matrix-mcp: auto-join only on accounts that live on the swarm homeserver

docs/4-implementation/agent-tools/matrix.md

@@ -35,10 +35,12 @@ is what an agent reads at call time. They fall into four groups:
   `join_room`. `resolve_invite` accepts or rejects a pending invite and is the
   path for invites; `join_room` is for a public room the agent wasn't invited to.
   `list_invites` gives the inviter and the topic, so an agent can judge an
-  invite before it answers. The daemon joins an invite from a user of the
-  agent's own homeserver by itself, with an info log line and no todo. An invite
-  from any other homeserver stays a todo that names the inviter as an external
-  matrix user, and the agent decides. If an automatic join fails, the invite
+  invite before it answers. On an account that lives on the swarm
+  homeserver, the daemon joins an invite from a user of that same server by itself,
+  with an info log line and no todo. Every other invite stays a todo that names the
+  inviter as an external matrix user, and the agent decides: that covers invites from
+  other homeservers and every invite to a linked account on a public server such as
+  matrix.org. If an automatic join fails, the invite
   falls back to a todo too.
 - **Receipts:** `mark_read` advances the read receipt.
 

hive-matrix-mcp/src/timeline.rs

@@ -130,7 +130,7 @@ pub async fn sweep_invites<S: BuildHasher>(
     // from the unread sweep's `<room>` key) so the two never collide; the
     // harness coalesces the wake iff the summary is new or changed, so
     // re-upserting an unchanged invite every tick is a cheap no-op.
-    let own_server = client.user_id().map(|u| u.server_name().to_owned());
+    let own_server = swarm_server(client);
     for room in &current {
         let room_id = room.room_id().to_owned();
         let inviter = room
@@ -139,8 +139,8 @@ pub async fn sweep_invites<S: BuildHasher>(
             .ok()
             .and_then(|d| d.inviter)
             .map(|m| m.user_id().to_owned());
-        // An invite from the swarm's own homeserver is trusted: join it
-        // without waking the agent. A failed join falls through to the todo
+        // An invite from a user of the swarm's own homeserver, to an account
+        // that lives on it, is trusted: join it without waking the agent. A failed join falls through to the todo
         // below, so the invite is never lost.
         if is_local(own_server.as_deref(), inviter.as_deref()) {
             match room.join().await {
@@ -179,8 +179,25 @@ pub async fn sweep_invites<S: BuildHasher>(
     }
 }
 
-/// Whether `inviter` is a user of the agent's own homeserver. No known
-/// inviter or no known own server counts as external.
+/// The swarm homeserver's server name when `client` is an account on it, else
+/// `None`. The swarm homeserver is the daemon-wide `HIVE_MATRIX_URL`; a linked
+/// account on another server (matrix.org, catgirl.cloud, ...) is not on it, so
+/// its same-server inviters are strangers, not swarm members.
+fn swarm_server(client: &Client) -> Option<matrix_sdk::ruma::OwnedServerName> {
+    let swarm = reqwest::Url::parse(&crate::paths::homeserver_url()?).ok()?;
+    same_homeserver(&swarm, &client.homeserver())
+        .then(|| client.user_id().map(|u| u.server_name().to_owned()))
+        .flatten()
+}
+
+/// Whether two homeserver URLs point at the same host and port.
+fn same_homeserver(a: &reqwest::Url, b: &reqwest::Url) -> bool {
+    a.host_str() == b.host_str() && a.port_or_known_default() == b.port_or_known_default()
+}
+
+/// Whether `inviter` is a user of the swarm homeserver `own` (the account's
+/// server when the account is on it, else `None`). No known inviter or no
+/// swarm server counts as external.
 fn is_local(own: Option<&ServerName>, inviter: Option<&UserId>) -> bool {
     matches!((own, inviter), (Some(own), Some(u)) if u.server_name() == own)
 }
@@ -197,7 +214,7 @@ pub(crate) fn invite_key(room_id: &matrix_sdk::ruma::RoomId) -> String {
 mod invite_tests {
     use matrix_sdk::ruma::{server_name, user_id};
 
-    use super::is_local;
+    use super::{is_local, same_homeserver};
 
     #[test]
     fn only_an_inviter_on_the_own_homeserver_is_local() {
@@ -216,4 +233,28 @@ mod invite_tests {
         assert!(!is_local(Some(own), None));
         assert!(!is_local(None, Some(user_id!("@mara:pr1ma.darkest.space"))));
     }
+
+    #[test]
+    fn an_account_is_on_the_swarm_homeserver_only_by_host_and_port() {
+        let u = |s: &str| reqwest::Url::parse(s).expect("url");
+        let swarm = u("https://matrix.pr1ma.darkest.space");
+        assert!(same_homeserver(
+            &swarm,
+            &u("https://matrix.pr1ma.darkest.space/")
+        ));
+        assert!(same_homeserver(
+            &swarm,
+            &u("https://matrix.pr1ma.darkest.space:443")
+        ));
+        // A public server is a different host, and a different port is a
+        // different server.
+        assert!(!same_homeserver(&swarm, &u("https://catgirl.cloud")));
+        assert!(!same_homeserver(
+            &swarm,
+            &u("https://matrix.pr1ma.darkest.space:8448")
+        ));
+        // An external account gets no swarm server, so even its own
+        // same-server inviter is not local.
+        assert!(!is_local(None, Some(user_id!("@x:catgirl.cloud"))));
+    }
 }