feat: add optional split chat/diff center layout (default off)

src-tauri/src/types.rs

@@ -586,6 +586,11 @@ pub(crate) struct AppSettings {
         rename = "notificationSoundsEnabled"
     )]
     pub(crate) notification_sounds_enabled: bool,
+    #[serde(
+        default = "default_split_chat_diff_view",
+        rename = "splitChatDiffView"
+    )]
+    pub(crate) split_chat_diff_view: bool,
     #[serde(default = "default_preload_git_diffs", rename = "preloadGitDiffs")]
     pub(crate) preload_git_diffs: bool,
     #[serde(
@@ -923,6 +928,10 @@ fn default_system_notifications_enabled() -> bool {
     true
 }
 
+fn default_split_chat_diff_view() -> bool {
+    false
+}
+
 fn default_preload_git_diffs() -> bool {
     true
 }
@@ -1184,6 +1193,7 @@ impl Default for AppSettings {
             code_font_size: default_code_font_size(),
             notification_sounds_enabled: true,
             system_notifications_enabled: true,
+            split_chat_diff_view: default_split_chat_diff_view(),
             preload_git_diffs: default_preload_git_diffs(),
             git_diff_ignore_whitespace_changes: default_git_diff_ignore_whitespace_changes(),
             commit_message_prompt: default_commit_message_prompt(),
@@ -1346,6 +1356,7 @@ mod tests {
         assert_eq!(settings.code_font_size, 11);
         assert!(settings.notification_sounds_enabled);
         assert!(settings.system_notifications_enabled);
+        assert!(!settings.split_chat_diff_view);
         assert!(settings.preload_git_diffs);
         assert!(!settings.git_diff_ignore_whitespace_changes);
         assert!(settings.commit_message_prompt.contains("{diff}"));

src/App.tsx

@@ -399,6 +399,7 @@ function MainApp() {
     activeWorkspace,
     gitDiffPreloadEnabled: appSettings.preloadGitDiffs,
     gitDiffIgnoreWhitespaceChanges: appSettings.gitDiffIgnoreWhitespaceChanges,
+    splitChatDiffView: appSettings.splitChatDiffView,
     isCompact,
     isTablet,
     activeTab,
@@ -2326,6 +2327,7 @@ function MainApp() {
         tabletTab={tabletTab}
         centerMode={centerMode}
         preloadGitDiffs={appSettings.preloadGitDiffs}
+        splitChatDiffView={appSettings.splitChatDiffView}
         hasActivePlan={hasActivePlan}
         activeWorkspace={Boolean(activeWorkspace)}
         sidebarNode={sidebarNode}

src/features/app/components/AppLayout.tsx

@@ -12,6 +12,7 @@ type AppLayoutProps = {
   tabletTab: "codex" | "git" | "log";
   centerMode: "chat" | "diff";
   preloadGitDiffs: boolean;
+  splitChatDiffView: boolean;
   hasActivePlan: boolean;
   activeWorkspace: boolean;
   sidebarNode: ReactNode;
@@ -48,6 +49,7 @@ export const AppLayout = memo(function AppLayout({
   tabletTab,
   centerMode,
   preloadGitDiffs,
+  splitChatDiffView,
   hasActivePlan,
   activeWorkspace,
   sidebarNode,
@@ -134,6 +136,7 @@ export const AppLayout = memo(function AppLayout({
       topbarLeftNode={desktopTopbarLeftNode}
       centerMode={centerMode}
       preloadGitDiffs={preloadGitDiffs}
+      splitChatDiffView={splitChatDiffView}
       messagesNode={messagesNode}
       gitDiffViewerNode={gitDiffViewerNode}
       gitDiffPanelNode={gitDiffPanelNode}

