From 8d11c4b0a1935ccfd8bb2069590ea658f057da03 Mon Sep 17 00:00:00 2001
From: hanafish <1106510024@qq.com>
Date: Thu, 6 Aug 2026 22:14:06 +0800
Subject: [PATCH 1/2] fix(source-control): unify diff views and focus state

---
 .../DiffViewConsistency.md                    |  74 ++++++++++
 src/engines/GitWorkflow/GitHubDiff/types.ts   |   3 +-
 src/features/CodeMirror/Diff/index.tsx        |   3 +-
 src/features/CodeViewer/GitDiffViewer.tsx     |   3 +-
 .../SourceControlHeaderContent.test.ts        |  82 +++++++++++
 .../components/SourceControlHeaderContent.tsx |  44 ++++--
 .../content/GitCommitDetailContent/index.tsx  |   4 +-
 .../content/GitDiffContent/index.tsx          |   9 +-
 .../AllChangesView.tsx                        |   7 +-
 .../SourceControlMainContent/FocusView.tsx    |  15 +-
 .../SourceControlMainContent/index.tsx        |   1 -
 .../content/SourceControlMainPane.tsx         |   7 +-
 .../__tests__/FocusView.emptyState.test.ts    |  44 ++++++
 .../content/__tests__/TEST_CASES.md           |  33 +++--
 .../__tests__/sourceControlMainProps.test.ts  |  54 +++++++
 .../content/sourceControlMainProps.ts         |  74 +++++++++-
 .../hooks/useSourceControlPaneActions.ts      |  30 +---
 .../Panels/EditorMainPane/index.tsx           |  10 +-
 .../CodeEditor/Panels/EditorMainPane/types.ts |   2 +
 .../detail/PrChangesTab.tsx                   |   4 +-
 .../CodeEditor/__tests__/TEST_CASES.md        |  11 +-
 .../sourceControlStateTransitions.test.ts     | 136 ++++++++++++++++++
 src/modules/WorkStation/CodeEditor/index.tsx  |   3 +
 .../sourceControlStateTransitions.ts          |  63 ++++++++
 .../CodeEditor/useSourceControlSetup.ts       |  21 ++-
 .../diffSessionReplay.useDetailContent.tsx    |   5 +
 .../WorkStation/Diff/SessionReplay/index.tsx  |  32 ++++-
 .../shared/DiffFileSection/index.tsx          |   5 +-
 .../shared/DiffSectionList/index.tsx          |   4 +
 .../shared/components/FileHeader/index.tsx    |   3 +-
 .../codeEditor/diffViewModeAtom.test.ts       |  42 ++++++
 .../codeEditor/diffViewModeAtom.ts            |  28 ++++
 src/store/workstation/codeEditor/index.ts     |   3 +
 src/types/git/types.ts                        |   3 +
 34 files changed, 771 insertions(+), 91 deletions(-)
 create mode 100644 docs/frontend-ui-audit-2026-08-05/DiffViewConsistency.md
 create mode 100644 src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.test.ts
 create mode 100644 src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/FocusView.emptyState.test.ts
 create mode 100644 src/modules/WorkStation/CodeEditor/__tests__/sourceControlStateTransitions.test.ts
 create mode 100644 src/modules/WorkStation/CodeEditor/sourceControlStateTransitions.ts
 create mode 100644 src/store/workstation/codeEditor/diffViewModeAtom.test.ts
 create mode 100644 src/store/workstation/codeEditor/diffViewModeAtom.ts

diff --git a/docs/frontend-ui-audit-2026-08-05/DiffViewConsistency.md b/docs/frontend-ui-audit-2026-08-05/DiffViewConsistency.md
new file mode 100644
index 000000000..508eaa580
--- /dev/null
+++ b/docs/frontend-ui-audit-2026-08-05/DiffViewConsistency.md
@@ -0,0 +1,74 @@
+# Frontend UI Audit: Diff View Consistency
+
+**Files:**
+
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/index.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainPane.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/index.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/FocusView.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/AllChangesView.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitDiffContent/index.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitCommitDetailContent/index.tsx`
+- `src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrChangesTab.tsx`
+- `src/modules/WorkStation/Diff/SessionReplay/index.tsx`
+- `src/modules/WorkStation/Diff/SessionReplay/diffSessionReplay.useDetailContent.tsx`
+- `src/modules/WorkStation/shared/DiffFileSection/index.tsx`
+- `src/modules/WorkStation/shared/DiffSectionList/index.tsx`
+- `src/modules/shared/components/FileHeader/index.tsx`
+- `src/features/CodeMirror/Diff/index.tsx`
+- `src/features/CodeViewer/GitDiffViewer.tsx`
+
+**Date:** 2026-08-05
+
+**Auditor:** Codex
+
+## D1 — Design-system component usage
+
+| Line                                   | Element                         | Verdict          | Reason                                                                                                                 | Suggested change                                                                                                     |
+| -------------------------------------- | ------------------------------- | ---------------- | ---------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------- |
+| `SourceControlHeaderContent.tsx:217`   | Unified / split selector        | keep with reason | Uses the existing `TabPill` design-system control, matching the file diff header interaction.                          | None.                                                                                                                |
+| `SessionReplay/index.tsx:269`          | Unified / split selector        | keep with reason | Uses the same `TabPill` control and shared preference as the other diff surfaces.                                      | None.                                                                                                                |
+| `GitCommitDetailContent/index.tsx:377` | Collapsed file-list rail button | keep with reason | The control occupies a full-height 24 px rail; the current design-system `Button` variants do not model that geometry. | Keep the raw semantic button until the rail pattern is abstracted.                                                   |
+| `PrChangesTab.tsx:214`                 | Collapsed file-list rail button | keep with reason | Same full-height rail geometry as commit details.                                                                      | Keep the raw semantic button until the rail pattern is abstracted.                                                   |
+| `DiffFileSection/index.tsx:418`        | Sticky expandable file header   | keep with reason | It is a full-width, multiline disclosure row rather than a standard action button.                                     | Continue using a semantic button; consider a dedicated diff-section header only if the pattern gains more consumers. |
+| `FocusView.tsx:51`                     | No-file Focus empty state       | keep with reason | Reuses the workstation `NoTabsPlaceholder` with a focused instruction instead of assembling a bespoke empty state.     | None.                                                                                                                |
+
+## D2 — Color and token usage
+
+| Line | Element                 | Verdict          | Reason                                                                                                                           | Suggested change |
+| ---- | ----------------------- | ---------------- | -------------------------------------------------------------------------------------------------------------------------------- | ---------------- |
+| —    | Audited visible changes | keep with reason | New controls use existing semantic border, fill, and text tokens; no raw colors or duplicated token expressions were introduced. | None.            |
+
+## D3 — Spacing and typography
+
+| Line                                     | Element                                       | Verdict          | Reason                                                                                                                                     | Suggested change                                                                             |
+| ---------------------------------------- | --------------------------------------------- | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------- |
+| `DiffSectionList/index.tsx:51`           | Virtual-list footer buffer `h-[100px]`        | keep with reason | This is an exact scroll affordance rather than visual component sizing, and the spacing scale has no exact 100 px token.                   | None.                                                                                        |
+| `DiffFileSection/index.tsx:321`          | Loading placeholder `h-[480px] min-h-[320px]` | fix              | Both values have exact Tailwind scale equivalents and are unrelated to the current diff-mode behavior.                                     | In a separate visual-cleanup sweep, use `h-120 min-h-80` and visually verify loading layout. |
+| `DiffFileSection/index.tsx:424`          | Chevron reservation `w-[14px]`                | keep with reason | The width deliberately matches the 14 px icon and has no exact standard spacing class.                                                     | None.                                                                                        |
+| `DiffFileSection/index.tsx:436-463`      | Dense diff metadata typography                | keep with reason | The 13 px filename and 11 px metadata match the established dense diff header hierarchy; the standard text scale has no exact equivalents. | Keep until diff typography is tokenized system-wide.                                         |
+| `SourceControlHeaderContent.tsx:119-123` | Dense source-control header typography        | keep with reason | The 11 px prefix and 13 px title preserve the existing editor-header hierarchy and were not introduced by this change.                     | Keep until editor header typography is tokenized system-wide.                                |
+
+## D4 — Accessibility basics
+
+| Line                                   | Element                            | Verdict          | Reason                                                                                                      | Suggested change                                                                                |
+| -------------------------------------- | ---------------------------------- | ---------------- | ----------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------- |
+| `SourceControlHeaderContent.tsx:217`   | Unified / split selector           | keep with reason | Both options have visible translated labels and expose button semantics through `TabPill`.                  | None.                                                                                           |
+| `SessionReplay/index.tsx:269`          | Unified / split selector           | keep with reason | Both options have visible translated labels and expose button semantics through `TabPill`.                  | None.                                                                                           |
+| `GitCommitDetailContent/index.tsx:377` | Icon-only collapsed file-list rail | fix              | It has a tooltip title but no explicit accessible label.                                                    | Add the translated “show file list” string as `aria-label` in a coordinated rail-control sweep. |
+| `PrChangesTab.tsx:214`                 | Icon-only collapsed file-list rail | fix              | It has a tooltip title but no explicit accessible label.                                                    | Add the translated “show file list” string as `aria-label` in the same sweep.                   |
+| `DiffFileSection/index.tsx:418`        | Expandable file header             | keep with reason | The visible filename supplies an accessible name and `aria-expanded` communicates disclosure state.         | None.                                                                                           |
+| `FocusView.tsx:51`                     | No-file Focus empty state          | keep with reason | The translated caption explicitly tells the user to select a changed file and exposes no unrelated actions. | None.                                                                                           |
+
+## D5 — Duplication and abstraction candidates
+
+- **Abstract candidate:** the collapsed 24 px file-list rail appears in commit details, pull-request changes, and `GitFileDiffSplit`. A small shared rail-control component could centralize geometry, tooltip, and accessible naming. This is a multi-file sweep candidate and is intentionally not mixed into the diff-view consistency fix.
+- The new unified / split selectors intentionally reuse `TabPill` and one shared persisted atom; no new visual-pattern duplication was introduced.
+
+## Summary
+
+- **Fix candidates:** 3 (two rail-control accessible labels; one standardizable loading height)
+- **Keep with reason:** 12
+- **Abstract candidates:** 1
+- **Current change verdict:** the new controls follow the design system and introduce no new arbitrary colors, spacing, or inaccessible icon-only actions.
diff --git a/src/engines/GitWorkflow/GitHubDiff/types.ts b/src/engines/GitWorkflow/GitHubDiff/types.ts
index 52017e746..5c699e16a 100644
--- a/src/engines/GitWorkflow/GitHubDiff/types.ts
+++ b/src/engines/GitWorkflow/GitHubDiff/types.ts
@@ -3,6 +3,7 @@
  *
  * Type definitions for the diff viewer architecture.
  */
+import type { DiffViewMode } from "@src/types/git/types";
 
