fix(models): let a snapshot race resolve to the version that won

Two sends of the same request can both miss the content-hash lookup and race to
insert. The unique index settles it; the loser wants exactly what the winner
wrote, not an error that costs its response a version link.

apps/yaak-client/components/RequestVersionDropdown.tsx

@@ -21,8 +21,8 @@ interface Props {
  * existed have no version and stay quiet forever.
  */
 export function RequestVersionDropdown({ response }: Props) {
-  const comparison = useRequestVersion(response.versionId, response.requestId);
-  if (comparison.data == null || !comparison.data.differs) {
+  const { data: comparison } = useRequestVersion(response.versionId, response.requestId);
+  if (comparison == null || !comparison.differs) {
     return null;
   }
 
@@ -32,12 +32,12 @@ export function RequestVersionDropdown({ response }: Props) {
         {
           label: "View Diff",
           leftSlot: <Icon icon="git_branch" />,
-          onSelect: () => showRequestVersionDiff(comparison.data!),
+          onSelect: () => showRequestVersionDiff(comparison),
         },
         {
           label: "Restore This Version",
           leftSlot: <Icon icon="history" />,
-          onSelect: () => restoreRequestVersion(comparison.data!.version),
+          onSelect: () => restoreRequestVersion(comparison.version),
         },
       ]}
     >

crates/yaak-models/src/queries/model_versions.rs

@@ -50,11 +50,22 @@ impl<'a> ClientDb<'a> {
             workspace_id: request.workspace_id().to_string(),
             model_type: request.model_type().to_string(),
             model_id: request.id().to_string(),
-            content_hash,
+            content_hash: content_hash.clone(),
             document,
             reason,
             ..Default::default()
-        })?;
+        });
+
+        let version = match version {
+            Ok(version) => version,
+            // Two sends of the same request can both miss the lookup above and
+            // race to insert. The unique index settles it, and the loser wants
+            // exactly what the winner wrote.
+            Err(err) => match self.find_version_by_hash(request.id(), &content_hash) {
+                Some(existing) => return Ok(existing),
+                None => return Err(err),
+            },
+        };
 
         self.prune_model_versions(request.id())?;