src/features/app/hooks/useGitPanelController.test.tsx

@@ -38,6 +38,7 @@ function makeProps(overrides?: Partial<Parameters<typeof useGitPanelController>[
     activeWorkspace: workspace,
     gitDiffPreloadEnabled: false,
     gitDiffIgnoreWhitespaceChanges: false,
+    splitChatDiffView: false,
     isCompact: false,
     isTablet: false,
     activeTab: "codex" as const,
@@ -142,4 +143,17 @@ describe("useGitPanelController preload behavior", () => {
     const selectedEnabled = getLastEnabledArg();
     expect(selectedEnabled).toBe(true);
   });
+
+  it("loads local diffs when split view is enabled and preload is disabled", () => {
+    renderHook(() =>
+      useGitPanelController(
+        makeProps({
+          splitChatDiffView: true,
+        }),
+      ),
+    );
+
+    const enabled = getLastEnabledArg();
+    expect(enabled).toBe(true);
+  });
 });

src/features/app/hooks/useGitPanelController.ts

@@ -9,6 +9,7 @@ export function useGitPanelController({
   activeWorkspace,
   gitDiffPreloadEnabled,
   gitDiffIgnoreWhitespaceChanges,
+  splitChatDiffView,
   isCompact,
   isTablet,
   activeTab,
@@ -21,6 +22,7 @@ export function useGitPanelController({
   activeWorkspace: WorkspaceInfo | null;
   gitDiffPreloadEnabled: boolean;
   gitDiffIgnoreWhitespaceChanges: boolean;
+  splitChatDiffView: boolean;
   isCompact: boolean;
   isTablet: boolean;
   activeTab: "home" | "projects" | "codex" | "git" | "log";
@@ -104,10 +106,13 @@ export function useGitPanelController({
   );
   const shouldLoadSelectedLocalDiff =
     centerMode === "diff" && Boolean(selectedDiffPath);
+  const shouldLoadLocalDiffsForSplitView = splitChatDiffView && diffSource === "local";
   const shouldLoadLocalDiffs =
     Boolean(activeWorkspace) &&
     (shouldPreloadDiffs ||
-      (gitDiffPreloadEnabled ? diffUiVisible : shouldLoadSelectedLocalDiff));
+      (gitDiffPreloadEnabled
+        ? diffUiVisible
+        : shouldLoadSelectedLocalDiff || shouldLoadLocalDiffsForSplitView));
   const shouldLoadDiffs =
     Boolean(activeWorkspace) &&
     (diffSource === "local" ? shouldLoadLocalDiffs : diffUiVisible);

src/features/git/components/GitDiffViewer.tsx

@@ -5,6 +5,7 @@ import { FileDiff, WorkerPoolContextProvider } from "@pierre/diffs/react";
 import type { FileDiffMetadata } from "@pierre/diffs";
 import { parsePatchFiles } from "@pierre/diffs";
 import RotateCcw from "lucide-react/dist/esm/icons/rotate-ccw";
+import GitCommitHorizontal from "lucide-react/dist/esm/icons/git-commit-horizontal";
 import { workerFactory } from "../../../utils/diffsWorker";
 import type { GitHubPullRequest, GitHubPullRequestComment } from "../../../types";
 import { formatRelativeTime } from "../../../utils/time";
@@ -594,6 +595,18 @@ export function GitDiffViewer({
     }
     rowVirtualizer.scrollToIndex(0, { align: "start" });
   }, [diffs.length, rowVirtualizer]);
+  const emptyStateCopy = pullRequest
+    ? {
+        title: "No file changes in this pull request",
+        subtitle:
+          "The pull request loaded, but there are no diff hunks to render for this selection.",
+        hint: "Try switching to another pull request or commit from the Git panel.",
+      }
+    : {
+        title: "Working tree is clean",
+        subtitle: "No local changes were detected for the current workspace.",
+        hint: "Make an edit, stage a file, or select a commit to inspect changes here.",
+      };
 
