A session whose tmux client the probe could not map no longer proves that the agent left. It is a gap for that pane only: the tracker keeps the bound agent, counts no miss, and binds nothing new. The new correlation tmuxUnreachable tells the user why: the pane badge shows a warning that names tmux -S, and --json reports remote.correlation tmux_unreachable. A degraded OSC-only binding is not allowed there, because tmux drops OSC 7501. The docs describe the screen budget, the kept bottom lines, and the tmux limits.