brokerd: state.sock answers memoryd's question about a session's state

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/brokerd/src/config.rs

@@ -25,12 +25,14 @@ impl Default for Paths {
     }
 }
 
-/// An empty path means "the default under `home`".
+/// The sockets `brokerd` serves. An empty path means "the default under `home`".
 #[derive(Debug, Clone, PartialEq, Eq, Deserialize, Default)]
 #[serde(deny_unknown_fields, default)]
 pub struct Sockets {
     pub broker: PathBuf,
     pub admin: PathBuf,
+    /// `memoryd`'s session-state questions (M5c spec, section 7).
+    pub state: PathBuf,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
@@ -284,6 +286,14 @@ impl Config {
             self.sockets.admin.clone()
         }
     }
+    /// `state.sock`, where `memoryd` asks for a session's state.
+    pub fn state_socket(&self) -> PathBuf {
+        if self.sockets.state.as_os_str().is_empty() {
+            self.paths.home.join("run/memory-broker/state.sock")
+        } else {
+            self.sockets.state.clone()
+        }
+    }
     /// `gateway.sock`, when `[gateway]` is set.
     pub fn gateway_socket(&self) -> Option<PathBuf> {
         let gateway = self.gateway.as_ref()?;