fix: update the draft wire version to 2026-07-28

[felixweinberger]

Aligns the harness's draft wire protocolVersion with what the spec's draft
schema actually declares: 2026-07-28 instead of the old DRAFT-2026-v1
placeholder.

Motivation and Context

The spec repo pinned the draft protocol version to the RC date in
modelcontextprotocol/modelcontextprotocol#2791: schema/draft/schema.ts now
declares LATEST_PROTOCOL_VERSION = "2026-07-28". The harness's
DRAFT_PROTOCOL_VERSION (src/types.ts) is documented as mirroring that
constant ("bump when that constant changes"), but still carried the
placeholder. As a result, an SDK that implements the draft spec and sends the
version the draft schema declares cannot pass the draft suite — the mock
server refuses to negotiate it, and scenario checks that assert the version
string fail. #315 already anticipated swapping the placeholder for "the real
value when available"; this PR does that swap.

Two commits:

1. chore: sync spec-types to modelcontextprotocol@0168c57f — refreshes the
   vendored schemas via npm run sync-schema (only draft.ts and SOURCE
   change; the dated schemas are identical).
2. fix: update the draft wire version to 2026-07-28 — bumps
   DRAFT_PROTOCOL_VERSION, updates the hard-coded literals in tests, the
   example servers, and the README, and adds src/types.test.ts pinning
   DRAFT_PROTOCOL_VERSION to the vendored draft schema's
   LATEST_PROTOCOL_VERSION so the two can no longer drift silently (plus a
   guard that the draft identifier stays distinct from the dated versions).

How Has This Been Tested?

• npm test: 270 passed (270), 26 test files — includes the new
  src/types.test.ts invariant tests
• npm run check (tsgo typecheck + eslint + prettier): clean
• npm run build: clean

Breaking Changes

For anyone already running the draft suite against DRAFT-2026-v1: the
accepted wire version is now 2026-07-28, and --spec-version DRAFT-2026-v1
no longer resolves. The draft alias is unaffected and remains the
recommended way to target the draft suite. Dated-version behavior
(2025-03-26 / 2025-06-18 / 2025-11-25) is unchanged.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

2026-07-28 looks like a dated release identifier but is still the draft: it
is the RC date the spec pinned in advance (see
modelcontextprotocol/modelcontextprotocol#2791). The harness keeps treating it
as the draft version — distinct from DATED_SPEC_VERSIONS, selected by the
draft alias and suite — so nothing about scenario applicability or version
ordering changes, only the wire string.

[pkg-pr-new]

Open in StackBlitz

npx https://pkg.pr.new/@modelcontextprotocol/conformance@331

commit: b42db5f