 // ============================================
 // Diff Line Types
@@ -98,7 +99,7 @@ export interface FileDiff {
 // ============================================
 
 /** The view mode for the diff */
-export type DiffViewMode = "unified" | "split";
+export type { DiffViewMode } from "@src/types/git/types";
 
 /** Expansion type for hunks */
 export type DiffHunkExpansionType = "up" | "down" | "short" | "full";
diff --git a/src/features/CodeMirror/Diff/index.tsx b/src/features/CodeMirror/Diff/index.tsx
index 626d57cc8..9d02fbd6e 100644
--- a/src/features/CodeMirror/Diff/index.tsx
+++ b/src/features/CodeMirror/Diff/index.tsx
@@ -31,6 +31,7 @@ import type { GitFileStatus } from "@src/config/gitStatus";
 import { createLogger } from "@src/hooks/logger";
 import { useEditorAppearanceSettings } from "@src/hooks/settings";
 import { EditorService } from "@src/services/workStation/EditorService";
+import type { DiffViewMode } from "@src/types/git/types";
 
 import { useSelectionExtension } from "../Editor/hooks/useSelectionExtension";
 import type { TextSelectionInfo } from "../Editor/types";
@@ -67,7 +68,7 @@ export interface CodeMirrorDiffProps {
   /** Container height */
   height?: string;
   /** Diff view mode: unified (inline) or split (side-by-side) */
-  viewMode?: "unified" | "split";
+  viewMode?: DiffViewMode;
   /** Read-only mode */
   readOnly?: boolean;
   /** Show merge controls (accept/reject buttons) */
diff --git a/src/features/CodeViewer/GitDiffViewer.tsx b/src/features/CodeViewer/GitDiffViewer.tsx
index d2f77b0f8..f95b651f0 100644
--- a/src/features/CodeViewer/GitDiffViewer.tsx
+++ b/src/features/CodeViewer/GitDiffViewer.tsx
@@ -7,6 +7,7 @@
 import React, { useState } from "react";
 
 import { Placeholder } from "@src/modules/shared/layouts/blocks";
+import type { DiffViewMode } from "@src/types/git/types";
 
 import { ModernSplitDiff } from "./ModernSplitDiff";
 import { VirtualizedModernDiff } from "./VirtualizedModernDiff";
@@ -15,7 +16,7 @@ import { VirtualizedModernDiff } from "./VirtualizedModernDiff";
 // Types
 // ============================================
 
-export type DiffViewMode = "unified" | "split";
+export type { DiffViewMode } from "@src/types/git/types";
 
 export interface GitDiffViewerProps {
   /** Original/old content */
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.test.ts b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.test.ts
new file mode 100644
index 000000000..34dfb6b28
--- /dev/null
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.test.ts
@@ -0,0 +1,82 @@
+import type { TFunction } from "i18next";
+import { createElement } from "react";
+import { renderToStaticMarkup } from "react-dom/server";
+import { describe, expect, it, vi } from "vitest";
+
+import type { WorkStationTab } from "@src/store/workstation/tabs";
+
+import { SourceControlHeaderContent } from "./SourceControlHeaderContent";
+
+vi.mock("@src/components/Button", () => ({
+  default: ({ title }: { title?: string }) =>
+    createElement("button", { "data-title": title }),
+}));
+
+vi.mock("@src/components/TabPill", () => ({
+  default: ({
+    activeTab,
+    tabs,
+  }: {
+    activeTab: string;
+    tabs: Array<{ key: string }>;
+  }) =>
+    createElement("div", {
+      "data-active-tab": activeTab,
+      "data-tabs": tabs.map((tab) => tab.key).join(","),
+    }),
+}));
+
+const t = ((key: string) => key) as TFunction;
+
+function sourceControlTab(mode: "focus" | "all-changes"): WorkStationTab {
+  return {
+    id: "source-control:changes",
+    type: "source-control",
+    title: "Review",
+    data: {
+      mode,
+      staged: false,
+      fileCount: 1,
+      focusPath: null,
+      historySelection: null,
+    },
+  } as WorkStationTab;
+}
+
+function renderHeader(mode: "focus" | "all-changes"): string {
+  return renderToStaticMarkup(
+    createElement(SourceControlHeaderContent, {
+      activeTab: sourceControlTab(mode),
+      sourceControlFilterMode: "uncommitted",
+      showSourceControlModePill: true,
+      gitReviewNavigationTotal: 0,
+      selectedIssue: null,
+      sourceControlRefreshSpinClass: undefined,
+      diffViewMode: "split",
+      t,
+      onDiffViewModeChange: vi.fn(),
+      onModeChange: vi.fn(),
+      onOpenHistoryInNewTab: vi.fn(),
+      onReviewPrevFile: vi.fn(),
+      onReviewNextFile: vi.fn(),
+      onCollapseAll: vi.fn(),
+      onRefresh: vi.fn(),
+    })
+  );
+}
+
+describe("SourceControlHeaderContent diff view controls", () => {
+  it("shows the shared unified/split control in All Changes", () => {
+    const markup = renderHeader("all-changes");
+
+    expect(markup).toContain('data-active-tab="split"');
+    expect(markup).toContain('data-tabs="unified,split"');
+  });
+
+  it("keeps the aggregate diff control out of Focus mode", () => {
+    const markup = renderHeader("focus");
+
+    expect(markup).not.toContain('data-tabs="unified,split"');
+    expect(markup).toContain('data-tabs="focus,all-changes"');
+  });
+});
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.tsx
index c1f2fb905..3fcce3b50 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/components/SourceControlHeaderContent.tsx
@@ -28,6 +28,7 @@ import type {
   SourceControlHistorySelection,
   WorkStationTab,
 } from "@src/store/workstation/tabs";
+import type { DiffViewMode } from "@src/types/git/types";
 
 export interface SourceControlHeaderContentProps {
   /** The active `source-control` tab (host guarantees the type). */
@@ -40,7 +41,9 @@ export interface SourceControlHeaderContentProps {
   sourceControlHeaderLeadingSlot?: ReactNode;
   sourceControlHeaderTrailingSlot?: ReactNode;
   sourceControlRefreshSpinClass: string | undefined;
+  diffViewMode: DiffViewMode;
   t: TFunction;
+  onDiffViewModeChange: (mode: DiffViewMode) => void;
   onModeChange: (mode: "focus" | "all-changes") => void;
   onOpenHistoryInNewTab: (selection: SourceControlHistorySelection) => void;
   onReviewPrevFile: () => void;
@@ -60,7 +63,9 @@ export const SourceControlHeaderContent: React.FC<
   sourceControlHeaderLeadingSlot,
   sourceControlHeaderTrailingSlot,
   sourceControlRefreshSpinClass,
+  diffViewMode,
   t,
+  onDiffViewModeChange,
   onModeChange,
   onOpenHistoryInNewTab,
   onReviewPrevFile,
@@ -197,16 +202,35 @@ export const SourceControlHeaderContent: React.FC<
         )}
 
         {showCollapseAll && (
-          <Button
-            htmlType="button"
-            variant="tertiary"
-            size="small"
-            iconOnly
-            className="flex-shrink-0"
-            onClick={onCollapseAll}
-            title={t("actions.collapseAll")}
-            icon={<ListChevronsDownUp size={HEADER_ICON_SIZE.md} />}
-          />
+          <>
+            <TabPill
+              activeTab={diffViewMode}
+              tabs={[
+                { key: "unified", label: t("workstation.unified") },
+                { key: "split", label: t("workstation.split") },
+              ]}
+              onChange={(key) => onDiffViewModeChange(key as DiffViewMode)}
+              variant="pill"
+              color="fill"
+              fillWidth={false}
+              size="small"
+            />
+            <span
+              className="mx-1.5 h-4 w-px shrink-0 bg-border-2"
+              role="separator"
+              aria-hidden
+            />
+            <Button
+              htmlType="button"
+              variant="tertiary"
+              size="small"
+              iconOnly
+              className="flex-shrink-0"
+              onClick={onCollapseAll}
+              title={t("actions.collapseAll")}
+              icon={<ListChevronsDownUp size={HEADER_ICON_SIZE.md} />}
+            />
+          </>
         )}
         <Button
           htmlType="button"
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitCommitDetailContent/index.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitCommitDetailContent/index.tsx
index 359601bf2..7637bdd7f 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitCommitDetailContent/index.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitCommitDetailContent/index.tsx
@@ -23,7 +23,6 @@ import { gitFetchStream } from "@src/api/http/git/streaming";
 import type { GitFileStatus } from "@src/config/gitStatus";
 import { CodeMirrorDiff } from "@src/features/CodeMirror";
 import {
-  type DiffViewMode,
   FileHeader,
   GIT_FILE_LIST_MAX_WIDTH,
   GIT_FILE_LIST_MIN_WIDTH,
@@ -38,6 +37,7 @@ import {
   editorWordWrapAtom,
 } from "@src/store/ui/editorSettingsAtom";
 import { activeStatusBarCallbacksAtom } from "@src/store/ui/workStationAtom";
+import { diffViewModeAtom } from "@src/store/workstation/codeEditor";
 import type { GitFile } from "@src/types/git/types";
 import { decodeOctalPath } from "@src/util/file/pathUtils";
 
@@ -76,7 +76,7 @@ const GitCommitDetailContent: React.FC<GitCommitDetailContentProps> = ({
   const { t } = useTranslation();
 
   const [fileListCollapsed, setFileListCollapsed] = useState(false);
-  const [viewMode, setViewMode] = useState<DiffViewMode>("unified");
+  const [viewMode, setViewMode] = useAtom(diffViewModeAtom);
   const [lineNumbers, setLineNumbers] = useAtom(editorLineNumbersAtom);
   const [wordWrap, setWordWrap] = useAtom(editorWordWrapAtom);
   const [highlightActiveLine, setHighlightActiveLine] = useAtom(
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitDiffContent/index.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitDiffContent/index.tsx
index 48f8d492a..9ea90d70e 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitDiffContent/index.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/GitDiffContent/index.tsx
@@ -32,11 +32,7 @@ import {
   hasConflictMarkers,
 } from "@src/features/CodeMirror";
 import { createLogger } from "@src/hooks/logger";
-import {
-  type DiffViewMode,
-  FileHeader,
-  FloatingBar,
-} from "@src/modules/WorkStation/shared";
+import { FileHeader, FloatingBar } from "@src/modules/WorkStation/shared";
 import { HUMANTOOLS_TEXT_KEYS } from "@src/modules/WorkStation/shared/textTokens";
 import { Placeholder } from "@src/modules/shared/layouts/blocks";
 import { EditorService } from "@src/services/workStation/EditorService";
@@ -48,6 +44,7 @@ import {
   editorLineNumbersAtom,
   editorWordWrapAtom,
 } from "@src/store/ui";
+import { diffViewModeAtom } from "@src/store/workstation/codeEditor";
 import type { GitFile } from "@src/types/git/types";
 import { isBinaryByExtension } from "@src/util/file/binaryDetection";
 import {
@@ -242,7 +239,7 @@ const GitDiffContentInner: React.FC<GitDiffContentProps> = ({
   });
 
