linux: wire keyboard, mouse, and focus input to libghostty

[Jesssullivan]

Summary

• Add GTK4 event controllers for all input types to the terminal surface
• Keyboard: GtkEventControllerKey → ghostty_surface_key with GDK keyval→text conversion and modifier translation
• Mouse buttons: GtkGestureClick (all buttons) → ghostty_surface_mouse_button with position tracking
• Mouse motion: GtkEventControllerMotion → ghostty_surface_mouse_pos
• Scroll: GtkEventControllerScroll (both axes + discrete) → ghostty_surface_mouse_scroll
• Focus: GtkEventControllerFocus enter/leave → ghostty_surface_set_focus
• Shared helpers: gtkModsToGhostty (modifier translation), gtkButtonToGhostty (button number mapping)

This is the critical missing piece that makes the terminal interactive — keyboard input and mouse events now reach the terminal process. Combined with PR #237 (close/title/pwd) and PR #238 (actions/clipboard), the Linux port now has a functional input→render→clipboard pipeline.

Test plan

• CI compilation passes across all Linux distros
• On honey: launch cmux, verify typing produces output in terminal
• On honey: verify mouse selection works (click + drag)
• On honey: verify scroll works in less or man
• On honey: verify Ctrl+C interrupts a running process

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR wires all GTK4 input (keyboard, mouse, scroll, focus) to libghostty via event controllers, and adds action handlers for close/quit/maximize/child-exit/config in the Linux port. Signal handler signatures, modifier translation, and button mapping are all correct.

Two P2 items worth tracking before the Linux port stabilises:

• unshifted_codepoint is derived from gdk_keyval_to_lower, which returns incorrect values for shifted symbol keys (e.g. Shift+1 → ! instead of 1), breaking the kitty keyboard protocol for those keys.
• The heap-allocated Surface struct is never freed when a terminal panel closes (g_object_set_data has no GDestroyNotify, and onCloseSurface does not call alloc.destroy).

Confidence Score: 4/5

Safe to merge for the MVP milestone; two P2 issues should be tracked before the Linux port reaches broad use.

All new signal wiring is structurally correct and the action handlers are sound. Two P2 findings exist: a correctness gap in keyboard protocol data (unshifted_codepoint) and a per-close memory leak that accumulates over a multiplexer session. Neither blocks basic operation but both affect reliability over time.

cmux-linux/src/surface.zig — unshifted_codepoint computation and missing Surface deallocation on close.

Important Files Changed

Filename	Overview
cmux-linux/src/surface.zig	Adds GTK4 event controllers for keyboard, mouse, scroll, and focus; unshifted_codepoint is computed with gdk_keyval_to_lower which is incorrect for shifted symbol keys, and the heap-allocated Surface struct is never freed on close.
cmux-linux/src/app.zig	Adds close, quit, maximize, child-exit, reload-config, color-change, renderer-health, and set-tab-title action handlers; logic is correct but onCloseSurface does not free the Surface wrapper allocated in surface.zig.
cmux-linux/src/main.zig	Wires close_surface_cb into the ghostty runtime config; straightforward and correct.

Sequence Diagram

sequenceDiagram
    participant GTK as GTK4 Event Controllers
    participant Surface as surface.zig (Surface)
    participant Ghostty as libghostty

    GTK->>Surface: key-pressed (keyval, keycode, state)
    Surface->>Surface: gtkModsToGhostty(state)
    Surface->>Surface: gdk_keyval_to_unicode(keyval) → text
    Surface->>Ghostty: ghostty_surface_key(key_event)

    GTK->>Surface: GtkGestureClick pressed (n_press, x, y)
    Surface->>Surface: gtk_widget_grab_focus()
    Surface->>Surface: gtkButtonToGhostty(button)
    Surface->>Ghostty: ghostty_surface_mouse_pos(x, y, mods)
    Surface->>Ghostty: ghostty_surface_mouse_button(PRESS, button, mods)

    GTK->>Surface: motion (x, y)
    Surface->>Ghostty: ghostty_surface_mouse_pos(x, y, mods)

    GTK->>Surface: scroll (dx, dy)
    Surface->>Ghostty: ghostty_surface_mouse_scroll(dx, dy, scroll_mods)

    GTK->>Surface: focus enter
    Surface->>Ghostty: ghostty_surface_set_focus(true)

    Ghostty->>Surface: close_surface_cb(userdata)
    Surface->>Surface: ws.removePanel() [Surface struct not freed ⚠]

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[greptile-apps]

consumed_mods always zero may cause double-modifier effects

Hardcoding consumed_mods = GHOSTTY_MODS_NONE means ghostty never learns that a modifier was "consumed" producing the text character. For Shift+letter ghostty would see both the shift modifier and the uppercase letter, and may emit an extra modifier keypress sequence. Ideally, when text_len > 0 and the keyval differs from its lowercase version, GHOSTTY_MODS_SHIFT should be included in consumed_mods. This matches the approach in ghostty/src/apprt/gtk/Surface.zig where consumed mods are derived from the GTK key event's consumed_modifiers.

[Jesssullivan]

Ditto, I think we should take note of this