tmux: terminal's replies to startup capability probes printed at the prompt #40035

hi!

i found a bug where launching opencode inside tmux prints the terminal's replies to
opencode's own startup capability probes as literal text at the prompt.

the replies start with ESC [, and tmux parses that as M-[ before the rest reaches
the pane. i have M-[ bound, so each reply also flips me to another window:

bind -n M-[ previous-window          # Opt+[
bind -n M-] next-window              # Opt+]

what lands in the terminal:

?2027;1$y?2026;2$y

the ESC [ is missing from the visible text because tmux consumed it as the binding.
that's probably also the tab-switching reported in #22210 and #15744.

i think this bug is the same one that was reported in #22210, #16547 and #15744,
which were all auto-closed, and it still reproduces on 1.18.5.

Plugins: none

OpenCode version: 1.18.5

Steps to reproduce:

1. tmux with set -g allow-passthrough on
2. open two or more windows
3. run opencode in one of them
4. escape sequence text appears at the prompt

Operating System: macOS 26.5.2 (arm64)

Terminal: ghostty 1.3.1 + tmux 3.7b, TERM=tmux-256color