   // View mode state for diff display
-  const [viewMode, setViewMode] = useState<DiffViewMode>("unified");
+  const [viewMode, setViewMode] = useAtom(diffViewModeAtom);
 
   // Local state for edited content
   const [editedContent, setEditedContent] = useState<string | null>(null);
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/AllChangesView.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/AllChangesView.tsx
index f33de7183..ebaf5d7e7 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/AllChangesView.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/AllChangesView.tsx
@@ -18,7 +18,10 @@ import React, {
 import { useTranslation } from "react-i18next";
 
 import { DiffSectionList } from "@src/modules/WorkStation/shared";
-import { sourceControlFocusTargetAtom } from "@src/store/workstation/codeEditor";
+import {
+  diffViewModeAtom,
+  sourceControlFocusTargetAtom,
+} from "@src/store/workstation/codeEditor";
 import type { GitFile } from "@src/types/git/types";
 
 import { useAllChangesFiles } from "./allChanges/useAllChangesFiles";
@@ -51,6 +54,7 @@ const AllChangesView: React.FC<AllChangesViewProps> = ({
 }) => {
   const { t } = useTranslation();
   const focusTarget = useAtomValue(sourceControlFocusTargetAtom);
+  const viewMode = useAtomValue(diffViewModeAtom);
 
   const {
     sortedFiles,
@@ -136,6 +140,7 @@ const AllChangesView: React.FC<AllChangesViewProps> = ({
   return (
     <DiffSectionList
       sections={sections}
+      viewMode={viewMode}
       loading={loading}
       emptyTitle={
         staged ? t("placeholders.noStagedChanges") : t("placeholders.noChanges")
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/FocusView.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/FocusView.tsx
index 4554d6c8c..e8febce6c 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/FocusView.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/FocusView.tsx
@@ -4,11 +4,9 @@
  * Single-file working-tree diff for the unified Source Control tab.
  */
 import React, { Suspense, memo } from "react";
+import { useTranslation } from "react-i18next";
 
-import {
-  NoTabsPlaceholder,
-  type QuickAction,
-} from "@src/modules/WorkStation/shared";
+import { NoTabsPlaceholder } from "@src/modules/WorkStation/shared";
 import { Placeholder } from "@src/modules/shared/layouts/blocks";
 import type { GitFile } from "@src/types/git/types";
 
@@ -37,8 +35,6 @@ export interface FocusViewProps {
   onUnsavedChange?: (hasUnsaved: boolean) => void;
   /** Render the file breadcrumb inside the main pane instead of the workstation header. */
   inlineFileHeader?: boolean;
-  /** Source Control navigation shown when no file is focused. */
-  emptyActions: QuickAction[];
 }
 
 const FocusView: React.FC<FocusViewProps> = ({
@@ -51,10 +47,13 @@ const FocusView: React.FC<FocusViewProps> = ({
   onClose,
   onUnsavedChange,
   inlineFileHeader = true,
-  emptyActions,
 }) => {
+  const { t } = useTranslation();
   const emptyPlaceholder = (
-    <NoTabsPlaceholder icon="source-control" actions={emptyActions} />
+    <NoTabsPlaceholder
+      icon="source-control"
+      caption={t("placeholders.selectFileToViewChanges")}
+    />
   );
 
   if (!hasFocus) {
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/index.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/index.tsx
index b14ba3121..94f9fadef 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/index.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainContent/index.tsx
@@ -206,7 +206,6 @@ const SourceControlMainContent: React.FC<SourceControlMainContentProps> = ({
           onFileSelect={onFileSelect}
           onClose={onCloseFocus}
           onUnsavedChange={onGitDiffUnsavedChange}
-          emptyActions={emptyFocusActions}
         />
       ) : (
         <AllChangesView
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainPane.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainPane.tsx
index 3ef40078f..fecc229ba 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainPane.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/SourceControlMainPane.tsx
@@ -41,6 +41,7 @@ export interface SourceControlMainPaneProps {
   gitFilesByPath: Map<string, GitFile>;
   sourceControlFiles: GitFile[];
   sourceControlFilterMode: string;
+  activeRepoRoot: string;
   gitDiffLoading: boolean;
   sourceControlCollapseAllSignal?: number;
   sourceControlQuickActions: QuickAction[];
@@ -57,6 +58,7 @@ const SourceControlMainPane: React.FC<SourceControlMainPaneProps> = ({
   gitFilesByPath,
   sourceControlFiles,
   sourceControlFilterMode,
+  activeRepoRoot,
   gitDiffLoading,
   sourceControlCollapseAllSignal,
   sourceControlQuickActions,
@@ -76,13 +78,14 @@ const SourceControlMainPane: React.FC<SourceControlMainPaneProps> = ({
     stateScopeKey: scopeKey,
   });
 
-  const { mode, staged, focusPath, historySelection, allFiles, focusGitFile } =
+  const { mode, staged, historySelection, allFiles, focusGitFile, hasFocus } =
     deriveSourceControlMainProps({
       tabData,
       gitFilesByPath,
       sourceControlFiles,
       sourceControlFilterMode,
       repoPath,
+      activeRepoRoot,
     });
 
   if (sourceControlFilterMode === "issues") {
@@ -127,7 +130,7 @@ const SourceControlMainPane: React.FC<SourceControlMainPaneProps> = ({
         <SourceControlMainContent
           mode={mode}
           focusGitFile={focusGitFile}
-          hasFocus={Boolean(focusPath)}
+          hasFocus={hasFocus}
           onForceReload={onForceReload}
           onFileSelect={onFileSelect}
           onCloseFocus={onCloseFocus}
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/FocusView.emptyState.test.ts b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/FocusView.emptyState.test.ts
new file mode 100644
index 000000000..8931cd5d4
--- /dev/null
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/FocusView.emptyState.test.ts
@@ -0,0 +1,44 @@
+import { createElement } from "react";
+import { renderToStaticMarkup } from "react-dom/server";
+import { describe, expect, it, vi } from "vitest";
+
+import FocusView from "../SourceControlMainContent/FocusView";
+
+vi.mock("react-i18next", () => ({
+  useTranslation: () => ({ t: (key: string) => key }),
+}));
+
+vi.mock("@src/modules/WorkStation/shared", () => ({
+  NoTabsPlaceholder: ({
+    caption,
+    actions,
+  }: {
+    caption?: string;
+    actions?: unknown[];
+  }) =>
+    createElement("div", {
+      "data-caption": caption,
+      "data-action-count": actions?.length ?? 0,
+    }),
+}));
+
+vi.mock("@src/modules/shared/layouts/blocks", () => ({
+  Placeholder: () => null,
+}));
+
+describe("FocusView empty state", () => {
+  it("asks the user to select a file instead of showing unrelated navigation", () => {
+    const markup = renderToStaticMarkup(
+      createElement(FocusView, {
+        gitFile: null,
+        loading: false,
+        hasFocus: false,
+      })
+    );
+
+    expect(markup).toContain(
+      'data-caption="placeholders.selectFileToViewChanges"'
+    );
+    expect(markup).toContain('data-action-count="0"');
+  });
+});
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/TEST_CASES.md b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/TEST_CASES.md
index f7abd5088..e388ed7d6 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/TEST_CASES.md
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/TEST_CASES.md
@@ -13,23 +13,26 @@ its diff view, scroll position, and lazy chunk survive navigation.
 
 ## Happy Path
 
-| #   | Steps                                                                                                                  | Expected Result                                                                                                           |
-| --- | ---------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------- |
-| 1   | Open Source Control tab, select a file in Focus mode, scroll the diff. Open a file tab, then return to Source Control. | Same focused diff is shown at the same scroll position; no loading flash (lazy chunk not re-imported).                    |
-| 2   | Open Source Control → All Changes, scroll partway down the list. Switch to a file tab and back.                        | All Changes list is preserved at the same scroll offset.                                                                  |
-| 3   | Never open Source Control during a session.                                                                            | The Source Control main pane chunk is not mounted/parsed (lazy — only mounts after first visit).                          |
-| 4   | Open Source Control Focus mode without selecting a file.                                                               | A Git-branch placeholder offers View Issues, View Git history, and View PRs; each action opens the matching sidebar mode. |
-| 5   | Open an empty History, Issues, or PR detail state.                                                                     | The current destination is omitted; View Source Control appears first, followed by the other destinations.                |
+| #   | Steps                                                                                                                  | Expected Result                                                                                                 |
+| --- | ---------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------- |
+| 1   | Open Source Control tab, select a file in Focus mode, scroll the diff. Open a file tab, then return to Source Control. | Same focused diff is shown at the same scroll position; no loading flash (lazy chunk not re-imported).          |
+| 2   | Open Source Control → All Changes, scroll partway down the list. Switch to a file tab and back.                        | All Changes list is preserved at the same scroll offset.                                                        |
+| 3   | Never open Source Control during a session.                                                                            | The Source Control main pane chunk is not mounted/parsed (lazy — only mounts after first visit).                |
+| 4   | Open Source Control Focus mode without selecting a file.                                                               | A Git-branch placeholder asks the user to select a changed file and does not show unrelated navigation actions. |
+| 5   | Open an empty History, Issues, or PR detail state.                                                                     | The current destination is omitted; View Source Control appears first, followed by the other destinations.      |
+| 6   | Select Split in All Changes, then open Focus, a commit, or PR Changes.                                                 | Every text diff uses Split until the user switches back to Unified, including after remount/reload.             |
 
