Add streamable HTTP readiness suite for MCP interoperability

[dgenio]

Context / Problem

• Transport evolution can cause hidden compatibility regressions.
• Current checks focus on core paths, not full streamable HTTP behavior.
• Teams need release confidence for protocol interoperability.

Proposal

• Add readiness suite for MCP streamable HTTP behavior.
• Cover session headers, reconnect flow, and version headers.
• Cover POST and SSE response handling paths.
• Report pass or fail matrix by capability group.

Acceptance Criteria

• Suite validates negotiated protocol-version behavior.
• Suite validates session ID lifecycle handling.
• Suite validates reconnect and resume expectations.
• CI runs suite in non-gating mode first.

Implementation Notes

• Keep fixtures versioned by MCP spec date.
• Separate transport conformance from business logic tests.
• Document known unsupported behaviors.

Tasks / Checklist

• Define conformance matrix and fixtures.
• Implement transport test harness.
• Add regression tests for known edge cases.
• Document migration and compatibility notes.

References

• MCP specification latest: https://modelcontextprotocol.io/specification/latest
• MCP transport details: https://modelcontextprotocol.io/specification/2025-06-18/basic/transports