fix: allow MIME type parameters in resource validation (RFC 2045)

[antonpk1]

Summary

• Updates MIME type validation regex to support RFC 2045 parameters
• Fixes issue where valid MIME types like text/html;profile=mcp-app were rejected
• Adds comprehensive tests for parameterized MIME types

Fixes #1754

Details

The MIME type validation regex in FastMCP's Resource class was too restrictive:

# Before (rejects parameters)
pattern=r"^[a-zA-Z0-9]+/[a-zA-Z0-9\-+.]+$"

# After (supports parameters)
pattern=r"^[a-zA-Z0-9]+/[a-zA-Z0-9\-+.]+(;\s*[a-zA-Z0-9\-_.]+=[a-zA-Z0-9\-_.]+)*$"

Now supports:

• Basic types: text/plain, application/json
• With parameters: text/html;profile=mcp-app, application/json; charset=utf-8
• Multiple parameters: text/plain; charset=utf-8; format=fixed

Test plan

• New test file tests/issues/test_1754_mime_type_parameters.py with 4 test cases
• All existing resource tests pass (312 FastMCP tests)
• Linting and formatting pass

🤖 Generated with Claude Code

[maxisbey]

Thanks for fixing this! The regex change correctly handles the common parameter cases needed for MCP Apps SDK compatibility.

One note: the regex is still more restrictive than RFC 2045 (doesn't support quoted string values like charset="utf-8"), but this covers the practical use cases. Opened #1756 to track aligning with the TypeScript SDK approach.

[github-actions]

This PR is included in version v1.23.3