shell-init: record the first command of every shell in atuin

bash-preexec arms its DEBUG trap from __bp_interactive_mode at the end of
PROMPT_COMMAND, but its lazy installer runs mid-way through the first prompt
because zoxide and ghostty append their hooks after it. Those hooks disarm the
trap again, so the first interactive command of every session never reached
preexec and atuin silently dropped it.

Arm from PS0 instead, which is expanded once per interactive command before the
DEBUG trap and is therefore independent of PROMPT_COMMAND ordering.

Also guard the script against running twice: it is installed as both
loginShellInit and interactiveShellInit, and /etc/profile sources /etc/bashrc,
which registered starship's precmd/preexec hooks twice in every login shell.

scripts/shell-init.sh

@@ -37,18 +37,43 @@ fi
 
 (( INTERACTIVE )) || return 0
 
+# ---- run-once guard --------------------------------------------------------
+
+# Installed as both loginShellInit (/etc/profile) and interactiveShellInit
+# (/etc/bashrc), and /etc/profile sources /etc/bashrc, so a login shell would run
+# this twice and register starship's hooks twice. Not exported: child shells must
+# initialise on their own.
+if [[ -n ${NANUQSAURUS_SHELL_INIT_DONE:-} ]]; then
+  log_shell_init "already initialised, skipping"
+  return 0
+fi
+NANUQSAURUS_SHELL_INIT_DONE=1
+
 # ---- bash-preexec ----------------------------------------------------------
 
 if [[ -n ${BASH_VERSION:-} && -z ${bash_preexec_imported:-} && -r "@BASHPREEXEC@" ]]; then
   # shellcheck disable=SC1090
   . "@BASHPREEXEC@"
-  # Do NOT call __bp_install here. bash-preexec must install on the FIRST prompt,
-  # after starship/atuin/zoxide/ghostty have modified PROMPT_COMMAND, so that
-  # __bp_interactive_mode stays the LAST PROMPT_COMMAND entry. Installing eagerly
-  # lets later hooks land after it and silently breaks preexec (atuin recording).
   log_shell_init "bash-preexec loaded"
 fi
 
+# bash-preexec arms its DEBUG trap from __bp_interactive_mode, which it appends to
+# the END of PROMPT_COMMAND -- but its lazy installer runs in the MIDDLE of the
+# first prompt, because zoxide (below) and ghostty (~/.bashrc) append their hooks
+# after it. Those hooks then disarm the trap again, so the first command of every
+# session never reaches preexec and atuin never records it. PS0 is expanded once
+# per interactive command, before the DEBUG trap, so arming there is independent of
+# PROMPT_COMMAND ordering. Needs the non-forking ${ ...; } funsub (bash >= 5.3);
+# older bash keeps the previous behaviour.
+if [[ -n ${bash_preexec_imported:-} ]] &&
+   ((BASH_VERSINFO[0] > 5 || (BASH_VERSINFO[0] == 5 && BASH_VERSINFO[1] >= 3))); then
+  # shellcheck disable=SC2016
+  __nanuq_bp_arm='${ __bp_preexec_interactive_mode=on; }'
+  [[ ${PS0-} == *"$__nanuq_bp_arm"* ]] || PS0=$__nanuq_bp_arm${PS0-}
+  unset __nanuq_bp_arm
+  log_shell_init "bash-preexec PS0 arming enabled"
+fi
+
 # ---- starship --------------------------------------------------------------
 
 if have @STARSHIP@; then
@@ -57,8 +82,7 @@ if have @STARSHIP@; then
     */bash) eval "$(@STARSHIP@ init bash)" ;;
     */zsh)  eval "$(@STARSHIP@ init zsh)" ;;
   esac
-  # starship's bash init registers starship_precmd/starship_preexec_all with
+  # registers starship_precmd/starship_preexec_all with bash-preexec directly
-  # bash-preexec directly; no manual PROMPT_COMMAND wiring needed.
 else
   log_shell_init "starship skipped"
 fi
@@ -77,8 +101,7 @@ if have @ATUIN@; then
     */bash) eval "$(@ATUIN@ init bash)" ;;
     */zsh)  eval "$(@ATUIN@ init zsh)" ;;
   esac
-  # atuin's init registers __atuin_preexec/__atuin_precmd with bash-preexec
+  # registers __atuin_preexec/__atuin_precmd with bash-preexec itself
-  # itself; manual array wiring only caused duplicate hook entries.
 else
   log_shell_init "atuin skipped"
 fi
@@ -91,9 +114,7 @@ if have zoxide; then
     */bash) eval "$(zoxide init bash)" ;;
     */zsh)  eval "$(zoxide init zsh)" ;;
   esac
-  # zoxide's bash init hooks into bash-preexec (precmd_functions) when it is
+  # appends __zoxide_hook to PROMPT_COMMAND; see the PS0 note above
-  # present; manual PROMPT_COMMAND wiring only pushed hooks past
-  # __bp_interactive_mode and broke preexec ordering.
 else
   log_shell_init "zoxide skipped"
 fi