feat(python): qualify frozen MCP requirements

[jeremydixon22]

Summary

• complete the Python host's test-only MCP 2026-07-28 diagnostic surface for tools, content blocks, prompts, resources, completion, MRTR, progress, and JSON Schema 2020-12
• replace the 16-scenario preview with the pinned official runner's complete frozen requirements profile
• retain runner evidence in Python qualification and release artifacts, and reject publication-policy regressions to a partial gate
• restrict conformance diagnostics to loopback binds and keep ordinary product catalogs unchanged

Verification

• Relevant unit and conformance tests pass.
• Public API, contract, and maturity documentation is updated when applicable.
• Provider-specific behavior has an opt-in live gate and does not widen a portable claim.
• No credentials, customer data, local paths, generated artifacts, or deployment identities are included.
• Release artifacts and public export were rehearsed when a package, client, container, or workflow changed.

Local evidence:

• Python runtime: 205 tests, 78.8% branch-aware coverage, strict mypy, wheel/sdist and clean-install gates
• official MCP runner 0.2.0-alpha.11: 50 scenarios, 189 passed, 0 failed under --requirements 2026-07-28
• deterministic public export: 817 files, tree a17bb96f9872e016aaa2b515b5a50ff924c43fd64309de5c0ae63c9bb52dcd12

Compatibility and operations

No product catalog or default network surface is widened. Conformance fixtures remain disabled by default and the packaged CLI refuses to expose them from a non-loopback bind. The Python MCP qualification becomes broader and retains more evidence, so its hosted run may take slightly longer.