fix(desktop): stop showing /dev/null in diff labels, keep type badge visible

desktop/src/features/messages/lib/parseDiff.ts

@@ -33,15 +33,59 @@ export function parseUnifiedDiff(content: string): ParsedDiffResult {
   }
 }
 
+export const DIFF_TYPE_LABELS: Record<DiffType, string> = {
+  add: "New file",
+  copy: "Copied",
+  delete: "Deleted",
+  modify: "Modified",
+  rename: "Renamed",
+};
+
 export function getDiffFileLabel(
   file: FileData,
   fallbackFilePath?: string,
 ): string {
-  if (file.oldPath && file.newPath && file.oldPath !== file.newPath) {
-    return `${file.oldPath} -> ${file.newPath}`;
+  const oldPath = file.oldPath === "/dev/null" ? undefined : file.oldPath;
+  const newPath = file.newPath === "/dev/null" ? undefined : file.newPath;
+
+  if (oldPath && newPath && oldPath !== newPath) {
+    return `${oldPath} -> ${newPath}`;
+  }
+
+  return newPath || oldPath || fallbackFilePath || "diff";
+}
+
+export function shouldShowDiffFileHeader(
+  label: string,
+  fileCount: number,
+  fallbackFilePath?: string,
+): boolean {
+  return fileCount > 1 || !fallbackFilePath || label !== fallbackFilePath;
+}
+
+/**
+ * Badge for the diff card's title bar. Set only when the diff is a single
+ * file whose per-file header is collapsed (its label just repeats the card
+ * title) and whose change type is notable — so "New file"/"Deleted" isn't
+ * lost with the header.
+ */
+export function getDiffTitleBadge(
+  content: string,
+  fallbackFilePath?: string,
+): string | undefined {
+  const { files } = parseUnifiedDiff(content);
+  if (files.length !== 1) {
+    return undefined;
+  }
+
+  const file = files[0];
+  const label = getDiffFileLabel(file, fallbackFilePath);
+  if (shouldShowDiffFileHeader(label, files.length, fallbackFilePath)) {
+    return undefined;
   }
 
-  return file.newPath || file.oldPath || fallbackFilePath || "diff";
+  const diffType = normalizeDiffType(file.type);
+  return diffType === "modify" ? undefined : DIFF_TYPE_LABELS[diffType];
 }
 
 export function countDiffFileChanges(file: FileData) {

desktop/src/features/messages/ui/DiffMessage.tsx

@@ -1,6 +1,7 @@
 import * as React from "react";
 import { FileDiff, Maximize2 } from "lucide-react";
 
+import { getDiffTitleBadge } from "@/features/messages/lib/parseDiff";
 import { isSafeUrl } from "@/shared/lib/url";
 import { Button } from "@/shared/ui/button";
 import { useSmoothCorners } from "@/shared/ui/smoothCorners";
@@ -39,6 +40,11 @@ export default function DiffMessage({
 
   const safeRepoUrl = isSafeUrl(repoUrl) ? repoUrl : undefined;
 
+  const titleBadge = React.useMemo(
+    () => getDiffTitleBadge(content, filePath),
+    [content, filePath],
+  );
+
   const commitUrl =
     safeRepoUrl && commitSha ? `${safeRepoUrl}/commit/${commitSha}` : undefined;
 
@@ -51,54 +57,61 @@ export default function DiffMessage({
     >
       <div className="flex items-center gap-2 px-3 py-2 border-b border-border/50 bg-muted/40">
         <FileDiff className="h-4 w-4 shrink-0 text-muted-foreground" />
-        <span className="flex-1 truncate font-mono text-xs text-foreground/80">
+        <span className="min-w-0 truncate font-mono text-xs text-foreground/80">
           {filePath ?? "diff"}
         </span>
-        {shortSha && (
-          <span className="text-xs text-muted-foreground font-mono">
-            {commitUrl ? (
+        {titleBadge && (
+          <span className="shrink-0 rounded-md border border-border/60 px-1.5 py-0.5 text-2xs uppercase tracking-[0.14em] text-muted-foreground">
+            {titleBadge}
+          </span>
+        )}
+        <div className="ml-auto flex items-center gap-2">
+          {shortSha && (
+            <span className="text-xs text-muted-foreground font-mono">
+              {commitUrl ? (
+                <a
+                  className="hover:underline"
+                  href={commitUrl}
+                  rel="noreferrer noopener"
+                  target="_blank"
+                >
+                  {shortSha}
+                </a>
+              ) : (
+                shortSha
+              )}
+            </span>
+          )}
+          {safeRepoUrl && !commitUrl && (
+            <span className="text-xs text-muted-foreground">
               <a
                 className="hover:underline"
-                href={commitUrl}
+                href={safeRepoUrl}
                 rel="noreferrer noopener"
                 target="_blank"
               >
-                {shortSha}
+                {getHostname(safeRepoUrl)}
               </a>
-            ) : (
-              shortSha
-            )}
-          </span>
-        )}
-        {safeRepoUrl && !commitUrl && (
-          <span className="text-xs text-muted-foreground">
-            <a
-              className="hover:underline"
-              href={safeRepoUrl}
-              rel="noreferrer noopener"
-              target="_blank"
-            >
-              {getHostname(safeRepoUrl)}
-            </a>
-          </span>
-        )}
-        {onExpand && (
-          <Tooltip>
-            <TooltipTrigger asChild>
-              <Button
-                aria-label="Expand diff"
-                className="h-6 w-6 p-0 text-muted-foreground hover:text-foreground"
-                onClick={onExpand}
-                size="sm"
-                type="button"
-                variant="ghost"
-              >
-                <Maximize2 className="h-4 w-4" />
-              </Button>
-            </TooltipTrigger>
-            <TooltipContent>Expand diff</TooltipContent>
-          </Tooltip>
-        )}
+            </span>
+          )}
+          {onExpand && (
+            <Tooltip>
+              <TooltipTrigger asChild>
+                <Button
+                  aria-label="Expand diff"
+                  className="h-6 w-6 p-0 text-muted-foreground hover:text-foreground"
+                  onClick={onExpand}
+                  size="sm"
+                  type="button"
+                  variant="ghost"
+                >
+                  <Maximize2 className="h-4 w-4" />
+                </Button>
+              </TooltipTrigger>
+              <TooltipContent>Expand diff</TooltipContent>
+            </Tooltip>
+          )}
+        </div>
       </div>
 
