Replace resources/subscribe with subscriptions/listen to receive MCP list-changed and resource-update notifications

Documented steps

1. Read https://modelcontextprotocol.io/specification/2026-07-28/basic/patterns/subscriptions — subscriptions/listen replaces both the resources/subscribe RPC and the HTTP GET SSE endpoint.
2. Client: POST a long-lived JSON-RPC request with method 'subscriptions/listen'. The response stream stays open and carries notifications until the client cancels.
3. Opt into specific notification types via the params 'notifications' object. All fields are optional; omitting a field means not subscribed.
4. Set 'toolsListChanged': true to receive notifications/tools/list_changed.
5. Set 'promptsListChanged': true to receive notifications/prompts/list_changed.
6. Set 'resourcesListChanged': true to receive notifications/resources/list_changed.
7. Set 'resourceSubscriptions' to a string array of resource URIs to receive notifications/resources/updated for those URIs.
8. Server: send notifications/subscriptions/acknowledged as the FIRST message on the stream, carrying the subscription id in _meta['io.modelcontextprotocol/subscriptionId'], and echoing in 'notifications' the subset you agreed to honor. Send nothing else before the ack.
9. Server: tag every notification on the stream with _meta['io.modelcontextprotocol/subscriptionId'], whose value is the JSON-RPC id of the originating subscriptions/listen request.
10. Server: MUST NOT send notification types the client did not explicitly request.
11. Client: use the subscriptionId to demultiplex, which is mandatory on stdio where multiple subscriptions share one channel and messages may interleave.
12. Cancel by closing the SSE response stream (Streamable HTTP) or by sending notifications/cancelled referencing the subscriptions/listen request id (stdio).
13. Server: when ending a subscription on your own initiative, respond to the original subscriptions/listen request with an empty result ({resultType:'complete', _meta:{subscriptionId}}) before closing, so the client can distinguish a graceful end from a transport drop.
14. Keep long-lived streams alive with SSE comment keepalives and set X-Accel-Buffering: no.
15. Verify: open two concurrent subscriptions, confirm each ack arrives first with distinct ids, confirm notifications are tagged correctly, and confirm a resource change fires only on the subscription that asked for it.