fix(tui): applied follow-up slash commands

Route follow-up shortcut submissions through the builtin slash-command dispatcher before queueing them as deferred prompts.

Added regression coverage for /goal set submitted through InputController.handleFollowUp while a stream is active.

Fixes #2038

packages/coding-agent/src/modes/controllers/input-controller.ts

@@ -589,7 +589,7 @@ export class InputController {
 
 	/** Send editor text as a follow-up message (queued behind current stream). */
 	async handleFollowUp(): Promise<void> {
-		const text = this.ctx.editor.getText().trim();
+		let text = this.ctx.editor.getText().trim();
 		if (!text) return;
 
 		// Compaction first: while compacting, free text gets queued via
@@ -603,6 +603,16 @@ export class InputController {
 			return;
 		}
 
+		const slashResult = await executeBuiltinSlashCommand(text, {
+			ctx: this.ctx,
+		});
+		if (slashResult === true) {
+			return;
+		}
+		if (typeof slashResult === "string") {
+			text = slashResult;
+		}
+
 		// Skill commands invoke through the custom-message path regardless of
 		// which keybinding submitted them. Enter routes them as `steer`;
 		// Ctrl+Enter (this handler) routes them as `followUp`.