diff --git a/apps/array/src/main/preload.ts b/apps/array/src/main/preload.ts
index 7e9ca34f..a766ca78 100644
--- a/apps/array/src/main/preload.ts
+++ b/apps/array/src/main/preload.ts
@@ -257,6 +257,12 @@ contextBridge.exposeInMainWorld("electronAPI", {
     ipcRenderer.invoke("save-question-answers", repoPath, taskId, answers),
   readRepoFile: (repoPath: string, filePath: string): Promise<string | null> =>
     ipcRenderer.invoke("read-repo-file", repoPath, filePath),
+  writeRepoFile: (
+    repoPath: string,
+    filePath: string,
+    content: string,
+  ): Promise<void> =>
+    ipcRenderer.invoke("write-repo-file", repoPath, filePath, content),
   getChangedFilesHead: (
     repoPath: string,
   ): Promise<Array<{ path: string; status: string; originalPath?: string }>> =>
diff --git a/apps/array/src/main/services/fs.ts b/apps/array/src/main/services/fs.ts
index f9611152..48b416c2 100644
--- a/apps/array/src/main/services/fs.ts
+++ b/apps/array/src/main/services/fs.ts
@@ -434,4 +434,31 @@ export function registerFsIpc(): void {
       }
     },
   );
+
+  ipcMain.handle(
+    "write-repo-file",
+    async (
+      _event: IpcMainInvokeEvent,
+      repoPath: string,
+      filePath: string,
+      content: string,
+    ): Promise<void> => {
+      try {
+        const fullPath = path.join(repoPath, filePath);
+        const resolvedPath = path.resolve(fullPath);
+        const resolvedRepo = path.resolve(repoPath);
+        if (!resolvedPath.startsWith(resolvedRepo)) {
+          throw new Error("Access denied: path outside repository");
+        }
+
+        await fsPromises.writeFile(fullPath, content, "utf-8");
+        log.debug(`Wrote file ${filePath} to ${repoPath}`);
+
+        repoFileCache.delete(repoPath);
+      } catch (error) {
+        log.error(`Failed to write file ${filePath} to ${repoPath}:`, error);
+        throw error;
+      }
+    },
+  );
 }
diff --git a/apps/array/src/renderer/features/code-editor/components/CodeMirrorDiffEditor.tsx b/apps/array/src/renderer/features/code-editor/components/CodeMirrorDiffEditor.tsx
index 858918d3..c0e8cce7 100644
--- a/apps/array/src/renderer/features/code-editor/components/CodeMirrorDiffEditor.tsx
+++ b/apps/array/src/renderer/features/code-editor/components/CodeMirrorDiffEditor.tsx
@@ -9,12 +9,14 @@ interface CodeMirrorDiffEditorProps {
   originalContent: string;
   modifiedContent: string;
   filePath?: string;
+  onContentChange?: (content: string) => void;
 }
 
 export function CodeMirrorDiffEditor({
   originalContent,
   modifiedContent,
   filePath,
+  onContentChange,
 }: CodeMirrorDiffEditorProps) {
   const [viewMode, setViewMode] = useState<ViewMode>("split");
   const extensions = useEditorExtensions(filePath, true);
@@ -25,8 +27,16 @@ export function CodeMirrorDiffEditor({
       extensions,
       mode: viewMode,
       filePath,
+      onContentChange,
     }),
-    [originalContent, modifiedContent, extensions, viewMode, filePath],
+    [
+      originalContent,
+      modifiedContent,
+      extensions,
+      viewMode,
+      filePath,
+      onContentChange,
+    ],
   );
   const containerRef = useCodeMirror(options);
 
diff --git a/apps/array/src/renderer/features/code-editor/components/DiffEditorPanel.tsx b/apps/array/src/renderer/features/code-editor/components/DiffEditorPanel.tsx
index 8cbce24a..41398d03 100644
--- a/apps/array/src/renderer/features/code-editor/components/DiffEditorPanel.tsx
+++ b/apps/array/src/renderer/features/code-editor/components/DiffEditorPanel.tsx
@@ -5,7 +5,8 @@ import { getRelativePath } from "@features/code-editor/utils/pathUtils";
 import { useTaskData } from "@features/task-detail/hooks/useTaskData";
 import { Box } from "@radix-ui/themes";
 import type { Task } from "@shared/types";
-import { useQuery } from "@tanstack/react-query";
+import { useQuery, useQueryClient } from "@tanstack/react-query";
+import { useCallback } from "react";
 import {
   selectWorktreePath,
   useWorkspaceStore,
@@ -26,6 +27,7 @@ export function DiffEditorPanel({
   const worktreePath = useWorkspaceStore(selectWorktreePath(taskId));
   const repoPath = worktreePath ?? taskData.repoPath;
   const filePath = getRelativePath(absolutePath, repoPath);
+  const queryClient = useQueryClient();
 