 ## Edge Cases
 
-| #   | Scenario                   | Steps                                                                                                    | Expected Result                                                                                          |
-| --- | -------------------------- | -------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------- |
-| 1   | Empty working tree         | Open Source Control with no changes.                                                                     | Empty placeholder shown; switching away/back keeps it stable.                                            |
-| 2   | Filter change while hidden | On Source Control, set filter to Staged. Switch to a file tab; stage a file via another surface; return. | Returning shows the staged-filtered list with the staged file (data stayed populated while hidden).      |
-| 3   | Terminal active            | Open a terminal tab while Source Control was previously visited.                                         | Source Control overlay is hidden (pointer-events none, aria-hidden); terminal renders normally.          |
-| 4   | Rapid tab switching        | Quickly toggle between a file tab and Source Control several times.                                      | No flash/remount; diff + scroll remain stable each return.                                               |
-| 5   | Repo switch                | Switch repos while Source Control is the active tab.                                                     | Pane updates to the new repo's status (focus target cleared by existing `useSourceControlSetup` effect). |
+| #   | Scenario                   | Steps                                                                                                    | Expected Result                                                                                                   |
+| --- | -------------------------- | -------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------- |
+| 1   | Empty working tree         | Open Source Control with no changes.                                                                     | Empty placeholder shown; switching away/back keeps it stable.                                                     |
+| 2   | Filter change while hidden | On Source Control, set filter to Staged. Switch to a file tab; stage a file via another surface; return. | Returning shows the staged-filtered list with the staged file (data stayed populated while hidden).               |
+| 3   | Terminal active            | Open a terminal tab while Source Control was previously visited.                                         | Source Control overlay is hidden (pointer-events none, aria-hidden); terminal renders normally.                   |
+| 4   | Rapid tab switching        | Quickly toggle between a file tab and Source Control several times.                                      | No flash/remount; diff + scroll remain stable each return.                                                        |
+| 5   | Repo switch                | Switch repos while Source Control is the active tab.                                                     | Pane updates to the new repo's status (focus target cleared by existing `useSourceControlSetup` effect).          |
+| 6   | Worktree scope switch      | Focus a host-repo file, then switch the scope picker to a linked worktree.                               | The host file is no longer rendered; All Changes contains only files whose `repoRoot` matches the worktree.       |
+| 7   | Filter invalidates focus   | Focus an unstaged file, then switch the Source Control filter to Staged.                                 | The stale unstaged file is not rendered; Focus shows the select-file placeholder until a staged file is selected. |
 
 ## Error / Degraded States
 
@@ -50,6 +53,8 @@ its diff view, scroll position, and lazy chunk survive navigation.
 - [ ] Users who never open Source Control do not pay the heavy chunk's mount cost.
 - [ ] `TabContentRenderer` no longer double-renders the `source-control` case (it is a no-op; the overlay owns rendering).
 - [ ] Empty Source Control detail states use Source Control navigation rather than editor/workspace actions.
+- [ ] Focus and All Changes never render files outside the active repo/worktree scope or staged/unstaged filter.
+- [ ] All Changes exposes the shared Unified/Split control; the selected mode is reused by Focus, commit, PR, and replay diffs.
 - [ ] No new TypeScript errors; no new lint warnings; `deriveSourceControlMainProps` / `getGitFileForPath` unit tests pass.
 
 ## Notes / Manual QA required
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/sourceControlMainProps.test.ts b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/sourceControlMainProps.test.ts
index 72e44aa0e..1219d1ccd 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/sourceControlMainProps.test.ts
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/__tests__/sourceControlMainProps.test.ts
@@ -26,6 +26,7 @@ function createInput(
     sourceControlFiles: [],
     sourceControlFilterMode: "uncommitted",
     repoPath: "/repo",
+    activeRepoRoot: "/repo",
     ...overrides,
   };
 }
@@ -129,6 +130,19 @@ describe("deriveSourceControlMainProps", () => {
     expect(result.allFiles).toEqual([s1, s2]);
   });
 
+  it("isolates All Changes to the active repo or worktree scope", () => {
+    const host = createGitFile({ path: "host.ts", repoRoot: "/repo" });
+    const worktree = createGitFile({ path: "wt.ts", repoRoot: "/wt" });
+    const result = deriveSourceControlMainProps(
+      createInput({
+        sourceControlFiles: [host, worktree],
+        activeRepoRoot: "/wt",
+      })
+    );
+
+    expect(result.allFiles).toEqual([worktree]);
+  });
+
   it("resolves the focus git file for the focus path", () => {
     const file = createGitFile({ path: "src/a.ts" });
     const result = deriveSourceControlMainProps(
@@ -140,4 +154,44 @@ describe("deriveSourceControlMainProps", () => {
     expect(result.hasFocus).toBe(true);
     expect(result.focusGitFile).toBe(file);
   });
+
+  it("does not render a remembered focus file from another scope", () => {
+    const host = createGitFile({ path: "src/a.ts", repoRoot: "/repo" });
+    const result = deriveSourceControlMainProps(
+      createInput({
+        tabData: { focusPath: "/repo/src/a.ts" },
+        gitFilesByPath: new Map([[host.path, host]]),
+        activeRepoRoot: "/wt",
+      })
+    );
+
+    expect(result.hasFocus).toBe(false);
+    expect(result.focusGitFile).toBeNull();
+  });
+
+  it("does not render a focus file excluded by the active staged filter", () => {
+    const unstaged = createGitFile({ path: "src/a.ts", staged: false });
+    const result = deriveSourceControlMainProps(
+      createInput({
+        tabData: { focusPath: "/repo/src/a.ts" },
+        gitFilesByPath: new Map([[unstaged.path, unstaged]]),
+        sourceControlFilterMode: "staged",
+      })
+    );
+
+    expect(result.hasFocus).toBe(false);
+    expect(result.focusGitFile).toBeNull();
+  });
+
+  it("keeps an in-scope focus path pending while its file is loading", () => {
+    const result = deriveSourceControlMainProps(
+      createInput({
+        tabData: { focusPath: "/wt/src/a.ts" },
+        activeRepoRoot: "/wt",
+      })
+    );
+
+    expect(result.hasFocus).toBe(true);
+    expect(result.focusGitFile).toBeNull();
+  });
 });
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/sourceControlMainProps.ts b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/sourceControlMainProps.ts
index 8b6170ced..c519a2baf 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/sourceControlMainProps.ts
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/content/sourceControlMainProps.ts
@@ -61,6 +61,8 @@ export interface DeriveSourceControlMainPropsInput {
   /** "uncommitted" | "staged" | "unstaged" | "history" | ... */
   sourceControlFilterMode: string;
   repoPath: string;
+  /** Repo/worktree root selected by the Source Control scope picker. */
+  activeRepoRoot: string;
 }
 
 export interface SourceControlMainDerivedProps {
@@ -73,6 +75,51 @@ export interface SourceControlMainDerivedProps {
   hasFocus: boolean;
 }
 
+function normalizeRepoPath(path: string): string {
+  return path.replace(/\\/g, "/").replace(/\/+$/, "");
+}
+
+function isPathInRepoScope(
+  filePath: string,
+  repoPath: string,
+  activeRepoRoot: string
+): boolean {
+  const normalizedPath = normalizeRepoPath(filePath);
+  const normalizedRepoPath = normalizeRepoPath(repoPath);
+  const normalizedActiveRoot = normalizeRepoPath(activeRepoRoot);
+  const isAbsolute =
+    normalizedPath.startsWith("/") || /^[A-Za-z]:\//.test(normalizedPath);
+
+  if (!isAbsolute) {
+    return normalizedActiveRoot === normalizedRepoPath;
+  }
+
+  return (
+    normalizedPath === normalizedActiveRoot ||
+    normalizedPath.startsWith(`${normalizedActiveRoot}/`)
+  );
+}
+
+function isFileInRepoScope(
+  file: GitFile,
+  repoPath: string,
+  activeRepoRoot: string
+): boolean {
+  return (
+    normalizeRepoPath(file.repoRoot ?? repoPath) ===
+    normalizeRepoPath(activeRepoRoot)
+  );
+}
+
+function matchesSourceControlFilter(
+  file: GitFile,
+  sourceControlFilterMode: string
+): boolean {
+  if (sourceControlFilterMode === "staged") return file.staged;
+  if (sourceControlFilterMode === "unstaged") return !file.staged;
+  return true;
+}
+
 /**
  * Derive every prop `SourceControlMainContent` needs from a Source Control tab
  * payload plus the current working-tree status / filters. Pure; no React.
@@ -83,6 +130,7 @@ export function deriveSourceControlMainProps({
   sourceControlFiles,
   sourceControlFilterMode,
   repoPath,
+  activeRepoRoot,
 }: DeriveSourceControlMainPropsInput): SourceControlMainDerivedProps {
   const focusPath = tabData.focusPath ?? null;
   const mode: SourceControlPillMode =
@@ -99,15 +147,27 @@ export function deriveSourceControlMainProps({
         ? gitStatusFiles
         : embeddedFiles;
 
-  const allFiles = unfilteredFiles.filter((file) => {
-    if (sourceControlFilterMode === "staged" && !file.staged) return false;
-    if (sourceControlFilterMode === "unstaged" && file.staged) return false;
-    return true;
-  });
+  const allFiles = unfilteredFiles.filter(
+    (file) =>
+      isFileInRepoScope(file, repoPath, activeRepoRoot) &&
+      matchesSourceControlFilter(file, sourceControlFilterMode)
+  );
 
-  const focusGitFile = focusPath
+  const resolvedFocusFile = focusPath
     ? (getGitFileForPath(focusPath, repoPath, gitFilesByPath) ?? null)
     : null;
+  const focusPathInActiveScope = focusPath
+    ? isPathInRepoScope(focusPath, repoPath, activeRepoRoot)
+    : false;
+  const focusGitFile =
+    resolvedFocusFile &&
+    isFileInRepoScope(resolvedFocusFile, repoPath, activeRepoRoot) &&
+    matchesSourceControlFilter(resolvedFocusFile, sourceControlFilterMode)
+      ? resolvedFocusFile
+      : null;
+  const hasFocus = Boolean(
+    focusPath && focusPathInActiveScope && (!resolvedFocusFile || focusGitFile)
+  );
 
   return {
     mode,
@@ -116,6 +176,6 @@ export function deriveSourceControlMainProps({
     historySelection,
     allFiles,
     focusGitFile,
-    hasFocus: Boolean(focusPath),
+    hasFocus,
   };
 }
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/hooks/useSourceControlPaneActions.ts b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/hooks/useSourceControlPaneActions.ts
index 6aa2c15df..1cae2467b 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/hooks/useSourceControlPaneActions.ts
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/hooks/useSourceControlPaneActions.ts
@@ -29,6 +29,10 @@ import {
   createStashDetailTab,
 } from "@src/store/workstation/tabs";
 
