fix(server): allow streamable HTTP JSON without content type

[pragnyanramtha]

Summary

• remove the Streamable HTTP request Content-Type requirement from the web-standard server transport
• keep invalid body handling in the existing req.json() parse-error path
• add server and Node wrapper regression coverage for valid JSON POSTs without Content-Type

Fixes #581.

Testing

• pnpm --filter @modelcontextprotocol/server test -- streamableHttp.test.ts
• pnpm --filter @modelcontextprotocol/node test -- streamableHttp.test.ts
• pnpm --filter @modelcontextprotocol/test-integration test -- test/server/cloudflareWorkers.test.ts (locally runs the full integration project: 16 files / 423 tests)
• nvm exec 20.20.2 pnpm --filter @modelcontextprotocol/test-integration test -- test/server/cloudflareWorkers.test.ts (same full integration project under Node 20.20.2)
• pnpm --filter @modelcontextprotocol/server typecheck
• pnpm --filter @modelcontextprotocol/server lint
• pnpm --filter @modelcontextprotocol/node typecheck
• pnpm --filter @modelcontextprotocol/node lint
• NODE_OPTIONS=--max-old-space-size=4096 pnpm --filter @modelcontextprotocol/server build
• NODE_OPTIONS=--max-old-space-size=4096 pnpm --filter @modelcontextprotocol/node build
• git diff --check

Notes

• Independent review found no blocking issues. It called out that accepting valid JSON with Content-Type: text/plain is consistent with the issue's proposed full guard removal and the Streamable HTTP spec's lack of a request Content-Type requirement.
• The repo pre-push hook was attempted. Full workspace typecheck completed, but the hook did not finish because @modelcontextprotocol/test-helpers lint currently fails on untouched vitest dependency classification, and the workspace @modelcontextprotocol/node build hit Node's default heap limit. The targeted node/server builds pass with NODE_OPTIONS=--max-old-space-size=4096.

[changeset-bot]

🦋 Changeset detected

Latest commit: a065091

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@modelcontextprotocol/server	Patch
@modelcontextprotocol/express	Patch
@modelcontextprotocol/fastify	Patch
@modelcontextprotocol/hono	Patch
@modelcontextprotocol/node	Patch

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commit: a065091

[Copilot]

Pull request overview

Removes the strict Content-Type: application/json requirement from the web-standard Streamable HTTP server transport, aligning with the MCP spec which doesn't mandate a request Content-Type. Invalid JSON bodies are still caught by the existing req.json() parse-error path.

Changes:

• Drop the 415 Unsupported Media Type guard in WebStandardStreamableHTTPServerTransport.
• Update server tests to accept valid JSON with missing or non-JSON Content-Type, and assert invalid bodies now return 400 Parse error.
• Add a changeset documenting the patch.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/server/src/server/streamableHttp.ts	Removes the Content-Type validation block that returned 415.
packages/server/test/server/streamableHttp.test.ts	Replaces 415-rejection tests with acceptance tests for missing/non-JSON Content-Type.
packages/middleware/node/test/streamableHttp.test.ts	Adds Node wrapper test for missing Content-Type; updates plain-text body test to expect 400 parse error.
.changeset/fix-streamable-http-content-type.md	Patch changeset entry for the server package.

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