   const { data: changedFiles = [] } = useQuery({
     queryKey: ["changed-files-head", repoPath],
@@ -56,6 +58,24 @@ export function DiffEditorPanel({
     staleTime: Infinity,
   });
 
+  const handleContentChange = useCallback(
+    async (newContent: string) => {
+      if (!repoPath) return;
+
+      try {
+        await window.electronAPI.writeRepoFile(repoPath, filePath, newContent);
+
+        queryClient.invalidateQueries({
+          queryKey: ["repo-file", repoPath, filePath],
+        });
+        queryClient.invalidateQueries({
+          queryKey: ["changed-files-head", repoPath],
+        });
+      } catch (_error) {}
+    },
+    [repoPath, filePath, queryClient],
+  );
+
   if (!repoPath) {
     return <PanelMessage>No repository path available</PanelMessage>;
   }
@@ -76,6 +96,7 @@ export function DiffEditorPanel({
           originalContent={originalContent ?? ""}
           modifiedContent={modifiedContent ?? ""}
           filePath={absolutePath}
+          onContentChange={handleContentChange}
         />
       ) : (
         <CodeMirrorEditor
diff --git a/apps/array/src/renderer/features/code-editor/hooks/useCodeMirror.ts b/apps/array/src/renderer/features/code-editor/hooks/useCodeMirror.ts
index 897bff97..241e6a2e 100644
--- a/apps/array/src/renderer/features/code-editor/hooks/useCodeMirror.ts
+++ b/apps/array/src/renderer/features/code-editor/hooks/useCodeMirror.ts
@@ -1,4 +1,9 @@
-import { MergeView, unifiedMergeView } from "@codemirror/merge";
+import {
+  acceptChunk,
+  MergeView,
+  rejectChunk,
+  unifiedMergeView,
+} from "@codemirror/merge";
 import { EditorState, type Extension } from "@codemirror/state";
 import { EditorView } from "@codemirror/view";
 import { handleExternalAppAction } from "@utils/handleExternalAppAction";
@@ -19,8 +24,44 @@ interface DiffOptions extends UseCodeMirrorOptions {
   original: string;
   modified: string;
   mode: "split" | "unified";
+  onContentChange?: (content: string) => void;
 }
 