+import {
+  type SourceControlMainMode,
+  setSourceControlMainMode,
+} from "../../../sourceControlStateTransitions";
 import {
   type SourceControlDestination,
   createSourceControlQuickActions,
@@ -51,7 +55,7 @@ export interface UseSourceControlPaneActionsReturn {
   handleSourceControlRefresh: () => void;
   /** Monotonic counter — bumping it tells All Changes to collapse every group */
   sourceControlCollapseAllSignal: number;
-  handleSourceControlModeChange: (mode: "focus" | "all-changes") => void;
+  handleSourceControlModeChange: (mode: SourceControlMainMode) => void;
   handleSourceControlCollapseAll: () => void;
   handleSourceControlCloseFocus: () => void;
   /** Current review-sequence snapshot (`{ current, total }`) */
@@ -94,28 +98,8 @@ export function useSourceControlPaneActions({
     useState(0);
 
   const handleSourceControlModeChange = useCallback(
-    (mode: "focus" | "all-changes") => {
-      updatePaneState((state) => {
-        const tabIndex = state.tabs.findIndex(
-          (item) => item.type === "source-control"
-        );
-        if (tabIndex === -1) return state;
-        const existing = state.tabs[tabIndex];
-        if (existing.data.mode === mode && !existing.data.historySelection) {
-          return state;
-        }
-        const nextTabs = [...state.tabs];
-        nextTabs[tabIndex] = {
-          ...existing,
-          data: {
-            ...existing.data,
-            mode,
-            historySelection: null,
-          },
-        };
-        return { ...state, tabs: nextTabs };
-      });
-    },
+    (mode: SourceControlMainMode) =>
+      updatePaneState((state) => setSourceControlMainMode(state, mode)),
     [updatePaneState]
   );
 
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/index.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/index.tsx
index aff103ac1..70cf15b67 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/index.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/index.tsx
@@ -20,7 +20,7 @@
  * - types.ts     - TypeScript types
  * - config.ts    - Constants and configuration
  */
-import { useAtomValue } from "jotai";
+import { useAtom, useAtomValue } from "jotai";
 import React, {
   Suspense,
   memo,
@@ -42,6 +42,7 @@ import UnifiedTabContent from "@src/modules/WorkStation/TabContent/UnifiedTabCon
 import { NoTabsPlaceholder } from "@src/modules/WorkStation/shared";
 import { Placeholder } from "@src/modules/shared/layouts/blocks";
 import { workStationPrimarySidebarCollapsedAtom } from "@src/store/ui/workStationAtom";
+import { diffViewModeAtom } from "@src/store/workstation/codeEditor";
 import { workstationSelectedIssueAtomFamily } from "@src/store/workstation/codeEditor/workstationIssueAtom";
 import { workstationRepoScopeKey } from "@src/store/workstation/codeEditor/workstationPrAtom";
 import type { GitFile } from "@src/types/git/types";
@@ -103,6 +104,7 @@ const EditorContent: React.FC<EditorContentProps> = memo(
     sourceControlHeaderLeadingSlot,
     sourceControlHeaderTrailingSlot,
     sourceControlFilterMode = "uncommitted",
+    sourceControlActiveRepoRoot = repoPath,
     showSourceControlModePill = true,
   }) => {
     // ============================================
@@ -116,6 +118,7 @@ const EditorContent: React.FC<EditorContentProps> = memo(
     const selectedIssueState = useAtomValue(
       workstationSelectedIssueAtomFamily(scopeKey)
     );
+    const [diffViewMode, setDiffViewMode] = useAtom(diffViewModeAtom);
 
     // ============================================
     // Pane State Management (extracted hook)
@@ -281,7 +284,9 @@ const EditorContent: React.FC<EditorContentProps> = memo(
           sourceControlHeaderLeadingSlot={sourceControlHeaderLeadingSlot}
           sourceControlHeaderTrailingSlot={sourceControlHeaderTrailingSlot}
           sourceControlRefreshSpinClass={sourceControlRefreshSpinClass}
+          diffViewMode={diffViewMode}
           t={t}
+          onDiffViewModeChange={setDiffViewMode}
           onModeChange={handleSourceControlModeChange}
           onOpenHistoryInNewTab={handleOpenSourceControlHistoryInNewTab}
           onReviewPrevFile={handleReviewPrevFile}
@@ -292,6 +297,7 @@ const EditorContent: React.FC<EditorContentProps> = memo(
       );
     }, [
       activeTab,
+      diffViewMode,
       gitReviewNavigation.total,
       handleOpenSourceControlHistoryInNewTab,
       handleReviewNextFile,
@@ -305,6 +311,7 @@ const EditorContent: React.FC<EditorContentProps> = memo(
       sourceControlHeaderLeadingSlot,
       sourceControlHeaderTrailingSlot,
       sourceControlRefreshSpinClass,
+      setDiffViewMode,
       t,
     ]);
 
@@ -464,6 +471,7 @@ const EditorContent: React.FC<EditorContentProps> = memo(
                     gitFilesByPath={gitFilesByPath}
                     sourceControlFiles={sourceControlBaseFiles}
                     sourceControlFilterMode={sourceControlFilterMode}
+                    activeRepoRoot={sourceControlActiveRepoRoot}
                     gitDiffLoading={gitDiffLoading}
                     sourceControlCollapseAllSignal={
                       sourceControlCollapseAllSignal
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/types.ts b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/types.ts
index ed34bd0b0..7fe917dd4 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/types.ts
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorMainPane/types.ts
@@ -78,6 +78,8 @@ export interface EditorContentProps {
   sourceControlHeaderLeadingSlot?: ReactNode;
   sourceControlHeaderTrailingSlot?: ReactNode;
   sourceControlFilterMode?: SourceControlFilterMode;
+  /** Repo/worktree root selected by the Source Control scope picker. */
+  sourceControlActiveRepoRoot?: string;
   showSourceControlModePill?: boolean;
 }
 
diff --git a/src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrChangesTab.tsx b/src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrChangesTab.tsx
index 4c0b221ed..3579179cb 100644
--- a/src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrChangesTab.tsx
+++ b/src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrChangesTab.tsx
@@ -17,7 +17,6 @@ import type { GitHubReviewComment, PrFile } from "@src/api/tauri/github";
 import type { GitFileStatus } from "@src/config/gitStatus";
 import { CodeMirrorDiff } from "@src/features/CodeMirror";
 import {
-  type DiffViewMode,
   FileHeader,
   GIT_FILE_LIST_MAX_WIDTH,
   GIT_FILE_LIST_MIN_WIDTH,
@@ -32,6 +31,7 @@ import {
   editorWordWrapAtom,
 } from "@src/store/ui/editorSettingsAtom";
 import { activeStatusBarCallbacksAtom } from "@src/store/ui/workStationAtom";
+import { diffViewModeAtom } from "@src/store/workstation/codeEditor";
 import type { GitFile } from "@src/types/git/types";
 
 import { PrReviewThreadsPanel } from "./PrReviewThreadsPanel";
@@ -92,7 +92,7 @@ export const PrChangesTab: React.FC<PrChangesTabProps> = ({
   const { t } = useTranslation("common");
 
   const [fileListCollapsed, setFileListCollapsed] = useState(false);
-  const [viewMode, setViewMode] = useState<DiffViewMode>("unified");
+  const [viewMode, setViewMode] = useAtom(diffViewModeAtom);
   const [lineNumbers, setLineNumbers] = useAtom(editorLineNumbersAtom);
   const [wordWrap, setWordWrap] = useAtom(editorWordWrapAtom);
   const [highlightActiveLine, setHighlightActiveLine] = useAtom(
diff --git a/src/modules/WorkStation/CodeEditor/__tests__/TEST_CASES.md b/src/modules/WorkStation/CodeEditor/__tests__/TEST_CASES.md
index fa9d5ace9..5f697be57 100644
--- a/src/modules/WorkStation/CodeEditor/__tests__/TEST_CASES.md
+++ b/src/modules/WorkStation/CodeEditor/__tests__/TEST_CASES.md
@@ -12,9 +12,10 @@ resolver it now delegates to (`resolveGitDiffSelection`).
 
 | #   | Steps                                                                   | Expected Result                                                                                                                                                                  |
 | --- | ----------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| 1   | In Source Control "all changes" view, click a changed file              | Diff opens in focus target; `resolveGitDiffSelection` returns `isAllChangesView: true`, correct absolute + relative paths                                                        |
-| 2   | In Source Control focus/non-all-changes view, click a file              | Falls through to `handleGitFileSelect` (unified focus tab)                                                                                                                       |
-| 3   | Navigate between editor tabs repeatedly while Source Control stays warm | The warm Source Control tree does NOT re-render; `SidebarSlot` context identity stays stable because `handleDiffSidebarFileSelect` identity is stable across `activeTab` changes |
+| 1   | In Source Control "all changes" view, click a changed file              | Matching section opens and scrolls into view; the absolute path is remembered without leaving All Changes                                                                        |
+| 2   | Switch from All Changes to Focus after step 1                           | The remembered file opens as a single-file diff and exposes the unified / split toggle                                                                                           |
+| 3   | In Source Control focus/non-all-changes view, click a file              | Falls through to `handleGitFileSelect` and replaces the focused file                                                                                                             |
+| 4   | Navigate between editor tabs repeatedly while Source Control stays warm | The warm Source Control tree does NOT re-render; `SidebarSlot` context identity stays stable because `handleDiffSidebarFileSelect` identity is stable across `activeTab` changes |
 
 ## Edge Cases
 
@@ -24,6 +25,8 @@ resolver it now delegates to (`resolveGitDiffSelection`).
 | 2   | Already-absolute path     | File path begins with `/` and host repo prefix           | `absolutePath` unchanged, `relativePath` stripped of repo prefix                               |
 | 3   | Null/undefined active tab | Resolve with no active tab                               | `isAllChangesView` is `false` (routes to focus select)                                         |
 | 4   | Rapid navigation          | Switch tabs many times quickly                           | Callback identity unchanged each render (refs hold latest `activeTab` / `handleGitFileSelect`) |
+| 5   | Rapid file selection      | Click multiple All Changes files, then switch to Focus   | The most recently clicked file opens                                                           |
+| 6   | No previous selection     | Enter Focus before clicking any changed file             | Shows “Select a file to view changes”; no Issues / history / PR shortcuts                      |
 
 ## Error / Degraded States
 
@@ -41,6 +44,8 @@ resolver it now delegates to (`resolveGitDiffSelection`).
 - [x] `handleDiffSidebarFileSelect` no longer lists `activeTab` in its `useCallback` deps; reads it via `activeTabRef`.
 - [x] `handleGitFileSelect` (unstable — closes over per-render `gitDiffState`) read via `handleGitFileSelectRef`.
 - [x] `gitDiffState.setFile` destructured (stable) instead of depending on the whole `gitDiffState` object.
+- [x] All Changes selection persists `focusPath` without switching modes; Focus reuses it.
+- [x] The no-selection Focus render gate has a regression test for its explicit empty state.
 - [x] No new TypeScript / lint errors in touched files.
 
