Add MCP resource support to MCPClient

[bnovik0v]

Summary

The MCP specification defines resources as read-only data exposed by MCP servers (files, database records, application state, real-time signals, etc.). Currently, MCPClient only supports tools — there is no way to list or read resources from an MCP server.

Motivation

Resources are a core MCP primitive alongside tools and prompts. Common use cases for voice/multimodal agents:

• Device state — current song playing, application open, sensor readings
• User context — profile data, preferences, session history
• Knowledge bases — documents, FAQs, product catalogs injected into the system prompt
• Real-time signals — IoT data, monitoring dashboards, live metrics

Without resource support, users who need this functionality have to bypass MCPClient entirely and use the raw mcp SDK to manage their own sessions — losing the benefits of Pipecat's persistent session management.

Proposed API

Add three methods to MCPClient, following the same patterns as the existing tool methods:

async with MCPClient(server_params=...) as mcp:
    # List available resources (metadata only)
    resource_list = await mcp.list_resources()
    # resource_list.resources -> List[MCPResource]
    # resource_list.supports_subscribe -> bool
    # resource_list.supports_list_changed -> bool

    # Read a specific resource
    resource = await mcp.read_resource("file:///config.json")
    # resource.text or resource.blob

    # Convenience: list + read all
    all_resources = await mcp.read_all_resources()

New dataclasses:

• MCPResource — uri, name, description, mime_type, text, blob
• MCPResourceList — resources list + server capability flags

Design Notes

• Resources are data, not actions — they don't need LLM registration (unlike tools)
• Reuses the existing persistent session from start()/close() (PR fixed MCPClient to reuse session across tool calls #4034)
• Server capability flags (subscribe, listChanged) are exposed so users can build polling or subscription logic on top
• Individual read failures in read_all_resources() are logged and skipped gracefully
• Polling, context injection, and subscriptions are intentionally left out of scope — those are application-level concerns

References

• MCP Resources spec: https://modelcontextprotocol.io/docs/concepts/resources
• Original MCP PR (MCP Service #1627) noted: "Does not handle resources, prompts, or sampling"