+const createMergeControls = (onReject?: () => void) => {
+  return (type: "accept" | "reject", action: (e: MouseEvent) => void) => {
+    if (type === "accept") {
+      return document.createElement("span");
+    }
+
+    const button = document.createElement("button");
+    button.textContent = "Reject";
+    button.name = "reject";
+    button.style.background = "var(--red-9)";
+    button.style.color = "white";
+    button.style.border = "none";
+    button.style.padding = "2px 6px";
+    button.style.borderRadius = "3px";
+    button.style.cursor = "pointer";
+    button.style.fontSize = "11px";
+
+    button.onmousedown = (e) => {
+      action(e);
+      onReject?.();
+    };
+
+    return button;
+  };
+};
+
+const getBaseDiffConfig = (
+  onReject?: () => void,
+): Partial<Parameters<typeof unifiedMergeView>[0]> => ({
+  collapseUnchanged: { margin: 3, minSize: 4 },
+  highlightChanges: false,
+  gutter: true,
+  mergeControls: createMergeControls(onReject),
+});
+
 export function useCodeMirror(options: SingleDocOptions | DiffOptions) {
   const containerRef = useRef<HTMLDivElement>(null);
   const instanceRef = useRef<EditorInstance | null>(null);
@@ -40,21 +81,63 @@ export function useCodeMirror(options: SingleDocOptions | DiffOptions) {
         parent: containerRef.current,
       });
     } else if (options.mode === "split") {
+      const diffConfig = getBaseDiffConfig(
+        options.onContentChange
+          ? () => {
+              if (instanceRef.current instanceof MergeView) {
+                const content = instanceRef.current.b.state.doc.toString();
+                options.onContentChange?.(content);
+              }
+            }
+          : undefined,
+      );
+
+      const updateListener = options.onContentChange
+        ? EditorView.updateListener.of((update) => {
+            if (
+              update.docChanged &&
+              update.transactions.some((tr) => tr.isUserEvent("revert"))
+            ) {
+              const content = update.state.doc.toString();
+              options.onContentChange?.(content);
+            }
+          })
+        : [];
+
       instanceRef.current = new MergeView({
         a: { doc: options.original, extensions: options.extensions },
-        b: { doc: options.modified, extensions: options.extensions },
+        b: {
+          doc: options.modified,
+          extensions: [
+            ...options.extensions,
+            ...(Array.isArray(updateListener)
+              ? updateListener
+              : [updateListener]),
+          ],
+        },
+        ...diffConfig,
         parent: containerRef.current,
+        revertControls: "a-to-b",
       });
     } else {
+      const diffConfig = getBaseDiffConfig(
+        options.onContentChange
+          ? () => {
+              if (instanceRef.current instanceof EditorView) {
+                const content = instanceRef.current.state.doc.toString();
+                options.onContentChange?.(content);
+              }
+            }
+          : undefined,
+      );
+
       instanceRef.current = new EditorView({
         doc: options.modified,
         extensions: [
           ...options.extensions,
           unifiedMergeView({
             original: options.original,
-            highlightChanges: true,
-            gutter: true,
-            mergeControls: false,
+            ...diffConfig,
           }),
         ],
         parent: containerRef.current,
@@ -95,3 +178,5 @@ export function useCodeMirror(options: SingleDocOptions | DiffOptions) {
 
   return containerRef;
 }
+
+export { acceptChunk, rejectChunk };
diff --git a/apps/array/src/renderer/features/code-editor/hooks/useEditorExtensions.ts b/apps/array/src/renderer/features/code-editor/hooks/useEditorExtensions.ts
index 14f227d6..877bdd60 100644
--- a/apps/array/src/renderer/features/code-editor/hooks/useEditorExtensions.ts
+++ b/apps/array/src/renderer/features/code-editor/hooks/useEditorExtensions.ts
@@ -6,7 +6,7 @@ import {
 } from "@codemirror/view";
 import { useThemeStore } from "@stores/themeStore";
 import { useMemo } from "react";
-import { oneDark, oneLight } from "../theme/editorTheme";
+import { mergeViewTheme, oneDark, oneLight } from "../theme/editorTheme";
 import { getLanguageExtension } from "../utils/languages";
 