 ## Notes
diff --git a/src/modules/WorkStation/CodeEditor/__tests__/sourceControlStateTransitions.test.ts b/src/modules/WorkStation/CodeEditor/__tests__/sourceControlStateTransitions.test.ts
new file mode 100644
index 000000000..d9dc3dc6c
--- /dev/null
+++ b/src/modules/WorkStation/CodeEditor/__tests__/sourceControlStateTransitions.test.ts
@@ -0,0 +1,136 @@
+import { describe, expect, it } from "vitest";
+
+import type { PanelState, WorkStationTab } from "@src/store/workstation/tabs";
+import type { GitFile } from "@src/types/git/types";
+
+import { deriveSourceControlMainProps } from "../Panels/EditorMainPane/content/sourceControlMainProps";
+import {
+  rememberSourceControlFocusPath,
+  setSourceControlMainMode,
+} from "../sourceControlStateTransitions";
+
+function sourceControlTab(data: Record<string, unknown> = {}): WorkStationTab {
+  return {
+    id: "source-control",
+    type: "source-control",
+    title: "Source Control",
+    data,
+  } as WorkStationTab;
+}
+
+function fileTab(): WorkStationTab {
+  return {
+    id: "file:/repo/README.md",
+    type: "file",
+    title: "README.md",
+    data: { path: "/repo/README.md" },
+  } as WorkStationTab;
+}
+
+function panel(data: Record<string, unknown> = {}): PanelState {
+  return {
+    tabs: [fileTab(), sourceControlTab(data)],
+    activeTabId: "source-control",
+  };
+}
+
+function changedFile(path = "src/a.ts"): GitFile {
+  return {
+    id: `${path}-0`,
+    path,
+    status: "modified",
+    staged: false,
+    additions: 1,
+    deletions: 0,
+    original_path: null,
+  };
+}
+
+describe("Source Control Focus hand-off", () => {
+  it("opens the last file inspected in All Changes when Focus is selected", () => {
+    const file = changedFile();
+    const allChangesState = panel({ mode: "all-changes", focusPath: null });
+
+    const remembered = rememberSourceControlFocusPath(
+      allChangesState,
+      "/repo/src/a.ts"
+    );
+    const rememberedTab = remembered.tabs.find(
+      (tab) => tab.type === "source-control"
+    );
+    expect(rememberedTab?.data).toMatchObject({
+      mode: "all-changes",
+      focusPath: "/repo/src/a.ts",
+    });
+
+    const focused = setSourceControlMainMode(remembered, "focus");
+    const focusedTab = focused.tabs.find(
+      (tab) => tab.type === "source-control"
+    );
+    const view = deriveSourceControlMainProps({
+      tabData: focusedTab?.data ?? {},
+      gitFilesByPath: new Map([[file.path, file]]),
+      sourceControlFiles: [file],
+      sourceControlFilterMode: "uncommitted",
+      repoPath: "/repo",
+      activeRepoRoot: "/repo",
+    });
+
+    expect(view.mode).toBe("focus");
+    expect(view.hasFocus).toBe(true);
+    expect(view.focusGitFile).toBe(file);
+  });
+
+  it("uses the latest file after repeated All Changes selections", () => {
+    const first = rememberSourceControlFocusPath(
+      panel({ mode: "all-changes" }),
+      "/repo/src/a.ts"
+    );
+    const latest = rememberSourceControlFocusPath(first, "/repo/src/b.ts");
+    const sourceControl = latest.tabs.find(
+      (tab) => tab.type === "source-control"
+    );
+
+    expect(sourceControl?.data.focusPath).toBe("/repo/src/b.ts");
+    expect(sourceControl?.data.mode).toBe("all-changes");
+  });
+
+  it("retains the remembered file across mode switches and clears history detail", () => {
+    const initial = panel({
+      mode: "all-changes",
+      focusPath: "/repo/src/a.ts",
+      historySelection: { type: "commit", commitSha: "abc" },
+    });
+
+    const focused = setSourceControlMainMode(initial, "focus");
+    const allChanges = setSourceControlMainMode(focused, "all-changes");
+    const sourceControl = allChanges.tabs.find(
+      (tab) => tab.type === "source-control"
+    );
+
+    expect(sourceControl?.data).toMatchObject({
+      mode: "all-changes",
+      focusPath: "/repo/src/a.ts",
+      historySelection: null,
+    });
+  });
+
+  it("does not alter unrelated tabs or panels without Source Control", () => {
+    const initial = panel({ mode: "all-changes" });
+    const unrelatedTab = initial.tabs[0];
+    const updated = rememberSourceControlFocusPath(initial, "/repo/src/a.ts");
+    expect(updated.tabs[0]).toBe(unrelatedTab);
+    expect(updated.activeTabId).toBe(initial.activeTabId);
+
+    const withoutSourceControl: PanelState = {
+      tabs: [fileTab()],
+      activeTabId: "file:/repo/README.md",
+    };
+    expect(
+      rememberSourceControlFocusPath(withoutSourceControl, "/repo/src/a.ts")
+    ).toBe(withoutSourceControl);
+    expect(setSourceControlMainMode(withoutSourceControl, "focus")).toBe(
+      withoutSourceControl
+    );
+  });
+});
diff --git a/src/modules/WorkStation/CodeEditor/index.tsx b/src/modules/WorkStation/CodeEditor/index.tsx
index 135a2fc6f..6da45f65d 100644
--- a/src/modules/WorkStation/CodeEditor/index.tsx
+++ b/src/modules/WorkStation/CodeEditor/index.tsx
@@ -205,6 +205,7 @@ export const CodeEditor: React.FC<CodeEditorProps> = memo(
     const {
       sourceControlFilterMode,
       sourceControlFilterCounts,
+      sourceControlActiveRepoRoot,
       sourceControlHeaderFilter,
       sourceControlHeaderScopePicker,
       tabSidebarExtraContext,
@@ -449,6 +450,7 @@ export const CodeEditor: React.FC<CodeEditorProps> = memo(
             sourceControlHeaderLeadingSlot={editorSourceControlScopePicker}
             sourceControlHeaderTrailingSlot={editorSourceControlHeaderSlot}
             sourceControlFilterMode={editorSourceControlFilterMode}
+            sourceControlActiveRepoRoot={sourceControlActiveRepoRoot}
             showSourceControlModePill={editorShowSourceControlModePill}
           />
         </div>
@@ -479,6 +481,7 @@ export const CodeEditor: React.FC<CodeEditorProps> = memo(
         editorSourceControlScopePicker,
         editorSourceControlHeaderSlot,
         editorSourceControlFilterMode,
+        sourceControlActiveRepoRoot,
         editorShowSourceControlModePill,
       ]
     );
diff --git a/src/modules/WorkStation/CodeEditor/sourceControlStateTransitions.ts b/src/modules/WorkStation/CodeEditor/sourceControlStateTransitions.ts
new file mode 100644
index 000000000..2d7224374
--- /dev/null
+++ b/src/modules/WorkStation/CodeEditor/sourceControlStateTransitions.ts
@@ -0,0 +1,63 @@
+import type { PanelState } from "@src/store/workstation/tabs";
+
+export type SourceControlMainMode = "focus" | "all-changes";
+
+/**
+ * Remember the last changed file the user inspected without leaving the current
+ * Source Control mode. All Changes uses this as the hand-off target when the
+ * user later switches to Focus.
+ */
+export function rememberSourceControlFocusPath(
+  state: PanelState,
+  focusPath: string
+): PanelState {
+  const tabIndex = state.tabs.findIndex(
+    (item) => item.type === "source-control"
+  );
+  if (tabIndex === -1) return state;
+
+  const existing = state.tabs[tabIndex];
+  if (existing.data.focusPath === focusPath) return state;
+
+  const nextTabs = [...state.tabs];
+  nextTabs[tabIndex] = {
+    ...existing,
+    data: {
+      ...existing.data,
+      focusPath,
+    },
+  };
+
+  return { ...state, tabs: nextTabs };
+}
+
+/**
+ * Switch the Source Control main surface while retaining its remembered file.
+ * History detail is mutually exclusive with the Focus / All Changes surfaces.
+ */
+export function setSourceControlMainMode(
+  state: PanelState,
+  mode: SourceControlMainMode
+): PanelState {
+  const tabIndex = state.tabs.findIndex(
+    (item) => item.type === "source-control"
+  );
+  if (tabIndex === -1) return state;
+
+  const existing = state.tabs[tabIndex];
+  if (existing.data.mode === mode && !existing.data.historySelection) {
+    return state;
+  }
+
+  const nextTabs = [...state.tabs];
+  nextTabs[tabIndex] = {
+    ...existing,
+    data: {
+      ...existing.data,
+      mode,
+      historySelection: null,
+    },
+  };
+
+  return { ...state, tabs: nextTabs };
+}
diff --git a/src/modules/WorkStation/CodeEditor/useSourceControlSetup.ts b/src/modules/WorkStation/CodeEditor/useSourceControlSetup.ts
index a560f95e0..e35217d0b 100644
--- a/src/modules/WorkStation/CodeEditor/useSourceControlSetup.ts
+++ b/src/modules/WorkStation/CodeEditor/useSourceControlSetup.ts
@@ -38,6 +38,7 @@ import {
   resolveScopeRepoRoot,
 } from "./Panels/EditorPrimarySidebar/tabs/sourceControlScopePickerHelpers";
 import { resolveGitDiffSelection } from "./sourceControlSelection";
+import { rememberSourceControlFocusPath } from "./sourceControlStateTransitions";
 import { useStashCount } from "./useStashCount";
 
 interface UseSourceControlSetupParams {
@@ -53,6 +54,8 @@ interface UseSourceControlSetupParams {
 export interface UseSourceControlSetupReturn {
   sourceControlFilterMode: SourceControlFilterMode;
   sourceControlFilterCounts: SourceControlFilterCounts;
+  /** Repo/worktree root currently selected by the Source Control scope picker. */
+  sourceControlActiveRepoRoot: string;
   sourceControlHeaderFilter: React.ReactNode;
   sourceControlHeaderScopePicker: React.ReactNode;
   tabSidebarExtraContext: {
@@ -106,6 +109,10 @@ export function useSourceControlSetup({
     enabled: isGitInitialized === true && hasWorktrees,
     worktreesReady: !worktreesLoading,
   });
+  const sourceControlActiveRepoRoot = useMemo(
+    () => resolveScopeRepoRoot(scope, repoPath),
+    [repoPath, scope]
+  );
 
   const repoName = useMemo(() => {
     const segments = repoPath.replace(/\/+$/, "").split("/");
@@ -150,9 +157,8 @@ export function useSourceControlSetup({
     if (!repoPath) {
       return { uncommitted: 0, unstaged: 0, staged: 0 };
     }
-    const activeRepoRoot = resolveScopeRepoRoot(scope, repoPath);
     const files = Array.from(gitFilesByPath.values()).filter(
-      (file) => (file.repoRoot ?? repoPath) === activeRepoRoot
+      (file) => (file.repoRoot ?? repoPath) === sourceControlActiveRepoRoot
     );
     const staged = files.filter((file) => file.staged).length;
     return {
@@ -160,7 +166,7 @@ export function useSourceControlSetup({
       unstaged: files.length - staged,
       staged,
     };
-  }, [gitFilesByPath, repoPath, scope]);
+  }, [gitFilesByPath, repoPath, sourceControlActiveRepoRoot]);
 
   const sourceControlStashCount = useStashCount({
     repoPath,
@@ -383,17 +389,22 @@ export function useSourceControlSetup({
         path: relativePath,
         repoRoot: effectiveRepoPath,
       });
+      setPrimaryPanel((state) =>
+        rememberSourceControlFocusPath(state, absolutePath)
+      );
       setSourceControlFocusTarget({ path: absolutePath, nonce: Date.now() });
 
