fix(exec): replace unwrap with proper error handling for client access

[echobt]

Problem

The get_or_create_client method in cortex-exec/src/runner.rs line 198 contained an unsafe .unwrap() call:

Ok(self.client.as_ref().unwrap().as_ref())

This could panic at runtime if the client field is None, leading to an unrecoverable crash.

Solution

Replaced the unsafe .unwrap() with proper error handling that returns a descriptive CortexError::Internal when the client is not initialized:

self.client
    .as_ref()
    .map(|c| c.as_ref())
    .ok_or_else(|| CortexError::Internal("LLM client not initialized".to_string()))

This approach:

• Prevents runtime panics
• Provides a clear error message for debugging
• Follows Rust best practices for error handling
• Maintains the same return type (Result<&dyn ModelClient, CortexError>)

Testing

• Verified compilation with cargo check -p cortex-exec

[echobt]

Consolidated into #73 - fix: consolidated error handling improvements