fix: handle MCP SSE text/event-stream 400 error

[bitxeno]

Problem

MCP servers using modelcontextprotocol/go-sdk Streamable HTTP transport return HTTP 400 when the initial GET request doesn't include proper Accept headers:

resolving source "http://xxx.com/mcp": fetching "http://xxx.com/mcp": unexpected HTTP status 400

Error source: https://github.com/modelcontextprotocol/go-sdk/blob/ea161959d7c87bd3d4bbd63cfa8df01d3ab3b304/mcp/streamable.go#L292

The server returns:

• Status: 400 Bad Request
• Body: Accept must contain 'text/event-stream' for GET requests

Solution

Add detection for text/event-stream in the 400 response body to trigger direct MCP URL resolution, consistent with existing handling for 401/403/405 status codes.

Changes

• internal/bootstrap/resolve.go - Check for text/event-stream in 400 error body
• internal/bootstrap/resolve_helpers_test.go - Add test case for the new behavior

[lydakis]

Thanks, this looks like a real compatibility issue. Could you also add an end-to-end regression test in internal/bootstrap/resolve_test.go that covers this 400 Bad Request text/event-stream response path through Resolve(...)?

[bitxeno]

Thanks, this looks like a real compatibility issue. Could you also add an end-to-end regression test in internal/bootstrap/resolve_test.go that covers this 400 Bad Request text/event-stream response path through Resolve(...)?

Added

[lydakis]

Looks good, thanks for contributing, really appreciate it!