feat(coding-agent): add external editor setting

Closes #6122

packages/coding-agent/src/modes/interactive/components/extension-editor.ts

@@ -28,6 +28,7 @@ export class ExtensionEditorComponent extends Container implements Focusable {
 	private onCancelCallback: () => void;
 	private tui: TUI;
 	private keybindings: KeybindingsManager;
+	private externalEditorCommand: string | undefined;
 
 	private _focused = false;
 	get focused(): boolean {
@@ -46,11 +47,13 @@ export class ExtensionEditorComponent extends Container implements Focusable {
 		onSubmit: (value: string) => void,
 		onCancel: () => void,
 		options?: EditorOptions,
+		externalEditorCommand?: string,
 	) {
 		super();
 
 		this.tui = tui;
 		this.keybindings = keybindings;
+		this.externalEditorCommand = externalEditorCommand;
 		this.onSubmitCallback = onSubmit;
 		this.onCancelCallback = onCancel;
 
@@ -76,7 +79,7 @@ export class ExtensionEditorComponent extends Container implements Focusable {
 		this.addChild(new Spacer(1));
 
 		// Add hint
-		const hasExternalEditor = !!(process.env.VISUAL || process.env.EDITOR);
+		const hasExternalEditor = !!this.getExternalEditorCommand();
 		const hint =
 			keyHint("tui.select.confirm", "submit") +
 			"  " +
@@ -110,8 +113,16 @@ export class ExtensionEditorComponent extends Container implements Focusable {
 		this.editor.handleInput(keyData);
 	}
 
+	private getExternalEditorCommand(): string | undefined {
+		const editorCmd = this.externalEditorCommand || process.env.VISUAL || process.env.EDITOR;
+		if (editorCmd) {
+			return editorCmd;
+		}
+		return process.platform === "win32" ? "notepad" : "nano";
+	}
+
 	private async openExternalEditor(): Promise<void> {
-		const editorCmd = process.env.VISUAL || process.env.EDITOR;
+		const editorCmd = this.getExternalEditorCommand();
 		if (!editorCmd) {
 			return;
 		}

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -2239,6 +2239,8 @@ export class InteractiveMode {
 					this.hideExtensionEditor();
 					resolve(undefined);
 				},
+				undefined,
+				this.settingsManager.getExternalEditorCommand(),
 			);
 
 			this.editorContainer.clear();
@@ -3647,10 +3649,9 @@ export class InteractiveMode {
 	}
 
 	private async openExternalEditor(): Promise<void> {
-		// Determine editor (respect $VISUAL, then $EDITOR)
-		const editorCmd = process.env.VISUAL || process.env.EDITOR;
+		const editorCmd = this.settingsManager.getExternalEditorCommand();
 		if (!editorCmd) {
-			this.showWarning("No editor configured. Set $VISUAL or $EDITOR environment variable.");
+			this.showWarning("No editor configured. Set externalEditor in settings.json or $VISUAL/$EDITOR.");
 			return;
 		}