[Epic] MCP server & OpenAPI schema generation

Harper's MCP server and the schema generation it shares with OpenAPI. This epic gives that work a live parent.

## Why this exists

#1349 (`MCP server: complete the protocol surface`) was the de facto MCP epic, and it is **closed as completed** while still holding three open children — #1107, #1368, and #1548. Open work under a closed parent doesn't show up in any epic-progress view, so those are adopted here along with the MCP issues that were never parented at all.

## Scope

**In:** the MCP protocol surface (sessions, subscriptions, streaming, protocol-era handling), tool and resource registration, and the schema type mapping shared between MCP and OpenAPI.

**Out:** the operations API itself (#1681) — MCP exposes it, but defects in the operations are that epic's. General component-authoring concerns (#1678) unless MCP-specific.

_Created during backlog triage; the child issues keep their own priorities and milestones._

This is a parent epic rather than a self-contained task. Start by reading the adopted child issues #1107, #1368, and #1548, along with the unparented MCP issues, and use the stated in-scope protocol and schema areas to identify a concrete task. Done means the relevant child work is completed without expanding into the excluded operations API or general component authoring.

Written by the indexing model from the issue text.