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fix(mcp): advertise ttlMs and cacheScope on list responses #287

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fix(mcp): advertise ttlMs and cacheScope on list responses #287

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42 changes: 22 additions & 20 deletions src/mcp/rmcp_server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,11 +8,11 @@ use lab_auth::AuthContext;
use rmcp::{
ErrorData, RoleServer, ServerHandler,
model::{
Annotations, CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
EmbeddedResource, GetPromptRequestParams, GetPromptResponse, GetPromptResult,
Annotations, CacheScope, CallToolRequestParams, CallToolResponse, CallToolResult,
ContentBlock, EmbeddedResource, GetPromptRequestParams, GetPromptResponse, GetPromptResult,
Implementation, ListPromptsResult, ListResourcesResult, ListToolsResult, MetaObject,
PaginatedRequestParams, ReadResourceRequestParams, ReadResourceResponse,
ReadResourceResult, Resource, ResourceContents, Role, ServerCapabilities, ServerInfo, Tool,
PaginatedRequestParams, ReadResourceRequestParams, ReadResourceResponse, ReadResourceResult,
Resource, ResourceContents, Role, ServerCapabilities, ServerInfo, Tool,
},
service::RequestContext,
transport::streamable_http_server::{
Expand All @@ -28,6 +28,11 @@ use super::actions;
use super::prompts::{get_prompt, prompt_definitions};
use super::{AppState, AuthPolicy, schemas::tool_definitions, tools::execute_tool};

/// Freshness advertised on tools/resources/prompts lists. The 2026-07-28 MCP
/// spec makes `ttlMs` and `cacheScope` mandatory; the lists only change when
/// the server binary does, and are auth-gated, so clients cache them privately.
const LIST_CACHE_TTL_MS: u64 = 60_000;

#[derive(Clone)]
pub struct CortexRmcpServer {
state: AppState,
Expand Down Expand Up @@ -55,10 +60,9 @@ impl ServerHandler for CortexRmcpServer {

let tools = rmcp_tool_definitions()?;
tracing::info!(tool_count = tools.len(), "MCP tools listed");
Ok(ListToolsResult {
tools,
..Default::default()
})
Ok(ListToolsResult::with_all_items(tools)
.with_ttl_ms(LIST_CACHE_TTL_MS)
.with_cache_scope(CacheScope::Private))
}

async fn call_tool(
Expand Down Expand Up @@ -180,14 +184,13 @@ impl ServerHandler for CortexRmcpServer {
context: RequestContext<RoleServer>,
) -> Result<ListResourcesResult, ErrorData> {
require_auth_context(&self.state, &context)?;
Ok(ListResourcesResult {
resources: vec![
schema_resource(),
prompt_output_schema_resource(),
query_widget_resource(),
],
..Default::default()
})
Ok(ListResourcesResult::with_all_items(vec![
schema_resource(),
prompt_output_schema_resource(),
query_widget_resource(),
])
.with_ttl_ms(LIST_CACHE_TTL_MS)
.with_cache_scope(CacheScope::Private))
}

async fn read_resource(
Expand Down Expand Up @@ -237,10 +240,9 @@ impl ServerHandler for CortexRmcpServer {
require_auth_context(&self.state, &context)?;
let prompts = prompt_definitions();
tracing::info!(prompt_count = prompts.len(), "MCP prompts listed");
Ok(ListPromptsResult {
prompts,
..Default::default()
})
Ok(ListPromptsResult::with_all_items(prompts)
.with_ttl_ms(LIST_CACHE_TTL_MS)
.with_cache_scope(CacheScope::Private))
}

async fn get_prompt(
Expand Down
2 changes: 2 additions & 0 deletions src/mcp/rmcp_server_tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1312,6 +1312,8 @@ async fn mounted_policy_with_auth_context_permits_tools_list() {
tools[0]["name"], "cortex",
"tools/list should return cortex tool; response: {response}"
);
assert_eq!(response["result"]["ttlMs"], 60_000, "{response}");
assert_eq!(response["result"]["cacheScope"], "private", "{response}");
}

#[tokio::test]
Expand Down