feat: Add GitHub Copilot converter target

Add Copilot as the 6th converter target, transforming Claude Code plugins into Copilot's native format: custom agents (.agent.md), agent skills (SKILL.md), and MCP server configuration JSON. Component mapping: - Agents → .github/agents/{name}.agent.md (with Copilot frontmatter) - Commands → .github/skills/{name}/SKILL.md - Skills → .github/skills/{name}/ (copied as-is) - MCP servers → .github/copilot-mcp-config.json - Hooks → skipped with warning Also adds `compound sync copilot` support and fixes YAML quoting for the `*` character in frontmatter serialization. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-02-15 00:14:40 -03:00
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+---
+title: "feat: Add GitHub Copilot converter target"
+type: feat
+date: 2026-02-14
+status: complete
+---
+
+# feat: Add GitHub Copilot Converter Target
+
+## Overview
+
+Add GitHub Copilot as a converter target following the established `TargetHandler` pattern. This converts the compound-engineering Claude Code plugin into Copilot's native format: custom agents (`.agent.md`), agent skills (`SKILL.md`), and MCP server configuration JSON.
+
+**Brainstorm:** `docs/brainstorms/2026-02-14-copilot-converter-target-brainstorm.md`
+
+## Problem Statement
+
+The CLI tool (`compound`) already supports converting Claude Code plugins to 5 target formats (OpenCode, Codex, Droid, Cursor, Pi). GitHub Copilot is a widely-used AI coding assistant that now supports custom agents, skills, and MCP servers — but there's no converter target for it.
+
+## Proposed Solution
+
+Follow the existing converter pattern exactly:
+
+1. Define types (`src/types/copilot.ts`)
+2. Implement converter (`src/converters/claude-to-copilot.ts`)
+3. Implement writer (`src/targets/copilot.ts`)
+4. Register target (`src/targets/index.ts`)
+5. Add sync support (`src/sync/copilot.ts`, `src/commands/sync.ts`)
+6. Write tests and documentation
+
+### Component Mapping
+
+| Claude Code | Copilot | Output Path |
+|-------------|---------|-------------|
+| Agents (`.md`) | Custom Agents (`.agent.md`) | `.github/agents/{name}.agent.md` |
+| Commands (`.md`) | Agent Skills (`SKILL.md`) | `.github/skills/{name}/SKILL.md` |
+| Skills (`SKILL.md`) | Agent Skills (`SKILL.md`) | `.github/skills/{name}/SKILL.md` |
+| MCP Servers | Config JSON | `.github/copilot-mcp-config.json` |
+| Hooks | Skipped | Warning to stderr |
+
+## Technical Approach
+
+### Phase 1: Types
+
+**File:** `src/types/copilot.ts`
+
+```typescript
+export type CopilotAgent = {
+  name: string
+  content: string // Full .agent.md content with frontmatter
+}
+
+export type CopilotGeneratedSkill = {
+  name: string
+  content: string // SKILL.md content with frontmatter
+}
+
+export type CopilotSkillDir = {
+  name: string
+  sourceDir: string
+}
+
+export type CopilotMcpServer = {
+  type: string
+  command?: string
+  args?: string[]
+  url?: string
+  tools: string[]
+  env?: Record<string, string>
+  headers?: Record<string, string>
+}
+
+export type CopilotBundle = {
+  agents: CopilotAgent[]
+  generatedSkills: CopilotGeneratedSkill[]
+  skillDirs: CopilotSkillDir[]
+  mcpConfig?: Record<string, CopilotMcpServer>
+}
+```
+
+### Phase 2: Converter
+
+**File:** `src/converters/claude-to-copilot.ts`
+
+**Agent conversion:**
+- Frontmatter: `description` (required, fallback to `"Converted from Claude agent {name}"`), `tools: ["*"]`, `infer: true`
+- Pass through `model` if present
+- Fold `capabilities` into body as `## Capabilities` section (same as Cursor)
+- Use `formatFrontmatter()` utility
+- Warn if body exceeds 30,000 characters (`.length`)
+
+**Command → Skill conversion:**
+- Convert to SKILL.md format with frontmatter: `name`, `description`
+- Flatten namespaced names: `workflows:plan` → `plan`
+- Drop `allowed-tools`, `model`, `disable-model-invocation` silently
+- Include `argument-hint` as `## Arguments` section in body
+
+**Skill pass-through:**
+- Map to `CopilotSkillDir` as-is (same as Cursor)
+
+**MCP server conversion:**
+- Transform env var names: `API_KEY` → `COPILOT_MCP_API_KEY`
+- Skip vars already prefixed with `COPILOT_MCP_`
+- Add `type: "local"` for command-based servers, `type: "sse"` for URL-based
+- Set `tools: ["*"]` for all servers
+
+**Content transformation (`transformContentForCopilot`):**
+
+| Pattern | Input | Output |
+|---------|-------|--------|
+| Task calls | `Task repo-research-analyst(desc)` | `Use the repo-research-analyst skill to: desc` |
+| Slash commands | `/workflows:plan` | `/plan` |
+| Path rewriting | `.claude/` | `.github/` |
+| Home path rewriting | `~/.claude/` | `~/.copilot/` |
+| Agent references | `@security-sentinel` | `the security-sentinel agent` |
+
+**Hooks:** Warn to stderr if present, skip.
