[BUG] Built-in ask_user accepts empty or blank questions #2468

📋 Prerequisites

• I have searched the existing issues to avoid creating a duplicate
• By submitting this issue, you agree to follow our Code of Conduct
• I am using the latest version of the software
• I have tried to clear cache/cookies or used incognito mode (if ui-related)
• I can consistently reproduce this issue

🎯 Affected Service(s)

Multiple services / System-wide issue

🚦 Impact/Severity

Minor inconvenience

🐛 Bug Description

The built-in ask_user tool in both the Go and Python ADK runtimes accepts an empty questions list. It also accepts question entries whose question text is empty or contains only whitespace. These invalid inputs can request confirmation without presenting a usable question.

🔄 Steps To Reproduce

1. Invoke the built-in ask_user tool in either runtime with {"questions": []}.
2. Observe that a confirmation request is created without a usable question.
3. Invoke it with a single question whose text is empty, for example {"questions": [{"question": ""}]}.
4. Repeat with whitespace-only question text and observe the same behavior.

🤔 Expected Behavior

The tool should reject an empty question list and any question with empty or whitespace-only text before requesting confirmation. Valid single-question behavior should remain unchanged: the initial invocation should request confirmation, and a confirmed invocation should return the answer normally.

📱 Actual Behavior

Both runtimes can request confirmation for an empty question list or blank question text, producing an unusable interaction.

💻 Environment

• Current kagent release
• Go and Python ADK runtimes

🔧 CLI Bug Report

Not applicable

🔍 Additional Context

Validation should be consistent in both runtimes and occur before the confirmation API is called.

📋 Logs

📷 Screenshots

Not applicable

🙋 Are you willing to contribute?

• I am willing to submit a PR to fix this issue