feat(tmux-util): add go subcommand (attach-or-create)

tmux-util go <name> attaches to a session named <name> if it exists, creates it otherwise. Behavior depends on whether the caller is already inside tmux:

- Outside tmux: `tmux attach-session -t <name>` (existing) or `tmux new-session -s <name> -c $PWD` (new).
- Inside tmux (TMUX env set): `tmux switch-client -t <name>` (existing) or `tmux new-session -d -s <name> -c $PWD` followed by `switch-client` (new). Attaching from inside tmux would nest sessions and break the outer view, so the inside path uses switch-client instead.

The existence check uses `tmux has-session -t =<name>` with the leading `=` to force exact-match. Without it, tmux does prefix matching, which would let `go foo` resolve to a session named `foobar`.

I added 6 new tests covering both inside/outside-tmux paths, both create/attach paths, plus error handling for missing or empty name arguments. fake-tmux picked up handlers for new-session (mutates state), attach-session and switch-client (record-only), and the `=`-prefix form of has-session. Total suite: 32 tests, all green.

1 files changed, 35 insertions, 1 deletions

diff --git a/dotfiles/common/.local/bin/tmux-util b/dotfiles/common/.local/bin/tmux-util
index 2fa861d..4a7b596 100755
--- a/dotfiles/common/.local/bin/tmux-util
+++ b/dotfiles/common/.local/bin/tmux-util
@@ -36,6 +36,37 @@ EOF
 }
 
 # -----------------------------------------------------------------------------
+# go
+# -----------------------------------------------------------------------------
+
+cmd_go() {
+    local name="${1:-}"
+    if [ -z "$name" ]; then
+        echo "tmux-util go: missing session name" >&2
+        echo "Usage: tmux-util go <name>" >&2
+        return 2
+    fi
+
+    # `=name` forces exact match in `tmux has-session` (otherwise tmux does
+    # prefix matching, which would let `go foo` attach to a session named
+    # `foobar`).
+    if tmux has-session -t "=$name" 2>/dev/null; then
+        if [ -n "${TMUX:-}" ]; then
+            tmux switch-client -t "$name"
+        else
+            tmux attach-session -t "$name"
+        fi
+    else
+        if [ -n "${TMUX:-}" ]; then
+            tmux new-session -d -s "$name" -c "$PWD"
+            tmux switch-client -t "$name"
+        else
+            tmux new-session -s "$name" -c "$PWD"
+        fi
+    fi
+}
+
+# -----------------------------------------------------------------------------
 # ls
 # -----------------------------------------------------------------------------
 
@@ -144,7 +175,10 @@ main() {
         ls)
             cmd_ls "$@"
             ;;
-        go|pick|find|rename)
+        go)
+            cmd_go "$@"
+            ;;
+        pick|find|rename)
             echo "tmux-util: subcommand '$sub' is not implemented yet" >&2
             return 2
             ;;