Implement the in-process structured entry editor

Closes #21

crates/storage/tests/entry_documents.rs

@@ -238,11 +238,12 @@ fn atomic_save_creates_updates_and_rejects_stale_documents() -> TestResult {
     let stale_password = stale.password().expect("password").id();
     stale.update(stale_password, EntryFieldDraft::line(b"stale".to_vec())?)?;
     assert!(matches!(
-        service.save(stale, None, &mut committer),
+        service.save_recoverable(&stale, None, &mut committer),
         Err(DocumentError::Write(
             WriteError::ConcurrentModification { .. }
         ))
     ));
+    assert_eq!(stale.serialize().expose(), b"stale\nusername: alice");
     assert_eq!(
         repository.read_entry(&EntryPath::parse("documents/new")?)?,
         winner
@@ -253,9 +254,31 @@ fn atomic_save_creates_updates_and_rejects_stale_documents() -> TestResult {
     rollback.update(password, EntryFieldDraft::line(b"must roll back".to_vec())?)?;
     committer.fail = true;
     assert!(matches!(
-        service.save(rollback, None, &mut committer),
+        service.save_recoverable(&rollback, None, &mut committer),
         Err(DocumentError::Write(WriteError::Commit(_)))
     ));
+    assert!(
+        rollback
+            .serialize()
+            .expose()
+            .starts_with(b"must roll back\n")
+    );
+    assert_eq!(
+        repository.read_entry(&EntryPath::parse("documents/new")?)?,
+        winner
+    );
+    committer.fail = false;
+    std::fs::write(
+        store.path().join(".gpg-id"),
+        b"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF\n",
+    )?;
+    let retained = rollback.serialize();
+    assert!(
+        service
+            .save_recoverable(&rollback, None, &mut committer)
+            .is_err()
+    );
+    assert_eq!(rollback.serialize().expose(), retained.expose());
     assert_eq!(
         repository.read_entry(&EntryPath::parse("documents/new")?)?,
         winner