linux: implement runtime callbacks (close surface, set title, pwd)

[Jesssullivan]

Summary

• Set surface_config.userdata to the GtkWidget pointer during surface creation
• Implement onCloseSurface callback: walks tab manager to find the owning panel, removes it, closes empty workspaces
• Fixes dead shells remaining visible after terminal process exit

Previously onCloseSurface was a no-op stub (identified as a remaining gap from #207). Now libghostty's close notification properly triggers panel cleanup.

Design notes

• Iterator safety: captures panel ID before calling removePanel to avoid hash map iterator invalidation
• No double-free: panel.surface is always null (ghostty surface lives on the Surface wrapper, not the panel struct), so removePanel's ghostty_surface_free guard is a no-op — the surface is already freed by libghostty before calling the callback
• Last-workspace guard: won't close the final workspace, preserving a usable window state

Test plan

• Code review: no iterator invalidation, no double-free
• Launch cmux-linux, open terminal, run exit — panel should be removed
• With multiple workspaces: exit last shell in a workspace → workspace closes
• Single workspace with single shell: exit → workspace stays (empty but present)

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR implements onCloseSurface to clean up terminal panels on process exit, and also adds handleSetTitle/handlePwd action handlers for shell title and directory integration. The close-surface logic is well-structured (iterator-safe, no double-free), but the two new action handlers leak memory on every update.

• handleSetTitle (line 39): overwrites panel.title without freeing the old allocation — leaks on every shell prompt that sets a title.
• handlePwd (lines 67–68): same issue for panel.directory and ws.current_directory — leaks on every PWD update from shell integration.

Confidence Score: 4/5

Safe to merge after fixing two memory leaks in the new action handlers; the core close-surface logic is correct.

Two P1 memory leaks are introduced by the new handleSetTitle and handlePwd functions — they accumulate unboundedly during normal terminal use (every shell prompt or directory change). The onCloseSurface implementation itself is correct. Score is 4 pending the leak fixes.

cmux-linux/src/app.zig — handleSetTitle (line 39) and handlePwd (lines 67–68)

Important Files Changed

Filename	Overview
cmux-linux/src/app.zig	Implements onCloseSurface (panel cleanup on terminal exit), handleSetTitle, and handlePwd. The close-surface logic is correct (iterator-safe, no double-free), but handleSetTitle and handlePwd leak the previous panel.title, panel.directory, and ws.current_directory allocations on every update.
cmux-linux/src/surface.zig	Adds surface_config.userdata = gl_area during onRealize so onCloseSurface can match the callback to the owning panel. Change is minimal and correct.

Sequence Diagram

sequenceDiagram
    participant GH as libghostty
    participant CB as app.zig callbacks
    participant WS as Workspace
    participant TM as TabManager

    GH->>CB: onCloseSurface(userdata=GtkWidget*)
    CB->>TM: getTabManager()
    CB->>WS: iterate panels to find widget
    CB->>WS: removePanel(panel_id)
    alt workspace empty && not last
        CB->>TM: closeWorkspace(ws_idx)
        TM->>WS: deinit + destroy
        TM-->>TM: remove AdwTabView page
    end

    GH->>CB: onAction(SET_TITLE)
    CB->>CB: getSurfaceUserdata(target)
    CB->>WS: iterate panels to find widget
    CB->>WS: panel.title = dupe(title_str)
    Note over CB,WS: old panel.title not freed
    CB->>WS: ws.setTitle(title_str)
    CB->>TM: updateTabTitle(ws)

    GH->>CB: onAction(PWD)
    CB->>CB: getSurfaceUserdata(target)
    CB->>WS: iterate panels to find widget
    CB->>WS: panel.directory = dupe(pwd_str)
    Note over CB,WS: old panel.directory not freed
    CB->>WS: ws.current_directory = dupe(pwd_str)
    Note over CB,WS: old ws.current_directory not freed

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_{Reviews (1): Last reviewed commit: "linux: handle SET_TITLE and PWD actions ..." | Re-trigger Greptile}

[greptile-apps]

Memory leak: old panel.title not freed before replacement

panel.title is overwritten on every set_title escape sequence (which fires on each shell prompt change) without freeing the previous allocation. Over a long session this grows unboundedly. Compare with ws.setTitle() which correctly frees first.

Suggested change

	panel.title = ws.alloc.dupe(u8, title_str) catch null;
	if (panel.title) |old| ws.alloc.free(old);
	panel.title = ws.alloc.dupe(u8, title_str) catch null;

[greptile-apps]

Memory leak: old panel.directory / ws.current_directory not freed

Both slices are overwritten without freeing the previous allocation, leaking memory on every shell PWD integration update. Same fix pattern as ws.setTitle():

Suggested change

	panel.directory = ws.alloc.dupe(u8, pwd_str) catch null;
	ws.current_directory = ws.alloc.dupe(u8, pwd_str) catch null;
	if (panel.directory) |old| ws.alloc.free(old);
	panel.directory = ws.alloc.dupe(u8, pwd_str) catch null;
	if (ws.current_directory) |old| ws.alloc.free(old);
	ws.current_directory = ws.alloc.dupe(u8, pwd_str) catch null;