Parent: #6871 | Epic: #6870

Description

Create new agent implementation backed by copilot.Session instead of langchaingo, and a factory to construct it. These implement the existing Agent interface so call sites can switch without API changes.

Tasks

• Create internal/agent/copilot_agent.go implementing Agent interface
  • SendMessage(ctx, message) → session.SendAndWait(ctx, MessageOptions{Prompt: message})
  • SendMessageWithRetry(ctx, message) → retry wrapper around SendMessage
  • Event subscription via session.On(SessionEventHandler)
• Create internal/agent/copilot_agent_factory.go
  • Create copilot.Client via CopilotClientManager
  • Build SessionConfig via config bridge
  • Configure SessionHooks: PreToolUse, PostToolUse, ErrorOccurred
  • Configure PermissionHandler for interactive tool approval
  • Configure MCPServers from merged config
  • Wire SDK event handlers for logging
• Unit tests for both

New Files

• internal/agent/copilot_agent.go
• internal/agent/copilot_agent_factory.go

Notes

• Must implement same Agent interface as existing ConversationalAzdAiAgent
• SDK permission hooks replace entire consent system (PermissionHandler, PreToolUseHandler, AvailableTools/ExcludedTools)
• MCP servers loaded via SessionConfig.MCPServers (both stdio and http)
• No custom tools registered — Copilot CLI provides file I/O, search, command execution built-in
• 11 azd-specific guidance tools served via azd mcp start MCP server