feat: GitHub Copilot CLI integration — hooks, agents, MCP, skills

[bilersan]

Summary

Full GitHub Copilot CLI integration for ctx, enabling persistent AI context management within the Copilot CLI ecosystem. This brings ctx's context system (.context/ files, session recall, drift detection) to GitHub Copilot CLI users with the same level of support as Claude Code and VS Code Copilot.

What's Included

Phase 1 — Hook Generation (cross-platform)

• ctx hook copilot-cli --write generates .github/hooks/ctx-hooks.json
• Dual bash/PowerShell scripts for all lifecycle events: sessionStart, preToolUse, postToolUse, sessionEnd
• Dangerous command blocking in preToolUse hooks
• Per-hook timeout control and working directory configuration

Phase 2 — Agent Instructions & Extras

• AGENTS.md generation (ctx hook agents --write) with universal agent instructions
• .github/agents/ctx.md — custom Copilot CLI agent for context delegation
• .github/instructions/context.instructions.md — path-specific instructions for .context/ files
• Marker-based idempotent merge with existing files

Phase 3 — MCP Registration & Session Parser

• Auto-register ctx MCP server in ~/.copilot/mcp-config.json (respects COPILOT_HOME)
• Merge-safe config: reads existing config, adds ctx server entry, writes back
• CopilotCLIParser implementing SessionParser interface for ctx recall
• Cross-platform session directory detection (macOS, Linux, Windows)

Phase 4 — Copilot CLI Skills

• 5 skill templates in .github/skills/<name>/SKILL.md:
  • ctx-status — context summary and health check
  • ctx-recall — session history browsing
  • ctx-drift — context drift detection
  • ctx-compact — archive completed tasks
  • ctx-next — advance to next task
• YAML frontmatter format matching Copilot CLI skill spec
• Embedded in ctx binary, written alongside hooks by --write

Feature Matrix

See full comparison: specs/copilot-cli-integration.md

Category	Claude Code	VS Code	Copilot CLI
Context Injection	✅ 6/6	✅ 4/6	✅ 5/6
Hook System	✅ 5/15	✅ 1/15	✅ 10/15
MCP Server (11 tools)	✅	✅	✅
Session Recall	✅ 5/7	✅ 5/7	✅ 5/7
Skills	✅ 37	—	✅ 5
Cross-Platform	✅ 6/9	✅ 8/9	✅ 9/9

Deferred (Future Work)

• ACP (Agent Client Protocol) server mode
• Copilot Memory ↔ ctx memory bridge
• Additional lifecycle events (agentStop, subagentStop, errorOccurred)
• Full session parser implementation (pending Copilot CLI session format stabilization)