+
+### Phase 3: Writer
+
+**File:** `src/targets/copilot.ts`
+
+**Path resolution:**
+- If `outputRoot` basename is `.github`, write directly into it (avoid `.github/.github/` double-nesting)
+- Otherwise, nest under `.github/`
+
+**Write operations:**
+- Agents → `.github/agents/{name}.agent.md` (note: `.agent.md` extension)
+- Generated skills (from commands) → `.github/skills/{name}/SKILL.md`
+- Skill dirs → `.github/skills/{name}/` (copy via `copyDir`)
+- MCP config → `.github/copilot-mcp-config.json` (backup existing with `backupFile`)
+
+### Phase 4: Target Registration
+
+**File:** `src/targets/index.ts`
+
+Add import and register:
+
+```typescript
+import { convertClaudeToCopilot } from "../converters/claude-to-copilot"
+import { writeCopilotBundle } from "./copilot"
+
+// In targets record:
+copilot: {
+  name: "copilot",
+  implemented: true,
+  convert: convertClaudeToCopilot as TargetHandler<CopilotBundle>["convert"],
+  write: writeCopilotBundle as TargetHandler<CopilotBundle>["write"],
+},
+```
+
+### Phase 5: Sync Support
+
+**File:** `src/sync/copilot.ts`
+
+Follow the Cursor sync pattern (`src/sync/cursor.ts`):
+- Symlink skills to `.github/skills/` using `forceSymlink`
+- Validate skill names with `isValidSkillName`
+- Convert MCP servers with `COPILOT_MCP_` prefix transformation
+- Merge MCP config into existing `.github/copilot-mcp-config.json`
+
+**File:** `src/commands/sync.ts`
+
+- Add `"copilot"` to `validTargets` array
+- Add case in `resolveOutputRoot()`: `case "copilot": return path.join(process.cwd(), ".github")`
+- Add import and switch case for `syncToCopilot`
+- Update meta description to include "Copilot"
+
+### Phase 6: Tests
+
+**File:** `tests/copilot-converter.test.ts`
+
+Test cases (following `tests/cursor-converter.test.ts` pattern):
+
+```
+describe("convertClaudeToCopilot")
+  ✓ converts agents to .agent.md with Copilot frontmatter
+  ✓ agent description is required, fallback generated if missing
+  ✓ agent with empty body gets default body
+  ✓ agent capabilities are prepended to body
+  ✓ agent model field is passed through
+  ✓ agent tools defaults to ["*"]
+  ✓ agent infer defaults to true
+  ✓ warns when agent body exceeds 30k characters
+  ✓ converts commands to skills with SKILL.md format
+  ✓ flattens namespaced command names
+  ✓ command name collision after flattening is deduplicated
+  ✓ command allowedTools is silently dropped
+  ✓ command with argument-hint gets Arguments section
+  ✓ passes through skill directories
+  ✓ skill and generated skill name collision is deduplicated
+  ✓ converts MCP servers with COPILOT_MCP_ prefix
+  ✓ MCP env vars already prefixed are not double-prefixed
+  ✓ MCP servers get type field (local vs sse)
+  ✓ warns when hooks are present
+  ✓ no warning when hooks are absent
+  ✓ plugin with zero agents produces empty agents array
+  ✓ plugin with only skills works
+
+describe("transformContentForCopilot")
+  ✓ rewrites .claude/ paths to .github/
+  ✓ rewrites ~/.claude/ paths to ~/.copilot/
+  ✓ transforms Task agent calls to skill references
+  ✓ flattens slash commands
+  ✓ transforms @agent references to agent references
+```
+
+**File:** `tests/copilot-writer.test.ts`
+
+Test cases (following `tests/cursor-writer.test.ts` pattern):
+
+```
+describe("writeCopilotBundle")
+  ✓ writes agents, generated skills, copied skills, and MCP config
+  ✓ agents use .agent.md file extension
+  ✓ writes directly into .github output root without double-nesting
+  ✓ handles empty bundles gracefully
+  ✓ writes multiple agents as separate .agent.md files
+  ✓ backs up existing copilot-mcp-config.json before overwriting
+  ✓ creates skill directories with SKILL.md
+```
+
+**File:** `tests/sync-copilot.test.ts`
+
+Test cases (following `tests/sync-cursor.test.ts` pattern):
+
+```
+describe("syncToCopilot")
+  ✓ symlinks skills to .github/skills/
+  ✓ skips skills with invalid names
