:bug: SSE response bodies starting with id: field bypass parsing and fail with JSON error

[evaline-ju]

Describe the bug

When the MCP Gateway sends SSE-formatted tool responses where the stream begins with an id: line (a standard SSE field), the ext-proc fails to detect it as SSE and falls through to the plain JSON parser, which errors on the raw SSE text

Steps To Reproduce

Leverage the everything MCP server echo tool and elicit/provide a tool response that should be blocked

Expected Behavior

Tool response should be blocked by the rail if the tool response contains the unexpected content checked by the rail

Additional Context

No response