       // AllChangesView loads content only after its target section expands.
-      // This handler deliberately remains metadata-only.
+      // Keep the click metadata-only while remembering the same path for a
+      // later hand-off to Focus mode.
     },
-    [repoPath, setGitDiffFile, setSourceControlFocusTarget]
+    [repoPath, setGitDiffFile, setPrimaryPanel, setSourceControlFocusTarget]
   );
 
   return {
     sourceControlFilterMode,
     sourceControlFilterCounts,
+    sourceControlActiveRepoRoot,
     sourceControlHeaderFilter,
     sourceControlHeaderScopePicker,
     tabSidebarExtraContext,
diff --git a/src/modules/WorkStation/Diff/SessionReplay/diffSessionReplay.useDetailContent.tsx b/src/modules/WorkStation/Diff/SessionReplay/diffSessionReplay.useDetailContent.tsx
index b26986f86..a94c5c799 100644
--- a/src/modules/WorkStation/Diff/SessionReplay/diffSessionReplay.useDetailContent.tsx
+++ b/src/modules/WorkStation/Diff/SessionReplay/diffSessionReplay.useDetailContent.tsx
@@ -16,6 +16,7 @@ import {
 } from "@src/modules/WorkStation/shared";
 import { Placeholder } from "@src/modules/shared/layouts/blocks";
 import type { SourceControlHistorySelection } from "@src/store/workstation/tabs";
+import type { DiffViewMode } from "@src/types/git/types";
 
 import type { DiffReplayTab } from "./types";
 import type { SubmissionRepoContext } from "./useSubmissionsData";
@@ -36,6 +37,7 @@ export interface UseDiffDetailContentParams {
   focusedDiffPath: string | null;
   focusedDiffNonce: number;
   collapseAllSignal: number;
+  diffViewMode: DiffViewMode;
 }
 
 export function useDiffDetailContent({
@@ -49,6 +51,7 @@ export function useDiffDetailContent({
   focusedDiffPath,
   focusedDiffNonce,
   collapseAllSignal,
+  diffViewMode,
 }: UseDiffDetailContentParams): React.ReactNode {
   const { t } = useTranslation("sessions");
   const { t: tCommon } = useTranslation("common");
@@ -122,6 +125,7 @@ export function useDiffDetailContent({
     return (
       <DiffSectionList
         sections={consolidatedSections}
+        viewMode={diffViewMode}
         loading={orgtrackFinalDiffsLoading}
         emptyTitle={t(
           "simulator.replay.diffApp.emptyForFilter",
@@ -146,6 +150,7 @@ export function useDiffDetailContent({
     focusedDiffPath,
     focusedDiffNonce,
     collapseAllSignal,
+    diffViewMode,
     t,
   ]);
 }
diff --git a/src/modules/WorkStation/Diff/SessionReplay/index.tsx b/src/modules/WorkStation/Diff/SessionReplay/index.tsx
index e30ec21e5..c46a61cd8 100644
--- a/src/modules/WorkStation/Diff/SessionReplay/index.tsx
+++ b/src/modules/WorkStation/Diff/SessionReplay/index.tsx
@@ -19,6 +19,7 @@ import React, { memo, useCallback, useEffect, useMemo, useState } from "react";
 import { useTranslation } from "react-i18next";
 
 import Button from "@src/components/Button";
+import TabPill from "@src/components/TabPill";
 import { SIMULATOR_PRIMARY_SIDEBAR } from "@src/config/simulatorPrimarySidebar";
 import { simulatorEventsAtom } from "@src/engines/SessionCore/derived/simulatorEvents";
 import type { SimulatorAppProps } from "@src/engines/Simulator/apps/core/types";
@@ -47,7 +48,9 @@ import {
   simulatorPrimarySidebarWidthAtom,
   simulatorPrimarySidebarWidthPersistAtom,
 } from "@src/store/ui/simulatorAtom";
+import { diffViewModeAtom } from "@src/store/workstation/codeEditor";
 import type { SourceControlHistorySelection } from "@src/store/workstation/tabs";
+import type { DiffViewMode } from "@src/types/git/types";
 import { confirmDestructiveAction } from "@src/util/dialogs/confirmDestructiveAction";
 
 import { isDiffScopeActive, resolveScopedSelectedPath } from "./diffScope";
@@ -82,6 +85,7 @@ const SessionReplayDiff: React.FC<SimulatorAppProps> = ({
   const [focusedDiffPath, setFocusedDiffPath] = useState<string | null>(null);
   const [focusedDiffNonce, setFocusedDiffNonce] = useState(0);
   const [collapseAllSignal, setCollapseAllSignal] = useState(0);
+  const [diffViewMode, setDiffViewMode] = useAtom(diffViewModeAtom);
   const simulatorEvents = useAtomValue(simulatorEventsAtom);
   const sessionId = useMemo(
     () =>
@@ -210,6 +214,23 @@ const SessionReplayDiff: React.FC<SimulatorAppProps> = ({
       trailing:
         activeTab === "diff" ? (
           <div className="flex items-center gap-px">
+            <TabPill
+              activeTab={diffViewMode}
+              tabs={[
+                { key: "unified", label: tCommon("workstation.unified") },
+                { key: "split", label: tCommon("workstation.split") },
+              ]}
+              onChange={(key) => setDiffViewMode(key as DiffViewMode)}
+              variant="pill"
+              color="fill"
+              fillWidth={false}
+              size="small"
+            />
+            <div
+              className="mx-1.5 h-4 w-px shrink-0 bg-border-2"
+              role="separator"
+              aria-hidden
+            />
             {canUndoAll ? (
               <Button
                 htmlType="button"
@@ -236,7 +257,15 @@ const SessionReplayDiff: React.FC<SimulatorAppProps> = ({
           </div>
         ) : undefined,
     }),
-    [activeTab, handleUndoAll, canUndoAll, handleCollapseAll, tCommon]
+    [
+      activeTab,
+      canUndoAll,
+      diffViewMode,
+      handleCollapseAll,
+      handleUndoAll,
+      setDiffViewMode,
+      tCommon,
+    ]
   );
 
   const hasSubmissions =
@@ -367,6 +396,7 @@ const SessionReplayDiff: React.FC<SimulatorAppProps> = ({
     focusedDiffPath,
     focusedDiffNonce,
     collapseAllSignal,
+    diffViewMode,
   });
 
   // A commit-detail selection (or a pending navigation request from a chat
diff --git a/src/modules/WorkStation/shared/DiffFileSection/index.tsx b/src/modules/WorkStation/shared/DiffFileSection/index.tsx
index ddcc196b5..281addf1c 100644
--- a/src/modules/WorkStation/shared/DiffFileSection/index.tsx
+++ b/src/modules/WorkStation/shared/DiffFileSection/index.tsx
@@ -26,6 +26,7 @@ import {
   useTextSelectionDropdown,
 } from "@src/scaffold/ContextMenu/exports";
 import { addToAgentAtom } from "@src/store/ui/addToAgentAtom";
+import type { DiffViewMode } from "@src/types/git/types";
 import { isBinaryByExtension } from "@src/util/file/binaryDetection";
 import {
   getPreviewType,
@@ -84,6 +85,7 @@ export interface DiffFileSectionData {
 
 export interface DiffFileSectionProps {
   file: DiffFileSectionData;
+  viewMode: DiffViewMode;
   defaultExpanded?: boolean;
   expansionSignal?: number;
   repoPath?: string;
@@ -128,6 +130,7 @@ function getFileNameAndDir(path: string): {
 
 const DiffFileSection: React.FC<DiffFileSectionProps> = ({
   file,
+  viewMode,
   defaultExpanded = true,
   expansionSignal = 0,
   repoPath,
@@ -352,7 +355,7 @@ const DiffFileSection: React.FC<DiffFileSectionProps> = ({
             oldStartLine={resolvedDiff.oldStartLine}
             newStartLine={resolvedDiff.newStartLine}
             showLineNumbers={file.showLineNumbers !== false}
-            viewMode="unified"
+            viewMode={viewMode}
             readOnly={true}
             mergeControls={false}
             collapseUnchanged={true}
diff --git a/src/modules/WorkStation/shared/DiffSectionList/index.tsx b/src/modules/WorkStation/shared/DiffSectionList/index.tsx
index 14fb69774..9dc96abaa 100644
--- a/src/modules/WorkStation/shared/DiffSectionList/index.tsx
+++ b/src/modules/WorkStation/shared/DiffSectionList/index.tsx
@@ -2,6 +2,7 @@ import React, { memo, useCallback, useEffect, useMemo, useRef } from "react";
 import { Virtuoso, type VirtuosoHandle } from "react-virtuoso";
 
 import { Placeholder } from "@src/modules/shared/layouts/blocks";
+import type { DiffViewMode } from "@src/types/git/types";
 
 import DiffFileSection from "../DiffFileSection";
 import type { DiffFileSectionData } from "../DiffFileSection";
@@ -14,6 +15,7 @@ export interface DiffSectionListItem<TFile extends DiffFileSectionData> {
 
 export interface DiffSectionListProps<TFile extends DiffFileSectionData> {
   sections: Array<DiffSectionListItem<TFile>>;
+  viewMode: DiffViewMode;
   loading?: boolean;
   emptyTitle: string;
   emptySubtitle?: string;
@@ -53,6 +55,7 @@ const DIFF_LIST_COMPONENTS = { Footer: DiffListFooter };
 
 function DiffSectionListInner<TFile extends DiffFileSectionData>({
   sections,
+  viewMode,
   loading = false,
   emptyTitle,
   emptySubtitle,
@@ -197,6 +200,7 @@ function DiffSectionListInner<TFile extends DiffFileSectionData>({
             return (
               <DiffFileSection
                 file={section.file}
+                viewMode={viewMode}
                 defaultExpanded={
                   expandedOverride ??
                   getDefaultDiffSectionExpanded({
diff --git a/src/modules/shared/components/FileHeader/index.tsx b/src/modules/shared/components/FileHeader/index.tsx
index 94ac5c871..2d92ad497 100644
--- a/src/modules/shared/components/FileHeader/index.tsx
+++ b/src/modules/shared/components/FileHeader/index.tsx
@@ -28,6 +28,7 @@ import { HEADER_ICON_SIZE } from "@src/config/workstation/tokens";
 import { useRefreshSpin } from "@src/hooks/ui";
 import { type WorkstationTabHeaderHost } from "@src/hooks/workStation";
 import { PANEL_HEADER_TOKENS } from "@src/modules/shared/layouts/blocks/PanelHeader";
+import type { DiffViewMode } from "@src/types/git/types";
 import { copyText } from "@src/util/data/clipboard";
 
 import BreadcrumbFileHeader from "./BreadcrumbFileHeader";
@@ -36,7 +37,7 @@ import { FileHeaderShell } from "./FileHeaderShell";
 
 const RELOAD_MENU_COOLDOWN_MS = 1200;
 
