MCP server type 'remote' fails with 405 against local MCP endpoints requiring POST transport

Bug: MCP local server (type: remote) fails with 405 against Supabase local MCP endpoint

Description

When configuring an MCP server with type: "remote" pointing to a local Supabase MCP endpoint (Supabase CLI MCP), OpenCode gets Non-200 status code (405) and reports "SSE error".

Root Cause

The Supabase CLI MCP endpoint does NOT support SSE (GET). It only accepts POST JSON-RPC after the MCP handshake. OpenCode with type: "remote" sends an SSE-style GET request, which the endpoint rejects with 405.

Config (from official Supabase Studio instructions)

{
  "mcp": {
    "supabase-local": {
      "type": "remote",
      "url": "http://127.0.0.1:54321/mcp?features=docs%2Cdatabase%2Cdebugging%2Cdevelopment",
      "enabled": true
    }
  }
}

Evidence

1. supabase status confirms MCP is running on the endpoint
2. OpenCode panel shows: supabase-local SSE error: Non-200 status code (405)
3. Direct curl POST works with JSON-RPC
4. psql direct connection works (schema and database fully functional)

Expected Behavior

OpenCode should use POST-based MCP transport for type: "remote" servers that don't support SSE, or negotiate the transport protocol during handshake.

Workaround

Use psql directly on port 54322 with the local Postgres instance.

Environment

• OpenCode version: latest
• OS: Linux
• Supabase CLI: local dev MCP server
• The endpoint serves MCP over POST, not SSE