[BUG] AWS MCP proxy (mcp-proxy-for-aws) fails during initialization with -32602: Invalid request parameters

Bug Description

AWS MCP servers (using mcp-proxy-for-aws) show "Connected" status in claude mcp list but fail to load any tools. The connection establishes successfully and reports capabilities, but subsequent tool/resource fetch requests fail with error -32602: Invalid request parameters.

Environment

• Claude Code version: 2.1.29
• mcp-proxy-for-aws version: Client v1.1.6, Server v2.14.0
• OS: macOS (Darwin 24.6.0)
• Node version: v22.13.1

MCP Configuration

{
  "mcpServers": {
    "aws-mcp-prd": {
      "command": "uvx",
      "args": [
        "mcp-proxy-for-aws",
        "--sse-url",
        "https://mcp.prd.bedrockchat.aws.anthropic.com/sse"
      ],
      "env": {
        "AWS_PROFILE": "tpg-prd"
      }
    }
  }
}

Steps to Reproduce

1. Configure AWS SSO profile and verify credentials work:

``bash
aws sso login --profile tpg-prd
aws sts get-caller-identity --profile tpg-prd # Should return valid identity
``

1. Add AWS MCP server to Claude Code config (as shown above)

1. Start Claude Code and check MCP status:

``bash
claude mcp list
``

1. Observe: Server shows "Connected" but no tools are loaded

1. Check debug logs:

``bash
grep "aws-mcp" ~/.claude/debug/latest
``

Expected Behavior

AWS MCP server should connect and load tools successfully, similar to other MCP servers (github, grafana, etc.).

Actual Behavior

Connection establishes with capabilities detected, but tool loading fails:

2026-01-30T16:54:14.891Z [DEBUG] MCP server "aws-mcp-main": Connection failed after 2460ms: MCP error -32602: Invalid request parameters
2026-01-30T16:54:14.891Z [ERROR] MCP server "aws-mcp-main" Connection failed: MCP error -32602: Invalid request parameters

Additional Context

• Other MCP servers (github, grafana, notion, linear) using stdio transport work correctly
• AWS SSO credentials are valid and work with AWS CLI
• The proxy starts without errors when run standalone
• Issue occurs in both fresh conversations and resumed ones
• claude mcp list shows "Connected" status despite the failure

Diagnostic Information

| Component | Status |
|-----------|--------|
| AWS SSO credentials | ✓ Valid |
| MCP connection status | ✓ Shows "Connected" |
| Capabilities detected | ✓ {"hasTools":true,"hasPrompts":true,"hasResources":true} |
| Tools loaded | ✗ None |

Related Issues

• #9608 - Similar MCP session handling issue but with different error (-32001: Session not found)
• #18296 - HTTP transport issues (different root cause)

Hypothesis

The error -32602: Invalid request parameters suggests a protocol mismatch between Claude Code and the mcp-proxy-for-aws during the tools/list or resources/list request phase. This could be:

1. A parameter format difference expected by the proxy
2. A protocol version incompatibility
3. A regression in recent proxy versions