fix: deletable self-sent mail, honest refused-handshake reporting, registration remedy

cli/src/main.rs

@@ -174,7 +174,9 @@ fn hint(error: Option<&fumi::error::Error>) {
             }
         }
         Some(fumi::error::Error::NotRegistered) => {
-            eprintln!("run: fumi register <user@host>")
+            eprintln!(
+                "for a new mailbox:\n  fumi register <user@host>\nfor an existing one, pin the server and restore:\n  fumi trust <host> <key>\n  fumi restore <user@host>"
+            )
         }
         _ => {}
     }
@@ -675,11 +677,17 @@ fn resolve_id_prefixes(store: &Store, ids: &[String]) -> Result<Vec<[u8; ID_LEN]
     let mut full = Vec::with_capacity(ids.len());
     for id in ids {
         let prefix = id.to_ascii_lowercase();
-        let matches: Vec<[u8; ID_LEN]> = stored
+        let mut matches: Vec<[u8; ID_LEN]> = stored
             .iter()
             .filter(|m| hex(m).starts_with(&prefix))
             .copied()
             .collect();
+        // A self-addressed message is stored once as received and once as
+        // sent with the same id; identical ids across folders are one
+        // message by construction, so dedupe before requiring more
+        // specificity.
+        matches.sort_unstable();
+        matches.dedup();
         match matches.len() {
             0 => return Err(anyhow!(format!("no message matching {id:?}"))),
             1 => full.push(matches[0]),
@@ -887,4 +895,30 @@ mod tests {
         assert_eq!(format_utc(951_782_400), "2000-02-29 00:00"); // leap day
         assert_eq!(format_utc(-1), "1969-12-31 23:59");
     }
+
+    /// A self-addressed message sits in the inbox and the sent folder with
+    /// the same id; resolving it must yield one message, not an ambiguity.
+    #[test]
+    fn id_resolution_treats_a_self_addressed_message_as_one() {
+        let store = Store::open_in_memory().unwrap();
+        let id = [7u8; ID_LEN];
+        store.store_inbox(&id, b"envelope", 1, false, false).unwrap();
+        store.store_sent(&id, "fumi@localhost", b"envelope", 1).unwrap();
+        let full = resolve_id_prefixes(&store, &[hex(&id)]).unwrap();
+        assert_eq!(full, vec![id]);
+    }
+
+    /// Genuinely distinct messages sharing a prefix must still demand a
+    /// more specific id.
+    #[test]
+    fn id_resolution_rejects_an_ambiguous_prefix() {
+        let store = Store::open_in_memory().unwrap();
+        let a = [7u8; ID_LEN];
+        let mut b = [7u8; ID_LEN];
+        b[31] = 8;
+        store.store_inbox(&a, b"a", 1, false, false).unwrap();
+        store.store_inbox(&b, b"b", 2, false, false).unwrap();
+        assert!(resolve_id_prefixes(&store, &["0707".into()]).is_err());
+        assert_eq!(resolve_id_prefixes(&store, &[hex(&a)]).unwrap(), vec![a]);
+    }
 }