/writers-pattern

name: writers-pattern
description: Add a new platform writer module in src/writers/ that generates and writes agent config files for a supported platform. Each writer exports a function that accepts a config interface, creates directories (rules/, skills/, mcp configs), writes files with proper formatting and frontmatter, and returns string[] of written file paths. Use when adding platform support for a new agent, integrating a new code AI tool, or extending caliber to support new targets. Do NOT use for modifying existing writers, refactoring scoring logic, or changing how writers are invoked.
paths:
  - src/writers/*/index.ts
  - src/writers/__tests__/*.test.ts
  - src/writers/index.ts

Platform Writer Pattern

Critical

• **Every writer MUST**:

1. Export a single named function: `write<Platform>Config(config: <PlatformConfig>): string[]` 2. Accept a platform-specific config interface defining what content to write 3. Return `string[]` of all written file paths (used by manifest and progress display) 4. Create parent directories with `fs.mkdirSync(dir, { recursive: true })` before writing files 5. Wrap skill frontmatter exactly as shown in Step 4 (YAML between `---` markers) 6. NOT modify files outside the intended platform directories (e.g., Claude writer only touches `.claude/`, `CLAUDE.md`, `.mcp.json`)

• **Integration point**: Every writer MUST be imported and called in `src/writers/index.ts` within the `writeSetup()` function. Missing this step means the writer will never execute.

• **Validation before Step 1**: Verify the platform name is unique (`ls src/writers/` shows no `<platform>/index.ts`). If it exists, you are modifying, not adding.

Instructions

Step 1: Define the Platform Config Interface

Verify the platform name is unique (see Critical). Create `src/writers/<platform>/index.ts`.

At the top of the file, define a config interface that describes all content the writer accepts. The interface MUST include:

• A main markdown/text file (e.g., `claudeMd`, `cursorrules`, `agentsMd`, `instructions`)
• Optional nested arrays: `rules`, `skills`, `mcpServers`, `instructionFiles`, etc.
• Each rule/skill/file has at minimum: `name` or `filename`, `content`, and for skills, `description`

Example (matching GitHub Copilot pattern already in codebase):

interface CopilotConfig {
  instructions: string;  // Main content
  instructionFiles?: Array<{ filename: string; content: string }>;
}

**Validation**: Confirm the interface property names match platform conventions (e.g., Claude uses `claudeMd`, Cursor uses `cursorrules`). Check existing writers: `src/writers/claude/index.ts` line 9, `src/writers/cursor/index.ts` line 9, `src/writers/codex/index.ts` line 5.

Step 2: Implement the Writer Export Function

Export a function named `write<Platform>Config(config: <PlatformConfig>): string[]` that:

1. Initialize an empty `written: string[] = []` array to track all written paths. 2. For the **main config file** (e.g., `CLAUDE.md` for Claude, `.cursorrules` for Cursor):

• Wrap the content with **platform-specific blocks**: Use helpers from `src/writers/pre-commit-block.ts`
• Common blocks: `appendPreCommitBlock(content, platform)`, `appendLearningsBlock(content)`, `appendSyncBlock(content)`
• Examples from actual codebase:
• **Claude** (`src/writers/claude/index.ts` line 19-22): `appendSyncBlock(appendLearningsBlock(appendPreCommitBlock(config.claudeMd)))`
• **Cursor** (`src/writers/cursor/index.ts` line 19-22): No sync block; injects rules instead (pre-commit, learnings, sync as separate files)
• **Codex** (`src/writers/codex/index.ts` line 13-16): `appendLearningsBlock(appendPreCommitBlock(config.agentsMd, 'codex'))`
• **Copilot** (`src/writers/github-copilot/index.ts` line 19-22): `appendSyncBlock(appendLearningsBlock(appendPreCommitBlock(config.instructions, 'copilot')))`
• Write to the exact path (e.g., `fs.writeFileSync('CLAUDE.md', wrappedContent)`) and push to `written`.

3. For **rules** (if applicable): Platform convention determines directory.

• Cursor uses `.cursor/rules/`, Claude uses `.claude/rules/` (see `src/writers/index.ts` lines 123-126 and 135-137)
• For each rule: create the directory, write to `<dir>/<rule.filename>`, push path to `written`
• **Cursor special case** (`src/writers/cursor/index.ts` line 24-27): Cursor injects three system rules:

     const preCommitRule = getCursorPreCommitRule();
     const learningsRule = getCursorLearningsRule();
     const syncRule = getCursorSyncRule();
     const allRules = [...(config.rules || []), preCommitRule, learningsRule, syncRule];

4. For **skills**: Write with YAML frontmatter.

• Directory pattern: `.claude/skills/<skillName>/SKILL.md`, `.cursor/skills/<skillName>/SKILL.md`, `.agents/skills/<skillName>/SKILL.md`, `.opencode/skills/<skillName>/SKILL.md`
• Frontmatter format (exact indentation from `src/writers/claude/index.ts` line 40-47):

     ---
     name: <skill.name>
     description: <skill.description>
     paths:
       - <optional path pattern 1>
       - <optional path pattern 2>
     ---
     <skill.content>

• For **Opencode** (`src/writers/opencode/index.ts` line 30): Use `buildSkillContent(skill)` from `src/lib/builtin-skills.js` instead of manual frontmatter.
• Create directory with `fs.mkdirSync(skillDir, { recursive: true })`, write skill, push to `written`

5. For **MCP Servers** (if applicable): Write/merge JSON at platform-specific path.

• **Claude** (`src/writers/claude/index.ts` line 54-65): `.mcp.json` at root
• **Cursor** (`src/writers/cursor/index.ts` line 54-69): `.cursor/mcp.json`
• Pattern: Read existing servers (if file exists, try to parse JSON with try/catch), merge with new servers using spread operator `{ ...existingServers, ...config.mcpServers }`, write merged object
• Wrap in `{ mcpServers: mergedServers }` and output as pretty-