MCP get_products fails even with brand_manifest (while A2A works)

[bokelley]

Summary

When testing agents (including the public Test Agent and Wonderstruck) via MCP protocol, get_products calls fail even when a valid brand_manifest is provided. The same calls work correctly via A2A protocol.

Reproduction

Agent URLs tested:

• https://test-agent.adcontextprotocol.org
• https://wonderstruck.sales-agent.scope3.com

Results from JavaScript client tests:

Agent	MCP Status	A2A Status
Test Agent	✅ Working	✅ Working
Wonderstruck	⚠️ Partial (get_products fails)	✅ Working

Test parameters used:

{
  "brief": "Show me all available advertising products across all channels",
  "brand_manifest": {
    "name": "E2E Test Brand",
    "url": "https://test.example.com"
  }
}

Expected Behavior

Both MCP and A2A protocols should return products when a valid request is provided.

Actual Behavior

• A2A: Returns 5 products ✅
• MCP: Fails to return products ❌

Environment

• @adcp/client testing module
• Protocol: MCP (JSON-RPC over HTTP)
• AdCP version: 2.5.x

Questions

1. Is there a difference in how MCP vs A2A requests are processed?
2. Is there additional validation or middleware in the MCP path that might be rejecting valid requests?
3. Is the MCP endpoint properly exposing get_products as a tool?

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