MCP: expose granular FastMCP response-caching controls

[lhpaoletti]

Problem

Superset's MCP cache adapter exposes TTLs and a tool exclusion list, but it does not expose FastMCP's full per-operation controls.

FastMCP supports enabling/disabling each cached operation and using allowlists or exclusion lists for individual items:

https://fastmcp.mintlify.app/servers/middleware#caching

Superset currently maps only TTL values and excluded_tools into ResponseCachingMiddleware:

https://github.com/apache/superset/blob/master/superset/mcp_service/caching.py#L30-L77

This makes a safe “cache only static MCP metadata” configuration difficult. In particular:

• there is no per-operation enabled setting;
• included_tools allowlists are not forwarded;
• max_item_size is declared in MCP_CACHE_CONFIG, but is not consumed by the adapter;
• when tool search is enabled, clients invoke the synthetic call_tool proxy, so excluding a target tool name alone may not reliably prevent caching of the
  proxy invocation.

Proposal

Expand MCP_CACHE_CONFIG to expose FastMCP's operation-level controls for:

• tools/list
• resources/list
• prompts/list
• resources/read
• prompts/get
• tools/call

The configuration should support each operation's enabled, ttl, and applicable included_* / excluded_* controls.

For tool search, cache policy should be evaluated against the resolved target tool, or call_tool caching should remain disabled by default.

max_item_size should either be wired to a supported implementation or removed from the documented configuration to avoid implying it is enforced.

Why this is safer

This would allow a safe enabled profile that caches only static protocol metadata, for example tools/list, resources/list, and prompts/list, while
leaving tools/call disabled by default.

It avoids relying on a growing denylist of mutable or authorization-sensitive tools and gives operators an explicit, auditable way to opt in to narrow caching.

Related implementation points:

• https://github.com/apache/superset/blob/master/superset/mcp_service/mcp_config.py#L171-L187
• https://github.com/apache/superset/blob/master/superset/mcp_service/caching.py
• https://github.com/apache/superset/blob/master/superset/mcp_service/server.py#L422-L505

Disclaimer: This discussion was prepared by an AI agent on behalf of Luis Paoletti (lh.paoletti@gmail.com).