chore: Update agent instructions and retry limit in plugin_reflect_tool_retry sample

The agent's instructions are updated to guide it to guess a positive integer, starting from 50 and decreasing, using the `guess_number_tool` until the target is found. The maximum number of retries for the `CustomRetryPlugin` is increased from 6 to 10.

Co-authored-by: Hangfei Lin <hangfei@google.com>
PiperOrigin-RevId: 830984481

contributing/samples/plugin_reflect_tool_retry/basic/agent.py

@@ -56,10 +56,17 @@ class CustomRetryPlugin(ReflectAndRetryToolPlugin):
     return result if result.get("status") == "error" else None
 
 
+# Sample query: "guess a number between 1 and 50"
 root_agent = LlmAgent(
     name="hello_world",
     description="Helpful agent",
-    instruction="""Use guess_number_tool to guess a number.""",
+    instruction="""Your goal is to guess a secret positive integer by using the
+    `guess_number_tool`.
+    The tool will provide feedback on each guess.
+    Your objective is to keep guessing until guess_number_tool returns
+    'status: success'.
+    Start by guessing 50, and use the tool's feedback to adjust your guesses
+    and find the target number.""",
     model="gemini-2.5-flash",
     tools=[guess_number_tool],
 )
@@ -70,7 +77,7 @@ app = App(
     root_agent=root_agent,
     plugins=[
         CustomRetryPlugin(
-            max_retries=6, throw_exception_if_retry_exceeded=False
+            max_retries=20, throw_exception_if_retry_exceeded=False
         ),
         LoggingPlugin(),
     ],