preexec: set options before load

By setting `__bp_delay_install`, we avoid any immediate initialization at all. We then override two troublesome functions before calling `__bp_install_after_session_init()`.

The `__bp_install_after_session_init()` function doesn't enable the DEBUG trap, just sets `$PROMPT_COMMAND` to include `__bp_install()`, so the actual final `$PROMPT_COMMAND` is not finished, and DEBUG trap set, until after the first prompt is displayed.

bash_it.sh

@@ -155,6 +155,3 @@ if ! _command_exists reload && [[ -n "${BASH_IT_RELOAD_LEGACY:-}" ]]; then
 			;;
 	esac
 fi
-
-# Disable trap DEBUG on subshells - https://github.com/Bash-it/bash-it/pull/1040
-set +T

vendor/init.d/preexec.bash

@@ -1,3 +1,25 @@
 # shellcheck shell=bash
-# shellcheck disable=1090
-source "${BASH_IT}"/vendor/github.com/rcaloras/bash-preexec/bash-preexec.sh
+# shellcheck disable=SC2034
+#
+# Load the `bash-preexec.sh` library, and define helper functions
+
+## Prepare, load, fix, and install `bash-preexec.sh`
+
+# Disable immediate `$PROMPT_COMMAND` modification
+__bp_delay_install="delayed"
+
+# shellcheck source-path=SCRIPTDIR/../github.com/rcaloras/bash-preexec
+source "${BASH_IT?}/vendor/github.com/rcaloras/bash-preexec/bash-preexec.sh"
+
+# Block damanaging user's `$HISTCONTROL`
+function __bp_adjust_histcontrol() { :; }
+
+# Don't fail on readonly variables
+function __bp_require_not_readonly() { :; }
+
+# Disable trap DEBUG on subshells - https://github.com/Bash-it/bash-it/pull/1040
+__bp_enable_subshells= # blank
+set +T
+
+# Modify `$PROMPT_COMMAND` now
+__bp_install_after_session_init