# 06 — Config System

`harness-core/src/config/`.

## Locations & precedence (lowest → highest)

1. Bundled defaults (compiled in)
2. Global: `~/.config/ai-harness/config.json`
3. Project chain: walk up from cwd collecting `.harness/config.json`, apply root-most first
4. Env overrides (`AI_HARNESS_MODEL`, `AI_HARNESS_CONFIG`, provider key env vars)

JSONC via `jsonc-parser` (comments + trailing commas). Deep-merge objects, replace arrays. After merge: string interpolation of `{env:VAR}` and `{file:path}` (the latter useful for prompts).

## Schema

```rust
pub struct Config {
    pub model: Option<String>,                    // "anthropic/claude-sonnet-4-5"
    pub small_model: Option<String>,              // titles/summaries/compaction
    pub providers: HashMap<String, ProviderConfig>,  // { enabled, api_key, base_url }
    pub agents: HashMap<String, AgentPatch>,      // patch semantics over loaded agent defs
    pub permissions: Vec<Rule>,                   // ordered; last-match-wins
    pub orchestration: OrchestrationConfig,       // { depth_limit: 3, job_board: true,
                                                  //   max_reusable_per_agent: 2, reminders: None }
    pub mcp: HashMap<String, McpServerConfig>,    // { command, args, env, enabled }
    pub lsp: HashMap<String, LspServerConfig>,    // { command, args, extensions: ["rs"] }
    pub tui: TuiConfig,                           // theme; keybinds later
    pub instructions: Vec<String>,                // files appended to system prompt (AGENTS.md, ...)
}

pub struct Rule { pub permission: String, pub pattern: String, pub action: Action }
```

Example:

```jsonc
{
  "model": "github-copilot/claude-sonnet-4.5",
  "small_model": "openai/gpt-4o-mini",
  "providers": {
    "anthropic": { "api_key": "{env:ANTHROPIC_API_KEY}" }
  },
  "agents": {
    "explorer": { "model": "github-copilot/gpt-4o", "temperature": 0 },
    "designer": { "disable": true },
    // unknown key + prompt/model → custom agent
    "reviewer": { "mode": "subagent", "prompt": "{file:./prompts/reviewer.md}" }
  },
  "permissions": [
    { "permission": "bash", "pattern": "git status*", "action": "allow" },
    { "permission": "edit", "pattern": "*.lock", "action": "deny" }
  ],
  "mcp": {
    "context7": { "command": "npx", "args": ["-y", "@upstash/context7-mcp"] }
  }
}
```

## Markdown asset loading (`config/markdown.rs`)

All three kinds use YAML frontmatter + markdown body, from `~/.config/ai-harness/<kind>/` (global) and `<project>/.harness/<kind>/` (project wins by name):

- **Agents** — `agent/*.md` → `AgentDef` (see [04-multiagent.md](04-multiagent.md)).
- **Commands** — `command/*.md` → `CommandDef { name (filename), description, agent?, model?, template }`. Invoked as `/name args` in the TUI; template substitutes `$ARGUMENTS` / `$1..$9` and becomes the user message, optionally switching agent/model for that run.
- **Skills** — `skill/<name>/SKILL.md` → advertised (name + description) in a system prompt section; the full body is fetched on demand via the built-in `skill` tool.