       {description && (

desktop/src/features/messages/ui/DiffMessageExpanded.tsx

@@ -1,6 +1,7 @@
 import { Rows3, SplitSquareVertical } from "lucide-react";
-import { useState } from "react";
+import { useMemo, useState } from "react";
 
+import { getDiffTitleBadge } from "@/features/messages/lib/parseDiff";
 import { DiffViewer } from "@/features/messages/ui/DiffViewer";
 import { Button } from "@/shared/ui/button";
 import {
@@ -23,6 +24,11 @@ export default function DiffMessageExpanded({
 }: DiffMessageExpandedProps) {
   const [viewType, setViewType] = useState<"split" | "unified">("unified");
 
+  const titleBadge = useMemo(
+    () => getDiffTitleBadge(content, filePath),
+    [content, filePath],
+  );
+
   return (
     <Dialog
       onOpenChange={(open) => {
@@ -33,10 +39,15 @@ export default function DiffMessageExpanded({
       <DialogContent className="max-w-5xl w-full h-[80vh] flex flex-col p-0 gap-0">
         <DialogHeader className="shrink-0 border-b border-border/50 px-4 py-3 pr-14">
           <div className="flex flex-wrap items-center gap-2">
-            <DialogTitle className="min-w-0 flex-1 truncate font-mono text-sm font-medium">
+            <DialogTitle className="min-w-0 truncate font-mono text-sm font-medium">
               {filePath ?? "Diff Viewer"}
             </DialogTitle>
-            <div className="flex items-center gap-1 rounded-lg border border-border/60 bg-muted/30 p-1">
+            {titleBadge && (
+              <span className="shrink-0 rounded-md border border-border/60 px-1.5 py-0.5 text-2xs uppercase tracking-[0.14em] text-muted-foreground">
+                {titleBadge}
+              </span>
+            )}
+            <div className="ml-auto flex items-center gap-1 rounded-lg border border-border/60 bg-muted/30 p-1">
               <Button
                 className="h-7 px-2"
                 onClick={() => {

desktop/src/features/messages/ui/DiffViewer.tsx

@@ -4,9 +4,11 @@ import { useMemo } from "react";
 
 import {
   countDiffFileChanges,
+  DIFF_TYPE_LABELS,
   getDiffFileLabel,
   normalizeDiffType,
   parseUnifiedDiff,
+  shouldShowDiffFileHeader,
 } from "@/features/messages/lib/parseDiff";
 import { cn } from "@/shared/lib/cn";
 import "./DiffViewer.css";
@@ -18,14 +20,6 @@ type DiffViewerProps = {
   className?: string;
 };
 
-const DIFF_TYPE_LABELS = {
-  add: "New file",
-  copy: "Copied",
-  delete: "Deleted",
-  modify: "Modified",
-  rename: "Renamed",
-} as const;
-
 function FileChangeBadge({
   tone,
   value,
@@ -79,10 +73,13 @@ export function DiffViewer({
       <div className="space-y-3">
         {files.map((file) => {
           const label = getDiffFileLabel(file, fallbackFilePath);
-          const showFileHeader =
-            files.length > 1 || !fallbackFilePath || label !== fallbackFilePath;
           const { additions, deletions } = countDiffFileChanges(file);
           const diffType = normalizeDiffType(file.type);
+          const showFileHeader = shouldShowDiffFileHeader(
+            label,
+            files.length,
+            fallbackFilePath,
+          );
           const fileKey = [
             file.oldPath || "",
             file.newPath || "",