Tauri GUI bundle's minimal PATH made tmux silently exit

Symptom

After switching from a bare shell to a tmux-backed shell per pane, every newly opened pane immediately rendered [exited], and panes opened afterwards looked like they were sharing output with the first one.

Cause

Two coupled problems.

1. Tauri's GUI process inherits a minimal PATH — typically /usr/bin:/bin:/usr/sbin:/sbin, not the user's interactive-shell PATH. Homebrew binaries (/opt/homebrew/bin/tmux) were not on it.
2. CommandBuilder::new("tmux") failed silently. The spawn errored out before any output reached the renderer, the PTY simply closed, and xterm rendered the close as [exited]. With no visible error to read, it looked like the panes were sharing one session.

Fix

Three changes in apps/desktop/src-tauri/src/pty.rs:

// 1. Resolve tmux against known absolute paths before trusting PATH.
fn find_tmux() -> String {
    let candidates = [
        "/opt/homebrew/bin/tmux", "/usr/local/bin/tmux",
        "/usr/bin/tmux",          "/opt/local/bin/tmux",
    ];
    for path in &candidates {
        if Path::new(path).exists() { return path.to_string(); }
    }
    "tmux".to_string()
}
 
// 2. Augment PATH for the child process.
fn augmented_path() -> String {
    let extra = "/opt/homebrew/bin:/usr/local/bin";
    match std::env::var("PATH") {
        Ok(p) if p.contains("/opt/homebrew/bin") || p.contains("/usr/local/bin") => p,
        Ok(p) => format!("{}:{}", extra, p),
        Err(_) => format!("{}:/usr/bin:/bin", extra),
    }
}
 
// 3. Wrap the tmux invocation in bash so a failure surfaces *visibly*.
let cmd_str = format!(
    "{tmux} new-session -A -D -s {sess} 2>&1; \
     status=$?; \
     if [ $status -ne 0 ]; then \
       echo ''; \
       echo '⚠️  tmux exited with code '$status'. tmux_path='{tmux}; \
       echo 'Falling back to interactive shell. Try: tmux ls'; \
     fi; \
     exec ${{SHELL:-/bin/bash}}",
    tmux = tmux_path, sess = tmux_session,
);

Commit: 4ad76e7. Codified as CLAUDE.md RULE #5c ("wrap fallible binaries with a visible error path") and RULE #5d ("PTY EOF must be visible").

Pattern

Two compounding rules for any subprocess in a GUI app:

• The GUI app's PATH is not your shell's PATH. Augment it explicitly, and resolve known-location binaries by absolute path.
• A silent spawn failure looks like a hung pane. Always wrap fallible binaries so their failure prints something the user can read.

A frozen pane with no output is the worst possible UX — the user can't tell whether the process died, is hung, or is just slow.