   return (
     <WorkerPoolContextProvider
@@ -654,7 +667,15 @@ export function GitDiffViewer({
           </div>
         )}
         {!error && !isLoading && !diffs.length && (
-          <div className="diff-viewer-empty">No changes detected.</div>
+          <div className="diff-viewer-empty-state" role="status" aria-live="polite">
+            <div className="diff-viewer-empty-glow" aria-hidden />
+            <span className="diff-viewer-empty-icon" aria-hidden>
+              <GitCommitHorizontal size={18} />
+            </span>
+            <h3 className="diff-viewer-empty-title">{emptyStateCopy.title}</h3>
+            <p className="diff-viewer-empty-subtitle">{emptyStateCopy.subtitle}</p>
+            <p className="diff-viewer-empty-hint">{emptyStateCopy.hint}</p>
+          </div>
         )}
         {!error && diffs.length > 0 && (
           <div

src/features/layout/components/DesktopLayout.tsx

@@ -12,6 +12,7 @@ type DesktopLayoutProps = {
   topbarLeftNode: ReactNode;
   centerMode: "chat" | "diff";
   preloadGitDiffs: boolean;
+  splitChatDiffView: boolean;
   messagesNode: ReactNode;
   gitDiffViewerNode: ReactNode;
   gitDiffPanelNode: ReactNode;
@@ -36,6 +37,7 @@ export function DesktopLayout({
   topbarLeftNode,
   centerMode,
   preloadGitDiffs,
+  splitChatDiffView,
   messagesNode,
   gitDiffViewerNode,
   gitDiffPanelNode,
@@ -50,12 +52,19 @@ export function DesktopLayout({
 }: DesktopLayoutProps) {
   const diffLayerRef = useRef<HTMLDivElement | null>(null);
   const chatLayerRef = useRef<HTMLDivElement | null>(null);
-  const shouldRenderDiffViewer = preloadGitDiffs || centerMode === "diff";
+  const shouldRenderDiffViewer =
+    splitChatDiffView || preloadGitDiffs || centerMode === "diff";
 
   useEffect(() => {
     const diffLayer = diffLayerRef.current;
     const chatLayer = chatLayerRef.current;
 
+    if (splitChatDiffView) {
+      diffLayer?.removeAttribute("inert");
+      chatLayer?.removeAttribute("inert");
+      return;
+    }
+
     if (diffLayer) {
       if (centerMode === "diff") {
         diffLayer.removeAttribute("inert");
@@ -81,7 +90,7 @@ export function DesktopLayout({
     ) {
       activeElement.blur();
     }
-  }, [centerMode]);
+  }, [centerMode, splitChatDiffView]);
 
   return (
     <>
@@ -103,21 +112,44 @@ export function DesktopLayout({
           <>
             <MainTopbar leftNode={topbarLeftNode} />
             {approvalToastsNode}
-            <div className="content">
-              <div
-                className={`content-layer ${centerMode === "diff" ? "is-active" : "is-hidden"}`}
-                aria-hidden={centerMode !== "diff"}
-                ref={diffLayerRef}
-              >
-                {shouldRenderDiffViewer ? gitDiffViewerNode : null}
-              </div>
-              <div
-                className={`content-layer ${centerMode === "chat" ? "is-active" : "is-hidden"}`}
-                aria-hidden={centerMode !== "chat"}
-                ref={chatLayerRef}
-              >
-                {messagesNode}
-              </div>
+            <div className={`content${splitChatDiffView ? " content-split" : ""}`}>
+              {splitChatDiffView ? (
+                <>
+                  <div
+                    className={`content-layer content-layer-split content-layer-chat${
+                      centerMode === "chat" ? " is-active" : ""
+                    }`}
+                    ref={chatLayerRef}
+                  >
+                    {messagesNode}
+                  </div>
+                  <div
+                    className={`content-layer content-layer-split content-layer-diff${
+                      centerMode === "diff" ? " is-active" : ""
+                    }`}
+                    ref={diffLayerRef}
+                  >
+                    {shouldRenderDiffViewer ? gitDiffViewerNode : null}
+                  </div>
+                </>
+              ) : (
+                <>
+                  <div
+                    className={`content-layer ${centerMode === "diff" ? "is-active" : "is-hidden"}`}
+                    aria-hidden={centerMode !== "diff"}
+                    ref={diffLayerRef}
+                  >
+                    {shouldRenderDiffViewer ? gitDiffViewerNode : null}
+                  </div>
+                  <div
+                    className={`content-layer ${centerMode === "chat" ? "is-active" : "is-hidden"}`}
+                    aria-hidden={centerMode !== "chat"}
+                    ref={chatLayerRef}
+                  >
+                    {messagesNode}
+                  </div>
+                </>
+              )}
             </div>
 
