> ## Documentation Index
> Fetch the complete documentation index at: https://docs.runr5e.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Harness and Adapters

> Governance projected into the provider's native configuration format.

## What an Adapter Does

The adapter is a **governance-to-native-config compiler**. It takes r5e's governed session spec and projects it into whatever format the provider expects:

| r5e Input         | Claude Code Output      | Codex Output      | API Output       |
| ----------------- | ----------------------- | ----------------- | ---------------- |
| Policy grants     | `.claude/settings.json` | `--sandbox` flags | tool definitions |
| Context layers    | `CLAUDE.md`             | system prompt     | system message   |
| Tool refs         | `.claude/skills/*.md`   | tool flags        | tools array      |
| Gateway config    | MCP server config       | N/A               | base URL         |
| Credential leases | env vars (v1alpha)      | env vars          | auth headers     |
| Workspace claims  | git worktree            | `-C workdir`      | N/A              |

Same governance. Different projections. Writing a new adapter = writing a new governance projector.

## Adapter Classes

Not all adapters have the same fidelity:

| Class            | Enforcement                        | Event Fidelity                 | Example                        |
| ---------------- | ---------------------------------- | ------------------------------ | ------------------------------ |
| **opaque-cli**   | Pre-flight + observe-and-terminate | Partial (post-hoc observation) | Claude Code, Codex, Gemini CLI |
| **governed-api** | Synchronous per-call enforcement   | Full                           | Direct API adapters            |
| **governed-mcp** | MCP protocol-native enforcement    | Full                           | MCP gateway adapters           |

Downstream governance is aware of the adapter class. An opaque-cli session's audit trail has lower fidelity — this is an accepted tradeoff, not a hidden gap.

## The Adapter Contract

```elixir theme={null}
defmodule R5e.Adapter do
  @callback materialize(session_spec) :: {:ok, handle} | {:error, term}
  @callback execute(handle, event_handler) :: :ok | {:error, term}
  @callback interrupt(handle, :graceful | :hard) :: :ok | {:error, term}
  @callback report(handle) :: {:ok, result} | {:error, term}
  @callback adapter_class() :: :opaque_cli | :governed_api | :governed_mcp
end
```

Adapters are Capability resources — certified through the trust registry, governed by the same admission pipeline as everything else.