[Bug] MCP HTTP Transport: JSON-RPC validation paradox - rejects valid jsonrpc: 2.0

Bug Report: Claude Code MCP HTTP Transport - JSON-RPC Validation Error

Summary

Z.ai MCP servers (HTTP type) fail to connect during startup due to a JSON-RPC schema validation bug in Claude Code's MCP client. The server sends valid {"jsonrpc": "2.0"} but the client's schema validator rejects it.

Environment

• Claude Code: 2.1.12 (native)
• Node: v24.3.0
• Platform: Linux (Fedora)

Affected MCPs

• web-search-prime (https://api.z.ai/api/mcp/web_search_prime/mcp)
• zread (https://api.z.ai/api/mcp/zread/mcp)
• web-reader (https://api.z.ai/api/mcp/web_reader/mcp)

Error from Debug Log

\\\
[DEBUG] MCP server "web-search-prime": HTTP Connection failed after 1176ms: [
{
"code": "invalid_union",
"errors": [
{
"code": "invalid_value",
"values": ["2.0"],
"path": ["jsonrpc"],
"message": "Invalid input: expected \"2.0\""
}
]
}
]
\\\

Root Cause

The MCP server sends valid {"jsonrpc": "2.0"} but Claude Code's schema validator rejects it, creating a paradox where the expected value ("2.0") is received but marked as invalid.

Evidence That Auth/Env Vars Work

• "hasAuthProvider": true in debug logs
• "Authorization":"[REDACTED]" (key was resolved from env var)
• Tools worked during active session (webReader successfully fetched pages)
• Only fails during startup MCP handshake

Steps to Reproduce

1. Configure any HTTP MCP with Z.ai services
2. Use environment variable in Authorization header (e.g., "Authorization": "Bearer ZAI_GLM_CODING_PLAN_API_KEY")
3. Restart Claude Code
4. Check MCP status with \claude mcp list\

Expected Behavior

MCP servers should connect successfully.

Actual Behavior

Connection fails with JSON-RPC validation error during startup.

Additional Context

The same MCP tools work when called during an active session, suggesting the validation bug only affects the startup handshake process.