+  ✓ merges MCP config with existing file
+  ✓ transforms MCP env var names to COPILOT_MCP_ prefix
+  ✓ writes MCP config with restricted permissions (0o600)
+```
+
+### Phase 7: Documentation
+
+**File:** `docs/specs/copilot.md`
+
+Follow `docs/specs/cursor.md` format:
+- Last verified date
+- Primary sources (GitHub Docs URLs)
+- Config locations table
+- Agents section (`.agent.md` format, frontmatter fields)
+- Skills section (`SKILL.md` format)
+- MCP section (config structure, env var prefix requirement)
+- Character limits (30k agent body)
+
+**File:** `README.md`
+
+- Add "copilot" to the list of supported targets
+- Add usage example: `compound convert --to copilot ./plugins/compound-engineering`
+- Add sync example: `compound sync copilot`
+
+## Acceptance Criteria
+
+### Converter
+- [x] Agents convert to `.agent.md` with `description`, `tools: ["*"]`, `infer: true`
+- [x] Agent `model` passes through when present
+- [x] Agent `capabilities` fold into body as `## Capabilities`
+- [x] Missing description generates fallback
+- [x] Empty body generates fallback
+- [x] Body exceeding 30k chars triggers stderr warning
+- [x] Commands convert to SKILL.md format
+- [x] Command names flatten (`workflows:plan` → `plan`)
+- [x] Name collisions deduplicated with `-2`, `-3` suffix
+- [x] Command `allowed-tools` dropped silently
+- [x] Skills pass through as `CopilotSkillDir`
+- [x] MCP env vars prefixed with `COPILOT_MCP_`
+- [x] Already-prefixed env vars not double-prefixed
+- [x] MCP servers get `type` field (`local` or `sse`)
+- [x] Hooks trigger warning, skip conversion
+- [x] Content transformation: Task calls, slash commands, paths, @agent refs
+
+### Writer
+- [x] Agents written to `.github/agents/{name}.agent.md`
+- [x] Generated skills written to `.github/skills/{name}/SKILL.md`
+- [x] Skill dirs copied to `.github/skills/{name}/`
+- [x] MCP config written to `.github/copilot-mcp-config.json`
+- [x] Existing MCP config backed up before overwrite
+- [x] No double-nesting when outputRoot is `.github`
+- [x] Empty bundles handled gracefully
+
+### CLI Integration
+- [x] `compound convert --to copilot` works
+- [x] `compound sync copilot` works
+- [x] Copilot registered in `src/targets/index.ts`
+- [x] Sync resolves output to `.github/` in current directory
+
+### Tests
+- [x] `tests/copilot-converter.test.ts` — all converter tests pass
+- [x] `tests/copilot-writer.test.ts` — all writer tests pass
+- [x] `tests/sync-copilot.test.ts` — all sync tests pass
+
+### Documentation
+- [x] `docs/specs/copilot.md` — format specification
+- [x] `README.md` — updated with copilot target
+
+## Files to Create
+
+| File | Purpose |
+|------|---------|
+| `src/types/copilot.ts` | Type definitions |
+| `src/converters/claude-to-copilot.ts` | Converter logic |
+| `src/targets/copilot.ts` | Writer logic |
+| `src/sync/copilot.ts` | Sync handler |
+| `tests/copilot-converter.test.ts` | Converter tests |
+| `tests/copilot-writer.test.ts` | Writer tests |
+| `tests/sync-copilot.test.ts` | Sync tests |
+| `docs/specs/copilot.md` | Format specification |
+
+## Files to Modify
+
+| File | Change |
+|------|--------|
+| `src/targets/index.ts` | Register copilot target |
+| `src/commands/sync.ts` | Add copilot to valid targets, output root, switch case |
+| `README.md` | Add copilot to supported targets |
+
+## References
+
+- [Custom agents configuration - GitHub Docs](https://docs.github.com/en/copilot/reference/custom-agents-configuration)
+- [About Agent Skills - GitHub Docs](https://docs.github.com/en/copilot/concepts/agents/about-agent-skills)
+- [MCP and coding agent - GitHub Docs](https://docs.github.com/en/copilot/concepts/agents/coding-agent/mcp-and-coding-agent)
+- Existing converter: `src/converters/claude-to-cursor.ts`
+- Existing writer: `src/targets/cursor.ts`
+- Existing sync: `src/sync/cursor.ts`
+- Existing tests: `tests/cursor-converter.test.ts`, `tests/cursor-writer.test.ts`