[v1.x] docs: point the README at v2 and say what v1.x supports

[claude]

Requested by Felix Weinberger · Slack thread

Before: the README did not say that v1.x is the maintenance line or point readers at v2.

After: a banner under the title says v1.x implements the spec up to 2025-11-25, that the 2026-07-28 spec is in v2 (packages, docs and migration guide linked), and how long v1.x gets fixes; the licence badge links to this branch's LICENSE and the spec link names 2025-11-25.

README only, no changeset.

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https://claude.ai/code/session_012VRbFCp41otcScXE1YY3es

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Latest commit: 107e66d

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commit: 107e66d

[claude]

I reviewed this PR and didn't find any bugs. Since the banner makes several claims about v2 that can't be checked from this repo, a maintainer's confirmation of those facts would still be worthwhile.

What was reviewed:

• The "spec up to 2025-11-25" claim matches LATEST_PROTOCOL_VERSION in src/types.ts; the Overview link now points at the dated spec instead of draft, which is more accurate for a maintenance line even though src/spec.types.ts is generated from the draft schema.
• The LICENSE badge now links to blob/v1.x/LICENSE, which is the right branch for this README; the file exists on the branch.
• Not verifiable from the checkout: the v2 release date (2026-07-27), the six-month support window, the @ modelcontextprotocol/server / client package names, and the ts.sdk.modelcontextprotocol.io v2 and migration URLs. ROADMAP.md on this branch still describes v2 as "planned ... around mid-2026", so it may be worth a follow-up to keep the two documents consistent.

Extended reasoning...

The change is README.md only: a v1.x maintenance banner, a badge branch switch from main to v1.x, and the Overview spec link changed from draft to 2025-11-25. It touches no code and no security-sensitive surface. The in-repo facts are consistent (LATEST_PROTOCOL_VERSION is 2025-11-25, package.json is 1.32.0, CLAUDE.md describes the branch as the maintenance line). Deferring rather than approving because .github/CODEOWNERS assigns every path to the typescript-sdk team, and the banner's external claims (v2 release date, support window, package names, doc URLs) cannot be verified from the checkout and only a maintainer can confirm them.