 export function useEditorExtensions(filePath?: string, readOnly = false) {
@@ -20,6 +20,7 @@ export function useEditorExtensions(filePath?: string, readOnly = false) {
       lineNumbers(),
       highlightActiveLineGutter(),
       theme,
+      mergeViewTheme,
       EditorView.editable.of(!readOnly),
       ...(readOnly ? [EditorState.readOnly.of(true)] : []),
       ...(languageExtension ? [languageExtension] : []),
diff --git a/apps/array/src/renderer/features/code-editor/theme/editorTheme.ts b/apps/array/src/renderer/features/code-editor/theme/editorTheme.ts
index c34dc7ad..b16d5a92 100644
--- a/apps/array/src/renderer/features/code-editor/theme/editorTheme.ts
+++ b/apps/array/src/renderer/features/code-editor/theme/editorTheme.ts
@@ -197,3 +197,116 @@ export const oneLight: Extension = [
   createEditorTheme(light, false),
   syntaxHighlighting(createHighlightStyle(light)),
 ];
+
+export const mergeViewTheme = EditorView.baseTheme({
+  ".cm-mergeView": {
+    overflowY: "auto",
+  },
+  ".cm-mergeViewEditors": {
+    display: "flex",
+    alignItems: "stretch",
+  },
+  ".cm-mergeViewEditor": {
+    flexGrow: "1",
+    flexBasis: "0",
+    overflow: "hidden",
+  },
+  ".cm-merge-revert": {
+    width: "1.6em",
+    flexGrow: "0",
+    flexShrink: "0",
+    position: "relative",
+  },
+  ".cm-merge-revert button": {
+    position: "absolute",
+    display: "block",
+    width: "100%",
+    boxSizing: "border-box",
+    textAlign: "center",
+    background: "none",
+    border: "none",
+    font: "inherit",
+    cursor: "pointer",
+  },
+  ".cm-mergeView & .cm-scroller, .cm-mergeView &": {
+    height: "auto !important",
+    overflowY: "visible !important",
+  },
+  "&.cm-merge-a .cm-changedLine, .cm-deletedChunk": {
+    backgroundColor: "rgba(160, 128, 100, .08)",
+  },
+  "&.cm-merge-b .cm-changedLine, .cm-inlineChangedLine": {
+    backgroundColor: "rgba(100, 160, 128, .08)",
+  },
+  "&light.cm-merge-a .cm-changedText, &light .cm-deletedChunk .cm-deletedText":
+    {
+      background:
+        "linear-gradient(#ee443366, #ee443366) bottom/100% 2px no-repeat",
+    },
+  "&dark.cm-merge-a .cm-changedText, &dark .cm-deletedChunk .cm-deletedText": {
+    background:
+      "linear-gradient(#ffaa9966, #ffaa9966) bottom/100% 2px no-repeat",
+  },
+  "&light.cm-merge-b .cm-changedText": {
+    background:
+      "linear-gradient(#22bb22aa, #22bb22aa) bottom/100% 2px no-repeat",
+  },
+  "&dark.cm-merge-b .cm-changedText": {
+    background:
+      "linear-gradient(#88ff88aa, #88ff88aa) bottom/100% 2px no-repeat",
+  },
+  "&.cm-merge-b .cm-deletedText": {
+    background: "#ff000033",
+  },
+  ".cm-insertedLine, .cm-deletedLine, .cm-deletedLine del": {
+    textDecoration: "none",
+  },
+  ".cm-deletedChunk": {
+    paddingLeft: "6px",
+    "& .cm-chunkButtons": {
+      position: "absolute",
+      insetInlineEnd: "5px",
+    },
+    "& button": {
+      border: "none",
+      cursor: "pointer",
+      color: "white",
+      margin: "0 2px",
+      borderRadius: "3px",
+      "&[name=accept]": { background: "#2a2" },
+      "&[name=reject]": { background: "#d43" },
+    },
+  },
+  ".cm-collapsedLines": {
+    padding: "5px 5px 5px 10px",
+    cursor: "pointer",
+    "&:before": {
+      content: '"⦚"',
+      marginInlineEnd: "7px",
+    },
+    "&:after": {
+      content: '"⦚"',
+      marginInlineStart: "7px",
+    },
+  },
+  "&light .cm-collapsedLines": {
+    color: "#444",
+    background:
+      "linear-gradient(to bottom, transparent 0, #f3f3f3 30%, #f3f3f3 70%, transparent 100%)",
+  },
+  "&dark .cm-collapsedLines": {
+    color: "#ddd",
+    background:
+      "linear-gradient(to bottom, transparent 0, #222 30%, #222 70%, transparent 100%)",
+  },
+  ".cm-changeGutter": { width: "3px", paddingLeft: "1px" },
+  "&light.cm-merge-a .cm-changedLineGutter, &light .cm-deletedLineGutter": {
+    background: "#e43",
+  },
+  "&dark.cm-merge-a .cm-changedLineGutter, &dark .cm-deletedLineGutter": {
+    background: "#fa9",
+  },
+  "&light.cm-merge-b .cm-changedLineGutter": { background: "#2b2" },
+  "&dark.cm-merge-b .cm-changedLineGutter": { background: "#8f8" },
+  ".cm-inlineChangedLineGutter": { background: "#75d" },
+});
diff --git a/apps/array/src/renderer/features/editor/components/MarkdownRenderer.tsx b/apps/array/src/renderer/features/editor/components/MarkdownRenderer.tsx
index 525d4c0f..7d1d9272 100644
--- a/apps/array/src/renderer/features/editor/components/MarkdownRenderer.tsx
+++ b/apps/array/src/renderer/features/editor/components/MarkdownRenderer.tsx
@@ -34,22 +34,22 @@ const fontStyle = {
 
