Add ChatGPT App SDK output format support

[rvguha]

Summary

Implement ChatGPT App specification v0.5 output format to enable rich UI widgets in ChatGPT Apps. This allows NLWeb to display search results using ChatGPT's native list widgets.

Backend Changes

Core Files Modified

• core/baseHandler.py: Add output_format parameter (default: "default")
• core/schemas.py: Add format_response_to_chatgpt_spec() utility function
• core/utils/message_senders.py: Transform responses and filter messages for chatgptapp format
• webserver/mcp_wrapper.py: Add output_format to MCP ask tool (defaults to "chatgptapp")

Response Format

When output_format=chatgptapp:

SSE Stream:

data: {"_meta": {"conversation_id": "", "version": "0.5", "openai/outputTemplate": "ui://widget/list.html", "query_rewrite": {...}, "decontextualized_query": "..."}}
data: {"content": [{"type": "resource", "resource": {"data": [{"@type": "Item", ...}]}}]}
data: {"content": [{"type": "resource", "resource": {"data": [...]}}]}

Filtered Messages:

• Skip: begin-nlweb-response, end-nlweb-response, query_rewrite, decontextualized_query, and all other non-result messages
• Only _meta (sent once) and content blocks are included

Frontend Changes

• static/index.html: Set SSE as default connection type (was WebSocket)
• Users can still use WebSocket with ?mode=websocket

Key Features

• ✅ Full backward compatibility - default format unchanged
• ✅ Preserves all data fields from original format
• ✅ Enables ChatGPT Apps SDK generic list widget
• ✅ Works with any schema.org type (Restaurant, Recipe, Article, Product, etc.)
• ✅ Clean output with only _meta and content blocks
• ✅ MCP defaults to chatgptapp format

Usage

HTTP/SSE:

/ask?query=pizza&site=seriouseats&output_format=chatgptapp

MCP:

{
  "name": "ask",
  "arguments": {
    "query": "pizza",
    "site": ["seriouseats"],
    "output_format": "chatgptapp"
  }
}

Test Plan

• Tested with production endpoint
• Verified all fields preserved
• Confirmed only _meta and content messages sent
• Validated ChatGPT App spec v0.5 compliance
• Tested MCP integration