spaces: leaving a room says so, so an owner stops publishing a seat nobody sits in

src-tauri/src/inbox.rs

@@ -54,6 +54,7 @@ pub enum Cargo {
     SpaceKey(SpaceKeyCargo),
     ProposalPing(ProposalPing),
     SpaceJoin(SpaceJoin),
+    SpaceLeave(SpaceLeave),
 }
 
 /// The answer to an invitation: "here is the key I will wear in your Space."
@@ -68,6 +69,18 @@ pub struct SpaceJoin {
     pub proof: Vec<u8>,
 }
 
+/// "I am giving up my seat." The owner cannot see a member walk away — the
+/// roster is theirs to publish — so leaving says so, sealed. `worn` is the key
+/// on the roster, and `proof` is signed BY that key: holding the seat is the
+/// whole authority to vacate it.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SpaceLeave {
+    pub space_id: [u8; 16],
+    pub owner: [u8; 32],
+    pub worn: [u8; 32],
+    pub proof: Vec<u8>,
+}
+
 /// "Someone put a proposal on your playlist's board." Carries only enough to
 /// name it in a toast — the board itself stays the truth, and this is a
 /// best-effort nudge: the proposal stands whether or not the ping lands.
@@ -507,6 +520,7 @@ async fn dispatch(app: &tauri::AppHandle, sender: [u8; 32], cargo: Cargo) {
         Cargo::SpaceKey(k) => crate::spaces::on_inbox_space_key(app, sender, k).await,
         Cargo::ProposalPing(p) => crate::proposals::on_inbox_proposal(app, sender, p),
         Cargo::SpaceJoin(j) => crate::spaces::on_inbox_join(app, sender, j).await,
+        Cargo::SpaceLeave(l) => crate::spaces::on_inbox_leave(app, sender, l).await,
     }
 }
 
@@ -572,8 +586,15 @@ mod tests {
             room_key: [10u8; 32],
             proof: vec![1, 2, 3],
         });
+        let leave = Cargo::SpaceLeave(SpaceLeave {
+            space_id: [11u8; 16],
+            owner: [12u8; 32],
+            worn: [13u8; 32],
+            proof: vec![4, 5, 6],
+        });
         assert_eq!(index(&ping), 6, "a new variant must be appended, never inserted");
         assert_eq!(index(&join), 7, "a new variant must be appended, never inserted");
+        assert_eq!(index(&leave), 8, "a new variant must be appended, never inserted");
 
         let back: Cargo = bincode::deserialize(&bincode::serialize(&ping).unwrap()).unwrap();
         match back {