Add get_by_id method to Agent class

[devin-ai-integration]

Add get_by_id method to Agent class

Summary

Adds a new get_by_id method to the Agent class in vlmrun/client/agent.py that retrieves agent information by ID. The method makes a GET request to /agents/{agent_id} and returns an AgentInfo object, following the same implementation pattern as other methods in the class.

This change is part of a coordinated implementation with vlm-lab (PR #941) that adds the corresponding backend endpoint.

Key changes:

• New get_by_id(agent_id: str) -> AgentInfo method in Agent class
• Uses the same HTTP request pattern as existing methods
• Proper type annotations and error handling following class conventions

Review & Testing Checklist for Human

• End-to-end functionality: Test client.agent.get_by_id("test-id") against a running vlm-lab instance to verify it works correctly
• URL format verification: Confirm that the SDK's agents/{agent_id} URL pattern matches the backend route /agents/{agent_id} exactly
• Error handling: Test with invalid agent IDs, empty strings, and special characters to ensure proper error responses
• Return type verification: Verify that the returned AgentInfo object contains the expected fields and structure

Recommended test plan:

1. Start vlm-lab server locally and install this SDK version
2. Test: client.agent.get_by_id("test-123") and verify response structure
3. Test edge cases: empty string, special characters, very long IDs
4. Compare response format with client.agent.get() to ensure consistency

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    ClientCode["Client Application"]:::context
    AgentClass["vlmrun/client/<br/>agent.py"]:::major-edit  
    AgentInfo["AgentInfo<br/>Response Model"]:::context
    APIEndpoint["GET /agents/{agent_id}<br/>(vlm-lab backend)"]:::context
    
    ClientCode -->|"get_by_id(agent_id)"| AgentClass
    AgentClass -->|"HTTP GET request"| APIEndpoint
    APIEndpoint -->|"JSON response"| AgentClass
    AgentClass -->|"returns"| AgentInfo
    
    subgraph Legend
        L1["Major Edit"]:::major-edit
        L2["Minor Edit"]:::minor-edit  
        L3["Context/No Edit"]:::context
    end
    
    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB  
    classDef context fill:#FFFFFF

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Notes

• Pattern consistency: Implementation follows the same structure as existing get() method in the Agent class
• Integration testing limitation: Could not fully test end-to-end during development due to SDK dependency issues in vlm-lab test environment
• Coordinated change: This SDK change works together with vlm-lab PR #941 that implements the backend endpoint
• Type safety: Proper type annotations ensure IDE support and runtime validation

Link to Devin run: https://app.devin.ai/sessions/57de09ce83e7430599fd797e49db9670
Requested by: Sudeep Pillai (@spillai)

[devin-ai-integration]

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