Implement the in-process structured entry editor

Closes #21

crates/storage/src/document.rs

@@ -262,6 +262,33 @@ impl EntryDocument {
             .ok_or(DocumentError::UnknownField { id })
     }
 
+    /// Replace only a structured field's value while preserving its storage-
+    /// supplied name and syntax.
+    pub fn replace_field_value(
+        &mut self,
+        id: EntryFieldId,
+        value: Vec<u8>,
+    ) -> Result<(), DocumentError> {
+        let field = self.field(id).ok_or(DocumentError::UnknownField { id })?;
+        let draft = match field.metadata().kind() {
+            EntryFieldKind::OtpUri => EntryFieldDraft::otp_uri(value)?,
+            EntryFieldKind::Password | EntryFieldKind::Note | EntryFieldKind::Blank => {
+                EntryFieldDraft::line(value)?
+            }
+            EntryFieldKind::Username
+            | EntryFieldKind::Email
+            | EntryFieldKind::Url
+            | EntryFieldKind::Field => EntryFieldDraft::field(
+                field
+                    .metadata()
+                    .name()
+                    .ok_or(DocumentError::InvalidFieldName)?,
+                value,
+            )?,
+        };
+        self.update(id, draft)
+    }
+
     pub fn conflict_token(&self) -> DocumentConflictToken {
         self.conflict_token
     }
@@ -424,6 +451,26 @@ impl<'a> EntryDocumentService<'a> {
             committer,
         )?)
     }
+
+    /// Save without consuming the document, allowing an in-process editor to
+    /// present a conflict or encryption failure and retain the user's draft.
+    pub fn save_recoverable(
+        &self,
+        document: &EntryDocument,
+        signing: Option<&SigningPolicy>,
+        committer: &mut impl EntryCommitter,
+    ) -> Result<WriteOutcome, DocumentError> {
+        let replacement = document.serialize();
+        Ok(
+            VaultWriter::new(self.repository, self.keys).finish_edit_recoverable(
+                &document.session,
+                replacement,
+                "IronStorage structured editor",
+                signing,
+                committer,
+            )?,
+        )
+    }
 }
 
 #[derive(Debug)]