fix: capture ticket edit preimages atomically

crates/ticket/src/lib.rs

@@ -1915,6 +1915,15 @@ pub trait TicketBackend {
         Ok((reference, ticket))
     }
     fn edit_item(&self, id: TicketIdOrSlug, edit: TicketItemEdit) -> Result<Ticket>;
+    fn edit_item_with_snapshots(
+        &self,
+        id: TicketIdOrSlug,
+        edit: TicketItemEdit,
+    ) -> Result<(Ticket, Ticket)> {
+        let previous = self.show(id.clone())?;
+        let current = self.edit_item(id, edit)?;
+        Ok((previous, current))
+    }
     fn dependency_check(&self, id: TicketIdOrSlug) -> Result<TicketDependencyCheck>;
     fn add_event(&self, id: TicketIdOrSlug, event: NewTicketEvent) -> Result<()>;
     fn add_state_changed(&self, id: TicketIdOrSlug, change: TicketStateChange) -> Result<()>;
@@ -3189,6 +3198,15 @@ impl TicketBackend for SqliteTicketBackend {
     }
 
     fn edit_item(&self, id: TicketIdOrSlug, edit: TicketItemEdit) -> Result<Ticket> {
+        self.edit_item_with_snapshots(id, edit)
+            .map(|(_, current)| current)
+    }
+
+    fn edit_item_with_snapshots(
+        &self,
+        id: TicketIdOrSlug,
+        edit: TicketItemEdit,
+    ) -> Result<(Ticket, Ticket)> {
         self.with_write(|conn| {
             edit.validate_body_edit_request()?;
             if !edit.has_changes() {
@@ -3204,8 +3222,9 @@ impl TicketBackend for SqliteTicketBackend {
                 validate_required_event_value("author", author)?;
             }
             let ticket_id = self.resolve_ticket_id(conn, id)?;
+            let previous = self.load_ticket(conn, &ticket_id)?;
             if edit.targets.is_some() {
-                let current = self.load_ticket(conn, &ticket_id)?.meta.workflow_state;
+                let current = previous.meta.workflow_state;
                 if current != TicketWorkflowState::Planning {
                     return Err(TicketError::Conflict(format!(
                         "ticket implementation target is locked after planning (current state: {})",
@@ -3286,7 +3305,8 @@ impl TicketBackend for SqliteTicketBackend {
             };
             let event = TicketEvent { kind: TicketEventKind::Other("item_edit".to_string()), author: Some(edit.author.unwrap_or_else(default_author)), at: Some(now), status: None, from: None, to: None, reason: None, state_field: None, heading: Some("Item edit".to_string()), body, references: Vec::new(), attributes };
             self.insert_event(conn, &ticket_id, &event)?;
-            self.load_ticket(conn, &ticket_id)
+            let current = self.load_ticket(conn, &ticket_id)?;
+            Ok((previous, current))
         })
     }
 

crates/ticket/src/tool.rs

@@ -276,6 +276,14 @@ impl TicketBackend for TicketToolBackend {
         self.backend.edit_item(id, edit)
     }
 
+    fn edit_item_with_snapshots(
+        &self,
+        id: TicketIdOrSlug,
+        edit: crate::TicketItemEdit,
+    ) -> TicketResult<(Ticket, Ticket)> {
+        self.backend.edit_item_with_snapshots(id, edit)
+    }
+
     fn dependency_check(&self, id: TicketIdOrSlug) -> TicketResult<crate::TicketDependencyCheck> {
         self.backend.dependency_check(id)
     }