docs: cli external editor (#6922)

documentation/docs/guides/environment-variables.md

@@ -157,6 +157,7 @@ These variables control how goose manages conversation sessions and context.
 | `GOOSE_MAX_TURNS` | [Maximum number of turns](/docs/guides/sessions/smart-context-management#maximum-turns) allowed without user input | Integer (e.g., 10, 50, 100) | 1000 |
 | `GOOSE_SUBAGENT_MAX_TURNS` | Sets the maximum turns allowed for a [subagent](/docs/guides/subagents) to complete before timeout | Integer (e.g., 25) | 25 |
 | `CONTEXT_FILE_NAMES` | Specifies custom filenames for [hint/context files](/docs/guides/context-engineering/using-goosehints#custom-context-files) | JSON array of strings (e.g., `["CLAUDE.md", ".goosehints"]`) | `[".goosehints"]` |
+| `GOOSE_PROMPT_EDITOR` | [External editor](/docs/guides/goose-cli-commands#external-editor-mode) to use for composing prompts instead of CLI input | Editor command (e.g., "vim", "code --wait") | Unset (uses CLI input) |
 | `GOOSE_CLI_THEME` | [Theme](/docs/guides/goose-cli-commands#themes) for CLI response  markdown | "light", "dark", "ansi" | "dark" |
 | `GOOSE_CLI_NEWLINE_KEY` | Customize the keyboard shortcut for [inserting newlines in CLI input](/docs/guides/goose-cli-commands#keyboard-shortcuts) | Single character (e.g., "n", "m") | "j" (Ctrl+J) |
 | `GOOSE_RANDOM_THINKING_MESSAGES` | Controls whether to show amusing random messages during processing | "true", "false" | "true" |
@@ -187,6 +188,9 @@ export GOOSE_SUBAGENT_MAX_TURNS=50
 # Use multiple context files
 export CONTEXT_FILE_NAMES='["CLAUDE.md", ".goosehints", ".cursorrules", "project_rules.txt"]'
 
+# Use vim for composing prompts
+export GOOSE_PROMPT_EDITOR=vim
+
 # Set the ANSI theme for the session
 export GOOSE_CLI_THEME=ansi