Earendil Pi
Pi 1.0 ships MCP in core; experimental Pi Durable harness over pluggable storage
Pi is a minimal agent harness. At 1.0 it ships MCP in core via its codemode sandbox. Earendil’s stated reason: MCP should behave more like OpenAPI, with structured returns and discovery by documentation, not by dumping tools into context. The same cycle introduced experimental MIT-licensed Pi Durable: a harness over pluggable storage (memory, SQLite, JSONL, plus a conformance suite) for long-running agents that survive crashes, can be reached from several surfaces, and let several humans steer the same agent. About 15,000 lines so an agent can read it. Pick harness storage you control, keep tool returns structured, and treat durable sessions as long-lived principals for revocation. Durable storage must sit outside the agent’s write permissions — see /playbooks/harness-permission-outside-agent/. Primaries: https://earendil.com/posts/you-said-no-mcp/ ; https://earendil.com/posts/pi-durable/.
Use Cases
- Run Pi 1.0 with MCP in core through the codemode sandbox
- Keep MCP tool returns structured and discoverable from documentation
- Open an experimental Pi Durable harness over memory, SQLite, or JSONL storage
- Keep a long-running agent reachable from several surfaces after a crash
- Let several humans steer the same agent while treating the session as a revocable principal
Key Features
MCP in core via codemode
Pi 1.0 ships MCP in core through its codemode sandbox. Earendil’s stated reason: MCP should behave more like OpenAPI, with structured returns and discovery by documentation, not by dumping tools into context.
Codemode sandbox
Codemode is a harness-side JavaScript sandbox for composing tool calls. In Pi it loads automatically when MCP is configured, or can be added as a default tool.
Pi Durable (experimental, MIT-licensed)
A harness over pluggable storage for long-running agents that survive crashes, can be reached from several surfaces, and let several humans steer the same agent. About 15,000 lines so an agent can read it.
Pluggable storage plus conformance suite
Pi Durable ships memory, SQLite, and JSONL storage, plus a conformance suite for additional backends. Pick storage you control; keep it outside the agent’s write permissions.
Durable sessions as principals
Treat durable sessions as long-lived principals for revocation. Continuity helps operators; it does not make a host-local transcript an audit trail.