 const components: Components = {
   h1: ({ children }) => (
-    <Heading as="h1" size="5" mb="3" color="gray" highContrast>
+    <Heading as="h1" size="4" mb="3" color="gray" highContrast>
       {children}
     </Heading>
   ),
   h2: ({ children }) => (
-    <Heading as="h2" size="4" mb="3" color="gray" highContrast>
+    <Heading as="h2" size="3" mb="3" color="gray" highContrast>
       {children}
     </Heading>
   ),
   h3: ({ children }) => (
-    <Heading as="h3" size="3" mb="2" color="gray" highContrast>
+    <Heading as="h3" size="2" mb="2" color="gray" highContrast>
       {children}
     </Heading>
   ),
   h4: ({ children }) => (
-    <Heading as="h4" size="3" mb="2" color="gray" highContrast>
+    <Heading as="h4" size="2" mb="2" color="gray" highContrast>
       {children}
     </Heading>
   ),
diff --git a/apps/array/src/renderer/features/sessions/components/VirtualizedList.tsx b/apps/array/src/renderer/features/sessions/components/VirtualizedList.tsx
index 30ca7ac8..7bccd9e8 100644
--- a/apps/array/src/renderer/features/sessions/components/VirtualizedList.tsx
+++ b/apps/array/src/renderer/features/sessions/components/VirtualizedList.tsx
@@ -1,5 +1,11 @@
 import { useVirtualizer } from "@tanstack/react-virtual";
-import { type ReactNode, useCallback, useEffect, useRef } from "react";
+import {
+  type ReactNode,
+  useCallback,
+  useEffect,
+  useLayoutEffect,
+  useRef,
+} from "react";
 
 interface VirtualizedListProps<T> {
   items: T[];
@@ -26,6 +32,7 @@ export function VirtualizedList<T>({
 }: VirtualizedListProps<T>) {
   const scrollRef = useRef<HTMLDivElement>(null);
   const isAtBottomRef = useRef(true);
+  const isInitialMountRef = useRef(true);
 
   const virtualizer = useVirtualizer({
     count: items.length,
@@ -53,11 +60,44 @@ export function VirtualizedList<T>({
     return () => el.removeEventListener("scroll", handleScroll);
   }, [handleScroll]);
 
+  useLayoutEffect(() => {
+    const el = scrollRef.current;
+    if (!el || !autoScrollToBottom || items.length === 0) {
+      return;
+    }
+
+    if (isInitialMountRef.current) {
+      isInitialMountRef.current = false;
+      el.scrollTop = el.scrollHeight;
+      return;
+    }
+  }, [autoScrollToBottom, items.length]);
+
   useEffect(() => {
-    if (autoScrollToBottom && isAtBottomRef.current && items.length > 0) {
-      virtualizer.scrollToIndex(items.length - 1, { align: "end" });
+    const el = scrollRef.current;
+    if (
+      !el ||
+      !autoScrollToBottom ||
+      items.length === 0 ||
+      isInitialMountRef.current
+    ) {
+      return;
+    }
+
+    if (!isAtBottomRef.current) {
+      return;
     }
-  }, [autoScrollToBottom, items.length, virtualizer]);
+
+    const scrollToBottom = () => {
+      const el = scrollRef.current;
+      if (el) {
+        el.scrollTop = el.scrollHeight;
+      }
+    };
+    requestAnimationFrame(() => {
+      requestAnimationFrame(scrollToBottom);
+    });
+  }, [autoScrollToBottom, items]);
 
   if (items.length === 0) {
     return null;
diff --git a/apps/array/src/renderer/types/electron.d.ts b/apps/array/src/renderer/types/electron.d.ts
index f7aa9a65..cab9ff03 100644
--- a/apps/array/src/renderer/types/electron.d.ts
+++ b/apps/array/src/renderer/types/electron.d.ts
@@ -179,6 +179,11 @@ declare global {
       repoPath: string,
       filePath: string,
     ) => Promise<string | null>;
+    writeRepoFile: (
+      repoPath: string,
+      filePath: string,
+      content: string,
+    ) => Promise<void>;
     getChangedFilesHead: (repoPath: string) => Promise<ChangedFile[]>;
     getFileAtHead: (
       repoPath: string,