fix(server): application/json header for notifictions

[mattzcarey]

closes #1356

Motivation and Context

How Has This Been Tested?

Breaking Changes

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

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🦋 Changeset detected

Latest commit: 17d8fd3

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

This PR includes changesets to release 1 package

Name	Type
@modelcontextprotocol/server	Patch

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commit: 17d8fd3

[DePasqualeOrg]

@mattzcarey, I'm curious about the reasoning for this, since I'm referring to the TypeScript SDK in my development of this Swift SDK. Since notification responses have an empty body, specifying a content type seems unnecessary, and it isn't mentioned in the spec. The TypeScript SDK also doesn't include a content type for DELETE 200 responses. Are there clients that expect this in practice?

[mattzcarey]

@mattzcarey, I'm curious about the reasoning for this, since I'm referring to the TypeScript SDK in my development of this Swift SDK. Since notification responses have an empty body, specifying a content type seems unnecessary, and it isn't mentioned in the spec. The TypeScript SDK also doesn't include a content type for DELETE 200 responses. Are there clients that expect this in practice?

Hey this closed an issue which was effecting people using the Java client. Please see the issue this closed

[mattzcarey]

Happy to revisit this if you think it was misplaced.

[DePasqualeOrg]

It looks like the Java client now handles the previous (correct) behavior of the TypeScript HTTP server correctly and will log a warning about a non-compliant response with the new behavior from this PR.

So unless I'm misunderstanding something, this should probably be reverted.