             <div

src/features/settings/components/SettingsView.test.tsx

@@ -68,6 +68,7 @@ const baseSettings: AppSettings = {
   codeFontSize: 11,
   notificationSoundsEnabled: true,
   systemNotificationsEnabled: true,
+  splitChatDiffView: false,
   preloadGitDiffs: true,
   gitDiffIgnoreWhitespaceChanges: false,
   commitMessagePrompt: DEFAULT_COMMIT_MESSAGE_PROMPT,
@@ -374,6 +375,29 @@ describe("SettingsView Display", () => {
     });
   });
 
+  it("toggles split chat and diff center panes", async () => {
+    const onUpdateAppSettings = vi.fn().mockResolvedValue(undefined);
+    renderDisplaySection({ onUpdateAppSettings });
+
+    const row = screen
+      .getByText("Split chat and diff center panes")
+      .closest(".settings-toggle-row") as HTMLElement | null;
+    if (!row) {
+      throw new Error("Expected split center panes row");
+    }
+    const toggle = row.querySelector("button.settings-toggle") as HTMLButtonElement | null;
+    if (!toggle) {
+      throw new Error("Expected split center panes toggle");
+    }
+    fireEvent.click(toggle);
+
+    await waitFor(() => {
+      expect(onUpdateAppSettings).toHaveBeenCalledWith(
+        expect.objectContaining({ splitChatDiffView: true }),
+      );
+    });
+  });
+
   it("toggles reduce transparency", async () => {
     const onToggleTransparency = vi.fn();
     renderDisplaySection({ onToggleTransparency, reduceTransparency: false });

src/features/settings/components/sections/SettingsDisplaySection.tsx

@@ -128,6 +128,27 @@ export function SettingsDisplaySection({
           <span className="settings-toggle-knob" />
         </button>
       </div>
+      <div className="settings-toggle-row">
+        <div>
+          <div className="settings-toggle-title">Split chat and diff center panes</div>
+          <div className="settings-toggle-subtitle">
+            Show chat and diff side by side instead of swapping between them.
+          </div>
+        </div>
+        <button
+          type="button"
+          className={`settings-toggle ${appSettings.splitChatDiffView ? "on" : ""}`}
+          onClick={() =>
+            void onUpdateAppSettings({
+              ...appSettings,
+              splitChatDiffView: !appSettings.splitChatDiffView,
+            })
+          }
+          aria-pressed={appSettings.splitChatDiffView}
+        >
+          <span className="settings-toggle-knob" />
+        </button>
+      </div>
       <div className="settings-toggle-row">
         <div>
           <div className="settings-toggle-title">Auto-generate new thread titles</div>

src/features/settings/hooks/useAppSettings.ts

@@ -72,6 +72,7 @@ function buildDefaultSettings(): AppSettings {
     codeFontSize: CODE_FONT_SIZE_DEFAULT,
     notificationSoundsEnabled: true,
     systemNotificationsEnabled: true,
+    splitChatDiffView: false,
     preloadGitDiffs: true,
     gitDiffIgnoreWhitespaceChanges: false,
     commitMessagePrompt: DEFAULT_COMMIT_MESSAGE_PROMPT,