---
title: 'MCP local stdio integration roadmap'
state: 'active'
created_at: '2026-06-10T07:48:45Z'
updated_at: '2026-06-20T05:34:00Z'
linked_tickets: ['00001KTR81P9X', '00001KV0SP0TY', '00001KVHR3WRF', '00001KVHR3WRY', '00001KVHR3WS6', '00001KVHR3WSD', '00001KVHR3WSN', '00001KVHR3WSW']
---

## Objective

Add MCP local stdio integration to Yoi without weakening Worker history, prompt-context, scoped tool permission, or Plugin/Feature layering invariants.

MCP is a protocol-backed integration layer on top of `pod::feature`. `pod::feature` supplies contribution/lifecycle/runtime-discovered registration substrate; MCP owns its own enablement, local server trust model, command/env/secret policy, and MCP-specific permission decisions. MCP is not the Plugin model, and Plugin permission policy is not implemented by feature-layer authority grants.

## Strategic direction

- Baseline the initial implementation on MCP specification `2025-11-25`.
- Start with local stdio MCP servers only.
- Treat MCP server metadata, tools, resources, prompts, and results as untrusted content.
- Do not allow MCP resources/prompts to become hidden context injection.
  - They must be explicit tool operations with history records.
- Use the normal Yoi ToolRegistry, PreToolCall permission, history, and bounded result paths.
- Do not add private MCP-only bypasses around Worker/tool invariants.
- Keep sampling and elicitation fail-closed initially.
- Keep Streamable HTTP, remote auth, OAuth, and MCP Registry/distribution out of the first slice.
- Treat local stdio server execution as an explicit MCP config/trust decision, not as a `pod::feature` authority grant.
- Document clearly that a configured local MCP server runs as a local executable; Yoi feature authority does not sandbox its OS-level side effects.

## Layering decisions

- `pod::feature` is an API/contribution substrate.
  - It owns contribution declarations, provider/service lifecycle hooks, diagnostics, runtime-discovered registration plumbing, and integration with normal Worker/ToolRegistry paths.
  - It does not own Plugin permission policy or MCP server trust policy.
- Plugin is a user-facing package/config/runtime layer over `pod::feature`.
  - Plugin permissions are Plugin-layer policy.
  - Plugin package discovery/enablement must not be conflated with MCP local server execution.
- MCP is a separate feature-backed integration layer.
  - MCP enablement, command/env/secret handling, server trust, and MCP-specific permission decisions live in MCP config/implementation.
  - MCP provider-discovered tools/resources/prompts are exposed through the feature API and ordinary Yoi tool paths.

## Concrete implementation tickets

Completed prerequisites:

- `00001KTR81P9X` — Extend `pod::feature` API for external protocol-backed capability providers.
- `00001KV0SP0TY` — Remove feature-layer HostAuthority model.

Concrete MCP implementation sequence:

1. `00001KVHR3WRF` — MCP local stdio server config and trust policy.
   - explicit config, command/env/secret redaction, local executable trust boundary, no auto-start.
2. `00001KVHR3WRY` — MCP stdio JSON-RPC lifecycle client.
   - subprocess lifecycle, initialize/capability negotiation, diagnostics, shutdown.
3. `00001KVHR3WS6` — MCP tools/list registration into ToolRegistry.
   - provider-discovered tools, stable namespacing, schema validation, untrusted metadata normalization, no tools/call yet.
4. `00001KVHR3WSD` — MCP tools/call execution through ordinary Tool path.
   - PreToolCall gate before server call, bounded result serialization, history path.
5. `00001KVHR3WSN` — MCP resources/prompts as explicit tool operations.
   - resources/list/read and prompts/list/get without hidden context injection.
6. `00001KVHR3WSW` — MCP list_changed notification handling.
   - deterministic safe refresh/diagnostic behavior without breaking tool schema or prompt-cache invariants.

The old broad implementation Ticket `00001KTR82RB7` is superseded by this sequence and should not be used as an implementation work item.

## Terminology

Use `runtime-discovered` or `provider-discovered` for MCP tools/resources/prompts discovered from `tools/list`, `resources/list`, or `prompts/list`. Avoid `dynamic tools` / `dynamic registry` in new MCP design prose because those phrases imply that model-visible tool schemas may change during an active LLM run.

The intended invariant is:

```text
provider-discovered at startup / provider initialization;
registered into the ordinary ToolRegistry before model exposure;
run-stable for the duration of a model request/run;
refreshed only at a safe boundary or reported as a diagnostic.
```

## Later follow-ups

- Richer MCP task/task-support integration if ordinary tool-call fallback is insufficient.
- Streamable HTTP transport.
- OAuth / remote auth.
- Registry/package distribution.
- Explicit MCP/Plugin bridge only if separately approved; do not conflate Plugin packages with MCP local server execution.

## Success criteria

- A local mock MCP server can be configured explicitly and initialized.
- Discovered MCP tools appear as ordinary Yoi tools with stable namespacing.
- Tool calls go through ordinary permission and history paths.
- MCP resources/prompts are explicit operations, not hidden context injections.
- MCP result forms are bounded and safely serialized.
- Secret values, command/env details, and server diagnostics are redacted where required.
- Local server trust boundary is documented: Yoi does not sandbox the configured executable through feature authority.
- Feature, Plugin, and MCP permission/trust responsibilities are documented as separate layers.
