Module registry 

The use case: a set of tools, resources, templates and prompts that changes while sessions are using it.

The three concerns, and which file owns each

File	Concern
store	The publish. Copy the live snapshot, change one thing, swap.
subscriber	The fan-out, gated on each session’s negotiated profile.
listing	The read: one snapshot filtered for one session.

The split is the same one T10’s engine makes. A use case is a sequence of steps, and each step that could be described on its own gets a file, rather than three methods on one type that a reader has to hold in their head together.

What the swap means for a running tool

An in-flight tools/call completes against the snapshot it resolved against, even if the tool is unregistered a microsecond later. Nothing here can change that: the reader holds an owned Arc<Snapshot>, so there is no borrow for a publish to wait on, and blocking a publish until every running tool finished would let one slow tool stall every registration on the server. The alternative — cancelling in-flight calls on unregister — is a policy question, and it is not this module’s to answer.

Where the protocol lives

Nothing here names a method, a notification, or a revision. The subscriber::Subscriber is given a Feature and a method name by whoever wires the server up, because which notification means “the tool list changed” and which capability has to be advertised for it to be welcome are facts about a protocol, and this module is the part that would have to work for A2A as well as for MCP.

Examples

use protocol_droid::application::registry::RegistryStore;
use protocol_droid::domain::registry::{AuthContext, Primitive, PrimitiveKind, Tool};
use protocol_droid::domain::FeatureProfile;

let store = RegistryStore::new();
store.register(Primitive::from(Tool::new("echo", r#"{"type":"object"}"#)?));

let session = AuthContext::unrestricted("alice");
let listing = store.list_visible(&session, &FeatureProfile::all(), PrimitiveKind::Tool);

assert_eq!(listing.visible().len(), 1);
assert_eq!(listing.hidden(), 0);

Re-exports

pub use listing::Listing;

pub use store::Published;

pub use store::RegistryStore;

pub use subscriber::Fanout;

pub use subscriber::Subscriber;

pub use subscriber::SubscriberSet;

Modules

listing

The read path: a snapshot plus a session, filtered.

store

The publish side: the one place a snapshot can change.

subscriber

Telling the sessions that a list changed — and the sessions that must not be told.