envoyproxy/envoy

Feature Request: Support for MCP 241105 Spec in Envelope Stateful Session Extension

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#40,247 opened on Jul 16, 2025

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Description

Title: Support MCP 241105 Spec in Envelope Stateful Session Extension

Description:

The current envelope stateful session extension (introduced in PR #39004) only supports the MCP 250326 spec (header-based session tracking).

However, the MCP 241105 spec is not supported. This spec requires Envoy to decode the initial SSE event in the upstream response, extract and update the session ID, and manage the session context accordingly.

Supporting MCP 241105 would enable compatibility with upstream servers and clients that rely on this protocol for session management, especially for SSE-based applications.

Please consider adding native support for MCP 241105 in the envelope stateful session extension, so that Envoy can handle session context as required by this spec, without relying on Lua scripts or external workarounds.

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Contributor guide

Research direction
Inspect the existing envelope stateful session extension (PR #39004) and understand how it handles session IDs via headers. Then study the MCP 241105 spec to learn how session IDs are extracted from the first SSE event in the upstream response. Implement decoding of the initial SSE event to update session context accordingly.
Tech stack
cpp
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
C++Envoy extension developmentMCP protocol
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50