"Smolder alone should leave no reason to use iTerm." — Dad
The Daily Driver You Do Not Own
A terminal you live in is not a text view. It is tabs, splits, a scrollback you search, a session you expect to still be there after lunch, and — in this family — a way for other apps to open a folder or a seat without pretending they are you. For years that daily driver was iTerm, with tmux sitting between the pane and the pixels whenever more than one job had to share a window.
That pairing looks complete from a distance. iTerm draws. tmux multiplexes. The shell runs. You can split, detach, reattach. The problem is not that any one of those programs is bad. The problem is the seam: two programs you do not own, talking through a serialized stream — of screens in ordinary use, of pane output and commands in tmux's control mode — with every family need sitting on the wrong side of it.
What a Seam Actually Costs
A pane, to a native app, is an object. You can move it, attach a process to it, ask what is in the foreground, copy a selection as text rather than as a rectangle of cells. A pane, to tmux, lives in tmux's own server and reaches the glass through tmux's own protocol. In ordinary use that protocol is a screen of cells, so selection becomes a parser. tmux's control mode is better: it hands iTerm2 pane IDs, per-pane output and a command channel, and iTerm2 draws tmux panes as its own native splits. But that only moves the parsing. The pane is still an object inside a program the family does not own, restore is still a question about what that server still holds, and a sibling that wants a folder in a new split has to speak tmux's command language through a third program, or pretend it is a human typing.
Every friction that sent a hand back to iTerm had this shape. Four harnesses in one window lagged, and the cause was unmeasured because the path from process to pixel crossed a multiplexer nobody here could instrument. A native file app wanted to open a folder in a terminal and had to go through Launch Services, which knows apps, not panes. A contest engine wanted four seats in one tab and got four independent windows, or a tmux layout that could not tell a judge from an author.
Name the Boundary
Smolder's answer is not "be iTerm, but ours." It is "own the pane boundary." One PTY stream per pane, an embedded emulator that turns that stream into pixels, native layout and selection, and a private attachment to a daemon that actually owns the process. No external multiplexer composes local panes. Remote tmux on a far host is a later, different sentence — it is not a license to wrap the local window in someone else's screen protocol.