_none());
+    h.settle(50);
+    assert_eq!(h.recorded(), Vec::<u8>::new());
+}
+
 #[test]
 fn preedit_is_rendered_and_cleared() {
     let h = harness!(Harness::recorder("", &[]));
@@ -71,7 +85,7 @@ fn preedit_is_rendered_and_cleared() {
         });
         b
     };
-    h.surface.preedit_callback(Some("abcd")).unwrap();
+    h.surface.preedit_callback(Some("abcd".as_bytes())).unwrap();
     h.wait("preedit visible", |h| {
         let r = region(h, cols.clone(), 0);
         !r.is_empty() && r != baseline
@@ -89,7 +103,7 @@ fn commit_sends_text_and_composing_keys_do_not() {
     h.key_event(KeyEvent {
         key: Key::KeyK,
         composing: true,
-        utf8: "k",
+        utf8: "k".as_bytes(),
         unshifted_codepoint: 'k' as u32,
         ..KeyEvent::default()
     });
@@ -98,12 +112,12 @@ fn commit_sends_text_and_composing_keys_do_not() {
 
     // Commit: preedit ends, committed text is sent with no key.
     h.surface
-        .preedit_callback(Some("\u{3053}\u{3093}"))
+        .preedit_callback(Some("\u{3053}\u{3093}".as_bytes()))
         .unwrap();
     h.surface.preedit_callback(None).unwrap();
     h.key_event(KeyEvent {
         key: Key::Unidentified,
-        utf8: "\u{3053}\u{3093}\u{306b}\u{3061}\u{306f}",
+        utf8: "\u{3053}\u{3093}\u{306b}\u{3061}\u{306f}".as_bytes(),
         ..KeyEvent::default()
     });
     h.expect_input("\u{3053}\u{3093}\u{306b}\u{3061}\u{306f}".as_bytes());
@@ -115,7 +129,7 @@ fn enter_with_committed_text_sends_text_not_cr() {
     let h = harness!(Harness::recorder("", &[]));
     h.key_event(KeyEvent {
         key: Key::Enter,
-        utf8: "\u{6f22}",
+        utf8: "\u{6f22}".as_bytes(),
         ..KeyEvent::default()
     });
     h.expect_input("\u{6f22}".as_bytes());

crates/ghostty-core/tests/e2e_keys.rs

@@ -250,7 +250,7 @@ fn key_release_without_press_is_ignored_in_legacy() {
     h.key_event(ghostty_input::KeyEvent {
         action: ghostty_input::key::Action::Release,
         key: Key::KeyA,
-        utf8: "a",
+        utf8: "a".as_bytes(),
         ..Default::default()
     });
     h.type_text("b");