feat(shell-integration): add integration for Elvish

- contains `.elv` file that implements the core of Elvish integration.
- does not contain routines needed for automatic integration.
- stored in `./elvish/lib/...` in preparation for automatic integration:
  Elvish imports `.../elvish/lib/*.elv`.

checklist:
- no confirmation on close where the cursor is at prompt:
  works, only occasionally doesn't, I'm not yet sure when.
- new terminals start in pwd of previously focused terminal: works
- prompts resize correctly: works
- triple-click while holding `ctrl` selects output of a command:
  works (when mouse is over the output)
- cursor at the prompt is turned into a bar: works
- ghostty:`jump_to_prompt` scrolls through prompts: works
- `opt`-click moves cursor at the prompt: works
- `sudo` preserves ghostty terminfo:
   untested - not sure when this is needed exactly, but did not encounter
   any errors after sudo, either

src/shell-integration/elvish/lib/ghostty-integration.elv

@@ -0,0 +1,87 @@
+{
+  fn set-prompt-state {|new| set-env __ghostty_prompt_state $new }
+
+  fn mark-prompt-start {
+    if (not-eq prompt-start (constantly $E:__ghostty_prompt_state)) {
+      printf "\e]133;D\a"
+    }
+    set-prompt-state 'prompt-start'
+    printf "\e]133;A\a"
+  }
+
+  fn mark-output-start {|_|
+    set-prompt-state 'pre-exec'
+    printf "\e]133;C\a"
+  }
+
+  fn mark-output-end {|cmd-info|
+    set-prompt-state 'post-exec'
+
+    var exit-status = 0
+
+    # in case of error: retrieve exit status,
+    # unless does not exist (= builtin function failure), then default to 1
+    if (not-eq $nil $cmd-info[error]) {
+      set exit-status = 1
+
+      if (has-key $cmd-info[error] reason) {
+        if (has-key $cmd-info[error][reason] exit-status) {
+          set exit-status = $cmd-info[error][reason][exit-status]
+        }
+      }
+    }
+
+    printf "\e]133;D;"$exit-status"\a"
+  }
+
+  fn report-pwd {
+    printf "\e]7;file://%s%s\a" (hostname) (pwd)
+  }
+
+  fn sudo-with-terminfo {|@args|
+    var sudoedit = $false
+    put $args | each {|arg|
+      use str
+      if (str:has-prefix $arg -) {
+        if (has-value [e -edit] $arg[1..]) {
+          set sudoedit = $true
+          break
+        }
+        continue
+      }
+
+      if (not (has-value $arg =)) { break }
+    }
+
+    if $sudoedit { set args = [ TERMINFO=$E:TERMINFO $@args ] }
+    command sudo $@args
+  }
+
+  set edit:before-readline = (conj $edit:before-readline $mark-prompt-start~)
+  set edit:after-readline  = (conj $edit:after-readline $mark-output-start~)
+  set edit:after-command   = (conj $edit:after-command $mark-output-end~)
+  set after-chdir = (conj $after-chdir {|_| report-pwd })
+
+  var no-cursor = (eq 1 $E:GHOSTTY_SHELL_INTEGRATION_NO_CURSOR)
+  var no-sudo   = (eq 1 $E:GHOSTTY_SHELL_INTEGRATION_NO_SUDO)
+
+  if $no-cursor {
+    fn beam  { printf "\e[5 q" }
+    fn block { printf "\e[0 q" }
+    set edit:before-readline = (conj $edit:before-readline $beam~)
+    set edit:after-readline  = (conj $edit:after-readline {|_| block })
+  }
+
+  try {
+    if (not $no-sudo) { return }
+    if (eq "" $E:TERMINFO) { return }
+    if (not-eq file (type -t sudo)) { return }
+
+    # overwrite root namespace `sudo`
+    edit:add-var sudo~ $sudo-with-terminfo~
+  } catch e { nop } # catch early returns, do nothing
+
+  mark-prompt-start
+  report-pwd
+}
+