yoi/.yoi/objectives/00001KTR80WMN/item.md

title	state	created_at	updated_at
MCP local stdio integration architecture	active	2026-06-10T07:48:45Z	2026-06-13T15:30:22Z

Objective

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

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

Strategic direction

• Baseline the 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 be hidden context injection.
  • They must be explicit tool operations with history records.
• Use the normal Yoi tool registry, 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, dynamic 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 dynamic tools/resources/prompts are exposed through the feature API and ordinary Yoi tool paths.

Work breakdown

1. 00001KTR81P9X — Extend pod::feature API for protocol-backed external providers.
   • provider/service lifecycle
   • startup discovery and dynamic contribution registration
   • bounded refresh semantics
   • metadata/result normalization
   • no feature-layer authority model for MCP/Plugin permissions
2. 00001KTR82RB7 — Implement MCP 2025-11-25 local stdio server bridge.
   • explicit MCP config and trust model
   • initialize/capability negotiation
   • tools/resources/prompts list/call/read/get
   • bounded result serialization
   • list-changed diagnostics/refresh behavior
3. 00001KV0SP0TY — Remove feature-layer HostAuthority model.
   • remove authority/grant terminology from pod::feature
   • keep real permission/trust policy in owning Plugin/MCP/manifest/tool layers
4. Later follow-ups, if needed.
   • richer MCP tasks / task-support integration
   • remote/HTTP transports
   • OAuth / registry / package distribution
   • Plugin package/runtime alignment, if an explicit MCP/plugin bridge is later approved

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.