MCP's skills extension SEP-2640 is Accepted, and the conformance suite now grades clients by what they refuse to fetch

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modelcontextprotocol/conformance merged PR #330 on 2026-09-11, adding a requirement-traceability file for SEP-2640 after the SEP passed the core-maintainer vote on 2026-09-01. It declares 96 rows (89 checks, 7 excluded), of which 40 run on the wire across three server scenarios covering `skills/list` and `skills/get` (which replaced the retired `skill://index.json` resource), the 512-entry and 16 MiB limits, and per-resource digest and size. Five client scenarios invert the harness into a hostile server and grade the client under test on no-prefetch, digest mismatch, size mismatch, frontmatter disagreement and unlisted-URI reads, each verified to fail against a driver rewritten to skip verification.