Shell integration: bash: Fix rendering of multiline prompts with more than two lines

Fixes #4681

docs/changelog.rst

@@ -115,6 +115,8 @@ Detailed list of changes
 
 - Shell integration: bash: Dont fail if an existing PROMPT_COMMAND ends with a semi-colon (:iss:`4645`)
 
+- Shell integration: bash: Fix rendering of multiline prompts with more than two lines (:iss:`4681`)
+
 - Linux: Fix fontconfig alias not being used if the aliased font is dual spaced instead of monospaced (:iss:`4649`)
 
 - macOS: Add an option :opt:`macos_menubar_title_max_length` to control the max length of the window title displayed in the global menubar (:iss:`2132`)

shell-integration/bash/kitty.bash

@@ -54,9 +54,13 @@ _ksi_main() {
             PS1="${_ksi_prompt[ps1]}$PS1"
             if [[ "${_ksi_prompt[mark]}" == "y" ]]; then 
                 # bash does not redraw the leading lines in a multiline prompt so
-                # mark them as secondary prompts
+                # mark the last line as a secondary prompt. Otherwise on resize the
+                # lines before the last line will be erased by kitty.
                 PS1=${PS1//\\\[\\e\]133;k;start_secondary_kitty\\a\\\]*end_secondary_kitty\\a\\\]}
-                PS1=${PS1//"\n"/${_ksi_prompt[secondary_prompt]}}
+                # the first part removes everything from the last \n onwards
+                # the second part appends a newline with the secondary marking 
+                # the third part appends everything after the last newline
+                PS1=${PS1%'\n'*}${_ksi_prompt[secondary_prompt]}${PS1##*'\n'}
             fi
         fi
         if [[ -n "${_ksi_prompt[ps1_suffix]}" ]]; then