Automatic prefix change to C-a when in ssh or mosh session

.config/tmux-prefix-detect.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+# Auto-set tmux prefix based on connection type.
+# Called from tmux hooks: session-created and client-attached.
+if tmux show-environment SSH_CONNECTION 2>/dev/null | grep -qv '^-' || \
+   tmux show-environment MOSH_SERVER_PID 2>/dev/null | grep -qv '^-'; then
+    tmux set -g prefix C-a
+    tmux bind-key C-a send-prefix
+    tmux unbind-key C-b 2>/dev/null
+    tmux display-message "Prefix: C-a (remote)"
+else
+    tmux set -g prefix C-b
+    tmux bind-key C-b send-prefix
+    tmux unbind-key C-a 2>/dev/null
+    tmux display-message "Prefix: C-b (local)"
+fi

.tmux.conf

@@ -18,5 +18,13 @@ set -g @plugin 'tmux-plugins/tmux-sensible'
 # set -g @plugin 'git@github.com:user/plugin'
 # set -g @plugin 'git@bitbucket.com:user/plugin'
 set-window-option -g mode-keys vi
+
+# Auto-switch prefix: C-a for SSH/mosh, C-b for local
+set -ga update-environment 'MOSH_SERVER_PID'
+set-hook -g session-created  'run-shell ~/.config/tmux-prefix-detect.sh'
+set-hook -g client-attached  'run-shell ~/.config/tmux-prefix-detect.sh'
+
+# Manual override: prefix+T to toggle
+bind T run-shell ~/.config/tmux-prefix-detect.sh
 # Initialize TMUX plugin manager (keep this line at the very bottom of tmux.conf)
 run '~/.tmux/plugins/tpm/tpm'