Fixes for the OSC prompt script (#39588)

profile.d/80-systemd-osc-context.sh

@@ -13,6 +13,10 @@
 # Not bash?
 [ -n "${BASH_VERSION:-}" ] || return 0
 
+# If we're on a "dumb" terminal, do not install the prompt.
+# Treat missing $TERM same as "dumb".
+[ "${TERM:-dumb}" = "dumb" ] && return 0
+
 __systemd_osc_context_escape() {
     # Escape according to the OSC 3008 spec. Since this requires shelling out
     # to 'sed' we'll only do it where it's strictly necessary, and skip it when
@@ -56,8 +60,12 @@ __systemd_osc_context_precmdline() {
     read -r systemd_osc_context_cmd_id </proc/sys/kernel/random/uuid
 }
 
-if [[ -n "${BASH_VERSION:-}" ]] && [[ "${TERM:-}" != "dumb" ]]; then
-    # Whenever a new prompt is shown close the previous command, and prepare new command
+if [ -n "${BASH_VERSION:-}" ]; then
+    # Legacy bashrc will assign PROMPT_COMMAND=, which is equivalent to assigning
+    # index 0 in the array. Leave an empty spot to handle this gracefully.
+    [ -n "$(declare -p PROMPT_COMMAND 2>/dev/null)" ] || PROMPT_COMMAND+=('')
+
+    # Whenever a new prompt is shown, close the previous command, and prepare new command
     PROMPT_COMMAND+=(__systemd_osc_context_precmdline)
 
     # PS0 is shown right after a prompt completed, but before the command is executed