hermes - 💡(How to fix) Fix [Bug]: MCP over HTTP (SSE) Transport failing to maintain session ID [1 comments, 2 participants]

1. Configure an MCP server in ~/.hermes/config.yaml using an HTTP URL (e.g., url: http://127.0.0.1:8000/mcp).
2. Ensure the MCP server is running and expects text/event-stream (SSE).
3. Attempt to use a tool that is provided by that MCP server.

Technical Evidence
Diagnostic httpx test results:
json
{
  "jsonrpc": "2.0",
  "id": "server-error",
  "error": {
    "code": -32600,
    "message": "Bad Request: Missing session ID"
  }
}

lsof confirms that other agents (e.g., claude CLI) are successfully maintaining established connections to the same endpoint, confirming the server implementation is correct and the issue resides in the hermes-agent gateway's transport logic.

The hermes-agent gateway should:
1. Initiate an SSE connection to the endpoint.
2. Capture the mcp-session-id from the server's response headers.
3. Include this mcp-session-id in subsequent JSON-RPC requests to maintain the session.

The gateway fails to manage the session ID correctly. Based on diagnostic testing:
- A standard GET request without the correct Accept header returns 406 Not Acceptable.
- An SSE-ready request (using text/event-stream) returns 400 Bad Request with the error: {"jsonrpc":"2.0","id":"server-error","error":{"code":-32600,"message":"Bad Request: Missing session ID"}}.

This indicates that while the connection is being attempted, the mcp-session-id provided by the server during the handshake is not being correctly propagated by the gateway in subsequent calls.

--- hermes dump ---
version:          0.12.0 (2026.4.30) [6bc5d722]
os:               Linux 6.8.0-100-generic x86_64
python:           3.11.15
openai_sdk:       2.32.0
profile:          default
hermes_home:      ~/.hermes
model:            gemma-4-26b-a4b-it
provider:         gemini
terminal:         local

api_keys:
  openrouter           set
  openai               not set
  anthropic            not set
  anthropic_token      not set
  nous                 not set
  google/gemini        set
  gemini               not set
  glm/zai              not set
  zai                  not set
  kimi                 not set
  minimax              not set
  deepseek             not set
  dashscope            not set
  huggingface          not set
  nvidia               not set
  ai_gateway           not set
  opencode_zen         not set
  opencode_go          not set
  kilocode             not set
  firecrawl            not set
  tavily               not set
  browserbase          not set
  fal                  not set
  elevenlabs           not set
  github               not set

features:
  toolsets:           hermes-cli
  mcp_servers:        1
  memory_provider:    built-in
  gateway:            stopped (systemd (user))
  platforms:          none
  cron_jobs:          2 active / 2 total
  skills:             108

config_overrides:
  agent.max_turns: 60
  display.streaming: True
--- end dump ---


--- agent.log (last 200 lines) ---
(file empty)

--- errors.log (last 100 lines) ---
(file empty)

--- gateway.log (last 100 lines) ---
(file not found)




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O comando hermes debug share --local não exibe essas falhas de comunicação de ferramentas, pois elas são tratadas como falhas de execução de função (tool calls) e não como crashes do processo hermes-agent.