Function validate_state_key 

pub fn validate_state_key(key: &str) -> Result<(), &'static str>

Core traits and types.

Always available regardless of feature flags. Includes:

• Agent - The fundamental trait for all agents
• Tool / Toolset - For extending agents with capabilities
• Session / State - For managing conversation context
• Event - For streaming agent responses
• AdkError / Result - Unified error handling Validates a state key. Returns Ok(()) if the key is safe, or an error message.

Rules:

• Must not be empty
• Must not exceed MAX_STATE_KEY_LEN bytes
• Must not contain path separators (/, \) or ..
• Must not contain null bytes