Fix(noninteractive) - Add message when user uses deprecated flag (#11682)

Co-authored-by: gemini-cli-robot <gemini-cli-robot@google.com>

packages/cli/src/nonInteractiveCli.ts

@@ -42,12 +42,21 @@ import {
 } from './utils/errors.js';
 import { TextOutput } from './ui/utils/textOutput.js';
 
-export async function runNonInteractive(
-  config: Config,
-  settings: LoadedSettings,
-  input: string,
-  prompt_id: string,
-): Promise<void> {
+interface RunNonInteractiveParams {
+  config: Config;
+  settings: LoadedSettings;
+  input: string;
+  prompt_id: string;
+  hasDeprecatedPromptArg?: boolean;
+}
+
+export async function runNonInteractive({
+  config,
+  settings,
+  input,
+  prompt_id,
+  hasDeprecatedPromptArg,
+}: RunNonInteractiveParams): Promise<void> {
   return promptIdContext.run(prompt_id, async () => {
     const consolePatcher = new ConsolePatcher({
       stderr: true,
@@ -151,6 +160,21 @@ export async function runNonInteractive(
       let currentMessages: Content[] = [{ role: 'user', parts: query }];
 
       let turnCount = 0;
+      const deprecateText =
+        'The --prompt (-p) flag has been deprecated and will be removed in a future version. Please use a positional argument for your prompt. See gemini --help for more information.\n';
+      if (hasDeprecatedPromptArg) {
+        if (streamFormatter) {
+          streamFormatter.emitEvent({
+            type: JsonStreamEventType.MESSAGE,
+            timestamp: new Date().toISOString(),
+            role: 'assistant',
+            content: deprecateText,
+            delta: true,
+          });
+        } else {
+          process.stderr.write(deprecateText);
+        }
+      }
       while (true) {
         turnCount++;
         if (