Spring AI MCP server exposes resource templates but does not support resource subscriptions in streamable sync WebMVC setup

Bug description
When using Spring AI MCP server with:

• Spring AI 2.0.0-M5
• protocol STREAMABLE
• server type SYNC
• transport WEBMVC

the server correctly exposes MCP resources/resource templates, but does not support resources/subscribe.

This makes notifyResourcesUpdated(...) effectively unusable for standard MCP clients expecting resource subscriptions.

Environment

spring.ai.mcp.server.annotation-scanner.enabled=true
spring.ai.mcp.server.enabled=true
spring.ai.mcp.server.protocol=STREAMABLE
spring.ai.mcp.server.streamable-http.mcp-endpoint=/mcp
spring.ai.mcp.server.type=SYNC
spring.ai.mcp.server.transport=WEBMVC

Observed behavior
The server starts correctly and answers initialize.

Returned capabilities are:

{
  "completions": {},
  "logging": {},
  "prompts": { "listChanged": true },
  "resources": { "subscribe": false, "listChanged": true },
  "tools": { "listChanged": true }
}

The server exposes resource templates correctly after manual registration, and resources/read works.

However, calling:

{
  "jsonrpc": "2.0",
  "id": 3,
  "method": "resources/subscribe",
  "params": {
    "uri": "user-info://users/TBE/infos"
  }
}

returns:

{
  "jsonrpc":"2.0",
  "id":3,
  "error":{
    "code":-32601,
    "message":"Method not found: resources/subscribe"
  }
}

Additional observation
On the server side, calling:

mcpSyncServer.notifyResourcesUpdated(new McpSchema.ResourcesUpdatedNotification(uri));

produces logs such as:
No sessions subscribed to resource URI: user-info://users/TBE/infos

but there is no standard way for clients to subscribe because resources.subscribe=false and resources/subscribe is not available.

Expected behavior
One of the following should be clarified or fixed:

1- If sync streamable WebMVC servers are supposed to support resource subscriptions, then resources/subscribe should be available and initialize.capabilities.resources.subscribe should be true.

2- If resource subscriptions are intentionally unsupported in this setup, then:

• this should be documented
• notifyResourcesUpdated(...) should probably not suggest a usable subscription flow for standard MCP clients in this mode

Notes
I first tried with @McpResource(uri = "user-info://users/{username}/infos"), but resource templates were not published in my setup. I worked around that by manually registering a SyncResourceTemplateSpecification, and then resources/templates/list and resources/read worked correctly.

So this issue is specifically about resource subscription support/capability, not about basic MCP connectivity.

Start with the SYNC + STREAMABLE + WEBMVC server's initialization capability reporting and request dispatch for resources/subscribe, then trace mcpSyncServer.notifyResourcesUpdated(...). Done means the chosen behavior is consistent: supported mode advertises and accepts subscriptions, or unsupported mode is documented and does not present notification as a usable client flow.