consolidate checkout status handling and improve git detection

packages/app/src/components/git-diff-pane.tsx

@@ -791,7 +791,11 @@ export function GitDiffPane({ serverId, agentId, cwd }: GitDiffPaneProps) {
     (isDiffError && diffError instanceof Error ? diffError.message : null);
   const prErrorMessage = prPayloadError?.message ?? null;
   const branchLabel =
-    gitStatus?.currentBranch ?? (notGit ? "Not a git repository" : "Unknown");
+    gitStatus?.currentBranch && gitStatus.currentBranch !== "HEAD"
+      ? gitStatus.currentBranch
+      : notGit
+        ? "Not a git repository"
+        : "Unknown";
   const actionsDisabled = !isGit || Boolean(status?.error) || isStatusLoading;
   const aheadCount = gitStatus?.aheadBehind?.ahead ?? 0;
   const aheadOfOrigin = gitStatus?.aheadOfOrigin ?? 0;

packages/app/src/components/grouped-agent-list.tsx

@@ -440,7 +440,11 @@ export function GroupedAgentList({
       });
       const checkout = checkoutQuery.data ?? null;
       const activeBranchLabel = checkout?.isGit
-        ? (checkout.currentBranch ?? checkout.baseRef ?? "git")
+        ? ((checkout.currentBranch && checkout.currentBranch !== "HEAD"
+            ? checkout.currentBranch
+            : null) ??
+          checkout.baseRef ??
+          "git")
         : null;
 
       const canArchive = !isRunning && !agent.requiresAttention;