-export type DiffViewMode = "unified" | "split";
+export type { DiffViewMode } from "@src/types/git/types";
 
 export interface ToggleOption {
   value: string;
diff --git a/src/store/workstation/codeEditor/diffViewModeAtom.test.ts b/src/store/workstation/codeEditor/diffViewModeAtom.test.ts
new file mode 100644
index 000000000..16dd6cb92
--- /dev/null
+++ b/src/store/workstation/codeEditor/diffViewModeAtom.test.ts
@@ -0,0 +1,42 @@
+import { createStore } from "jotai";
+import { beforeEach, describe, expect, it } from "vitest";
+
+import {
+  DEFAULT_DIFF_VIEW_MODE,
+  DIFF_VIEW_MODE_STORAGE_KEY,
+  diffViewModeAtom,
+  normalizeDiffViewMode,
+} from "./diffViewModeAtom";
+
+beforeEach(() => {
+  localStorage.removeItem(DIFF_VIEW_MODE_STORAGE_KEY);
+});
+
+describe("normalizeDiffViewMode", () => {
+  it("preserves supported persisted values", () => {
+    expect(normalizeDiffViewMode("unified")).toBe("unified");
+    expect(normalizeDiffViewMode("split")).toBe("split");
+  });
+
+  it("falls back safely when persisted data is stale or malformed", () => {
+    expect(normalizeDiffViewMode("side-by-side")).toBe(DEFAULT_DIFF_VIEW_MODE);
+    expect(normalizeDiffViewMode(null)).toBe(DEFAULT_DIFF_VIEW_MODE);
+  });
+
+  it("persists the latest user choice for a fresh store after reload", () => {
+    const writerStore = createStore();
+    const unsubscribeWriter = writerStore.sub(diffViewModeAtom, () => {});
+
+    writerStore.set(diffViewModeAtom, "split");
+
+    expect(localStorage.getItem(DIFF_VIEW_MODE_STORAGE_KEY)).toBe('"split"');
+    unsubscribeWriter();
+
+    const readerStore = createStore();
+    const unsubscribeReader = readerStore.sub(diffViewModeAtom, () => {});
+
+    expect(readerStore.get(diffViewModeAtom)).toBe("split");
+
+    unsubscribeReader();
+  });
+});
diff --git a/src/store/workstation/codeEditor/diffViewModeAtom.ts b/src/store/workstation/codeEditor/diffViewModeAtom.ts
new file mode 100644
index 000000000..f6c91c919
--- /dev/null
+++ b/src/store/workstation/codeEditor/diffViewModeAtom.ts
@@ -0,0 +1,28 @@
+import { atom } from "jotai";
+import { atomWithStorage } from "jotai/utils";
+
+import type { DiffViewMode } from "@src/types/git/types";
+
+export const DIFF_VIEW_MODE_STORAGE_KEY = "orgii:gitDiffViewMode";
+export const DEFAULT_DIFF_VIEW_MODE: DiffViewMode = "unified";
+
+export function normalizeDiffViewMode(value: unknown): DiffViewMode {
+  return value === "split" ? "split" : DEFAULT_DIFF_VIEW_MODE;
+}
+
+const persistedDiffViewModeAtom = atomWithStorage<unknown>(
+  DIFF_VIEW_MODE_STORAGE_KEY,
+  DEFAULT_DIFF_VIEW_MODE
+);
+
+/**
+ * Authoritative diff presentation preference shared by working-tree, commit,
+ * pull-request, aggregate, and replay diff surfaces.
+ */
+export const diffViewModeAtom = atom(
+  (get) => normalizeDiffViewMode(get(persistedDiffViewModeAtom)),
+  (_get, set, mode: DiffViewMode) => {
+    set(persistedDiffViewModeAtom, mode);
+  }
+);
+diffViewModeAtom.debugLabel = "codeEditor/diffViewMode";
diff --git a/src/store/workstation/codeEditor/index.ts b/src/store/workstation/codeEditor/index.ts
index 029899e6f..74cb4f1ec 100644
--- a/src/store/workstation/codeEditor/index.ts
+++ b/src/store/workstation/codeEditor/index.ts
@@ -29,6 +29,9 @@ export * from "./workspacePortsAtom";
 // Git diff review bar (change list position)
 export * from "./gitReviewNavigationAtom";
 
+// Shared unified/split presentation preference for git diff surfaces
+export * from "./diffViewModeAtom";
+
 // Source Control focus target (sidebar click → scroll/expand in All Changes view)
 export * from "./sourceControlFocusTargetAtom";
 
diff --git a/src/types/git/types.ts b/src/types/git/types.ts
index a033b2512..3520ae04b 100644
--- a/src/types/git/types.ts
+++ b/src/types/git/types.ts
@@ -11,6 +11,9 @@
  */
 import type { GitFileStatus } from "@src/config/gitStatus";
 
+/** Shared presentation mode for Git review diff surfaces. */
+export type DiffViewMode = "unified" | "split";
+
 // Re-export GitFileStatus for convenience
 export type { GitFileStatus } from "@src/config/gitStatus";
 

From 2216f06ee3699797ef6edf7ba1ae3ee3cdd0ac12 Mon Sep 17 00:00:00 2001
From: Harry19081 <20519290+Harry19081@users.noreply.github.com>
Date: Thu, 6 Aug 2026 23:12:33 +0800
Subject: [PATCH 2/2] fix(ui): tolerate missing ResizeObserver

Pre-commit hook ran. Total eslint: 0, total circular: 0
---
 .../ui/layout/useElementDimensions.test.ts    | 103 ++++++++++++++++++
 src/hooks/ui/layout/useElementDimensions.ts   |   2 +-
 2 files changed, 104 insertions(+), 1 deletion(-)
 create mode 100644 src/hooks/ui/layout/useElementDimensions.test.ts

diff --git a/src/hooks/ui/layout/useElementDimensions.test.ts b/src/hooks/ui/layout/useElementDimensions.test.ts
new file mode 100644
index 000000000..8a4b0f999
--- /dev/null
+++ b/src/hooks/ui/layout/useElementDimensions.test.ts
@@ -0,0 +1,103 @@
+// @vitest-environment jsdom
+import React, { act, createElement, useRef } from "react";
+import { type Root, createRoot } from "react-dom/client";
+import {
+  afterAll,
+  afterEach,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+} from "vitest";
+
+import { useElementDimensions } from "./useElementDimensions";
+
+function DimensionProbe(): React.ReactNode {
+  const elementRef = useRef<HTMLDivElement>(null);
+  const dimensions = useElementDimensions(elementRef);
+
+  // eslint-disable-next-line react-hooks/refs -- createElement is required because Vitest only includes `.test.ts`; this is a normal React ref prop.
+  return createElement("div", {
+    ref: elementRef,
+    "data-testid": "dimension-probe",
+    "data-dimensions": `${dimensions.width}x${dimensions.height}`,
+  });
+}
+
+describe("useElementDimensions", () => {
+  let container: HTMLDivElement;
+  let root: Root;
+  const actEnvironment = globalThis as typeof globalThis & {
+    IS_REACT_ACT_ENVIRONMENT?: boolean;
+  };
+
+  beforeAll(() => {
+    actEnvironment.IS_REACT_ACT_ENVIRONMENT = true;
+  });
+
+  beforeEach(() => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    root = createRoot(container);
+  });
+
+  afterEach(() => {
+    act(() => root.unmount());
+    container.remove();
+    vi.unstubAllGlobals();
+    vi.restoreAllMocks();
+  });
+
+  afterAll(() => {
+    Reflect.deleteProperty(actEnvironment, "IS_REACT_ACT_ENVIRONMENT");
+  });
+
+  it("keeps the window resize fallback when ResizeObserver is unavailable", () => {
+    vi.stubGlobal("ResizeObserver", undefined);
+    const addWindowListener = vi.spyOn(window, "addEventListener");
+    const removeWindowListener = vi.spyOn(window, "removeEventListener");
+
+    expect(() => {
+      act(() => root.render(createElement(DimensionProbe)));
+    }).not.toThrow();
+
+    expect(addWindowListener).toHaveBeenCalledWith(
+      "resize",
+      expect.any(Function)
+    );
+
+    act(() => root.unmount());
+    root = createRoot(container);
+
+    expect(removeWindowListener).toHaveBeenCalledWith(
+      "resize",
+      expect.any(Function)
+    );
+  });
+
+  it("disconnects the observer when the measured element unmounts", () => {
+    const observe = vi.fn();
+    const disconnect = vi.fn();
+    vi.stubGlobal(
+      "ResizeObserver",
+      class ResizeObserverMock {
+        observe = observe;
+        unobserve = vi.fn();
+        disconnect = disconnect;
+      }
+    );
+
+    act(() => root.render(createElement(DimensionProbe)));
+
+    expect(observe).toHaveBeenCalledWith(
+      container.querySelector('[data-testid="dimension-probe"]')
+    );
+
+    act(() => root.unmount());
+    root = createRoot(container);
+
+    expect(disconnect).toHaveBeenCalledOnce();
+  });
+});
diff --git a/src/hooks/ui/layout/useElementDimensions.ts b/src/hooks/ui/layout/useElementDimensions.ts
index f65ba34a1..36d2001ce 100644
--- a/src/hooks/ui/layout/useElementDimensions.ts
+++ b/src/hooks/ui/layout/useElementDimensions.ts
@@ -122,7 +122,7 @@ export function useElementDimensions(
 
     // Set up ResizeObserver for accurate tracking
     let resizeObserver: ResizeObserver | null = null;
-    if (element) {
+    if (element && typeof ResizeObserver !== "undefined") {
       resizeObserver = new ResizeObserver(measureDimensions);
       resizeObserver.observe(element);
     }