v0.15.0

Author-side MCP server — roadmap §5.3 (the agent keystone).

Added

• redstart mcp — a Model Context Protocol server. Exposes the toolchain the
  compiler already owns as MCP tools an AI agent can drive in a write → check → fix
  loop, over stdio (newline-delimited JSON-RPC 2.0, no external SDK):

  • check — type-check a project (path) or inline source and return the
    same structured diagnostics as redstart check --json (errors and lint
    warnings, each with a code, message, and file/line). A parse/load failure is
    returned as a normal { ok: false, diagnostics } result, not a tool error, so
    the agent always gets machine-readable feedback. This is the keystone tool.
  • explain — explain a diagnostic code (what triggers it, the footgun it
    prevents, the fix); omit code to list every code.
  • build — emit schema.graphql, subgraph.yaml, and src/mappings.ts,
    returning the artifacts (and optimisation notes); write: true also writes them.
  • test — run the project's test blocks natively and return per-test results.

  New redstart-mcp crate; the CLI gains the redstart mcp subcommand alongside
  redstart lsp.