Parent Epic: #6870

Overview

Add the GitHub Copilot SDK dependency and build the new client/session infrastructure alongside existing langchaingo code. No existing code is modified or deleted in this phase.

Approach

All new files are created next to existing implementations. Both langchaingo and Copilot SDK agent implementations coexist. Build must pass with both present.

Child Issues

See linked child issues for individual work items:

• Add copilot-sdk Go dependency
• Create CopilotClientManager
• Create config → SessionConfig bridge
• Create CopilotAgent implementation
• Create CopilotAgentFactory
• Create SDK event handlers
• Add agent config options

Acceptance Criteria

• go build succeeds with both implementations present
• New agent can be instantiated (even if not wired to call sites)
• Config options are documented and functional
• Unit tests for new code