Support (configurable) user approval/denial of MCP tool-use requests

A new checkbox on the setup page controls whether to require approval of MCP tool calls:

If approval is enabled, we handle MCP tool call requests by rendering a user approve/deny widget:

A new route handles submitting the approval/denial and resuming the conversation.

MCP server support

Template now supports connecting to remote MCP servers!

• Enable MCP tools on the setup page to set a config variable in .env
• Provide MCP server connection details on the setup page to populate tool.config.json
• MCP tool calls are auto-approved by default; support for tool call approval is planned for a future version

The tool.config.json file stores MCP and custom function settings. This file:

• is git-ignored by default because it may contain authentication secrets
• is auto-created with default values by an app lifecycle handler if it doesn't exist

The Responses API does not include MCP tool outputs in the event stream, so (unlike with custom functions) you will not be able to display them in the chat UI.

Register custom functions and tool output templates from the setup page

A major enhancement to custom function support: you can now register custom functions (and optionally HTML templates for displaying function results to the user) directly on the /setup page!

After registration,

1. A tool definition will be auto-generated from your function and provided to the assistant,
2. The assistant's JSON tool calls will be automatically dispatched to the correct function, and
3. Outputs will be automatically rendered in your template, if you provided one.