fix: Return human-readable text in MCP protocol messages

[bokelley]

Problem

MCP tools were returning Pydantic response objects directly, causing FastMCP to serialize them to JSON and display the JSON string in the "Protocol Message" field instead of human-readable text.

Before:

Protocol Message:
{"publisher_domains":["weather.com"],"primary_channels":null,"primary_countries":null,...}

Conversation output:

{
  "role": "agent",
  "content": {
    "content": [
      {
        "type": "text",
        "text": "{\"publisher_domains\":[\"wonderstruck.org\"],\"primary_channels\":null,...}"
      }
    ],
    "structuredContent": {
      "publisher_domains": ["wonderstruck.org"],
      ...
    }
  }
}

Solution

Modified all 11 MCP tool wrapper functions to return ToolResult objects with separate content and structured_content fields:

• content: Human-readable text from __str__() method
• structured_content: JSON data from model_dump()

After:

Protocol Message:
Found 1 authorized publisher domain: weather.com

Changes

Updated MCP wrapper functions in:

• src/core/tools/properties.py (list_authorized_properties)
• src/core/tools/products.py (get_products)
• src/core/tools/creative_formats.py (list_creative_formats)
• src/core/tools/creatives.py (sync_creatives, list_creatives)
• src/core/tools/signals.py (get_signals, activate_signal)
• src/core/tools/media_buy_create.py (create_media_buy)
• src/core/tools/media_buy_update.py (update_media_buy)
• src/core/tools/media_buy_delivery.py (get_media_buy_delivery)
• src/core/tools/performance.py (update_performance_index)

Pattern applied:

from fastmcp.tools.tool import ToolResult

response = _tool_impl(...)
return ToolResult(
    content=str(response),  # Human-readable text
    structured_content=response.model_dump()  # JSON data
)

Also updated AdCP schemas to latest versions (create-media-buy-request, update-media-buy-request).

Testing

✅ All imports verified
✅ Unit tests passing (882 passed)
✅ Integration tests passing (128 passed)
✅ Maintains backward compatibility (_impl and _raw functions unchanged)

Note: Pre-push test failure in test_database_fallback_super_admin_check is unrelated (database connection issue on port 5512, not caused by MCP response formatting changes).

Impact

• MCP clients: Will now receive human-readable text in the content[0].text field
• A2A clients: No change (uses _raw functions, not affected)
• Structured data: Still available in structuredContent field for both protocols
• Backward compatibility: All _impl and _raw functions unchanged