diff --git a/apps/web/src/components/files/FilePreviewPanel.browser.test.tsx b/apps/web/src/components/files/FilePreviewPanel.browser.test.tsx
index 49857b5db36a4..16a7b74c4ac71 100644
--- a/apps/web/src/components/files/FilePreviewPanel.browser.test.tsx
+++ b/apps/web/src/components/files/FilePreviewPanel.browser.test.tsx
@@ -1,7 +1,16 @@
+import { DEFAULT_THEMES, preloadHighlighter } from "@pierre/diffs";
 import { EnvironmentId, ThreadId, type ProjectReadFileResult } from "@t3tools/contracts";
 import { AsyncResult } from "effect/reactivity";
+import type { ReactNode } from "react";
 import { describe, expect, it, vi } from "vite-plus/test";
+import { userEvent } from "vite-plus/test/browser";
 import { act, fakeTimers, render } from "../../../test/render";
+import appCss from "~/index.css?inline";
+import {
+  createWorkspaceFocusController,
+  startWorkspaceFocus,
+  workspaceAreaProps,
+} from "~/lib/workspaceFocus";
 
 const state = vi.hoisted(() => ({
   file: null as ProjectReadFileResult | null,
@@ -49,6 +58,21 @@ vi.mock(import("~/hooks/useWorkspaceMutationRefresh"), () => ({
   useWorkspaceMutationRefresh: vi.fn(),
 }));
 vi.mock(import("./FileBreadcrumbs"), () => ({ FileBreadcrumbs: () => <></> }));
+vi.mock(import("./FileBrowserPanel"), () => ({
+  default: () => (
+    <div role="tree">
+      <button type="button" role="treeitem" data-item-path="src/">
+        src
+      </button>
+      <button type="button" role="treeitem" data-item-path="server.ts">
+        server.ts
+      </button>
+    </div>
+  ),
+}));
+vi.mock(import("../DiffWorkerPoolProvider"), () => ({
+  DiffWorkerPoolProvider: ({ children }: { children?: ReactNode }) => <>{children}</>,
+}));
 vi.mock(import("./projectFilesQueryState"), async (original) => ({
   ...(await original()),
   useProjectFileQuery: () => ({
@@ -82,6 +106,7 @@ function setup() {
   const previous = keys.map((key) => localStorage.getItem(key));
   localStorage.setItem(keys[0]!, "false");
   localStorage.setItem(keys[1]!, "true");
+  state.file = null;
   state.optimistic = null;
   state.writeFile.mockReset().mockResolvedValue(AsyncResult.success(undefined));
   return {
@@ -102,12 +127,16 @@ function markdownPreview(truncated: boolean) {
     byteLength: truncated ? 1_200_000 : 32,
     truncated,
   };
+  return filePreview("tasks.md");
+}
+
+function filePreview(relativePath: string) {
   return (
     <FilePreviewPanel
       environmentId={environmentId}
       cwd="/workspace"
       projectName="Project"
-      relativePath="tasks.md"
+      relativePath={relativePath}
       threadRef={threadRef}
       composerDraftTarget={threadRef}
       keybindings={[]}
@@ -125,6 +154,80 @@ function markdownPreview(truncated: boolean) {
   );
 }
 
+function deepActiveElement() {
+  let active = document.activeElement;
+  while (active?.shadowRoot?.activeElement) active = active.shadowRoot.activeElement;
+  return active;
+}
+
+describe("source file focus", () => {
+  it("moves panel focus into the source editor once the file loads", async () => {
+    using _settings = setup();
+    const style = document.createElement("style");
+    style.textContent = appCss;
+    document.head.append(style);
+    using _style = { [Symbol.dispose]: () => style.remove() };
+    await preloadHighlighter({ themes: Object.values(DEFAULT_THEMES), langs: ["typescript"] });
+    const panel = () => (
+      <div {...workspaceAreaProps("panel", 1, "Workspace panel")}>
+        <div data-right-panel-surface-content>{filePreview("server.ts")}</div>
+      </div>
+    );
+    const editorHasFocus = () => expect(deepActiveElement()?.matches("[data-content]")).toBe(true);
+
+    await using screen = await render(panel());
+    const focus = createWorkspaceFocusController(document);
+    using _focus = { [Symbol.dispose]: focus.dispose };
+    expect(focus.focus("panel")).toBe(true);
+    state.file = {
+      relativePath: "server.ts",
+      contents: "const server = 1;\n",
+      byteLength: 18,
+      truncated: false,
+    };
+    await screen.rerender(panel());
+    await vi.waitFor(editorHasFocus);
+  });
+
+  it("focuses the editor when a file row is clicked or activated with Enter", async () => {
+    using _settings = setup();
+    localStorage.setItem("t3code.fileExplorerOpen", "true");
+    const style = document.createElement("style");
+    style.textContent = appCss;
+    document.head.append(style);
+    using _style = { [Symbol.dispose]: () => style.remove() };
+    await preloadHighlighter({ themes: Object.values(DEFAULT_THEMES), langs: ["typescript"] });
+    state.file = {
+      relativePath: "server.ts",
+      contents: "const server = 1;\n",
+      byteLength: 18,
+      truncated: false,
+    };
+    await using screen = await render(
+      <div {...workspaceAreaProps("panel", 1, "Workspace panel")}>
+        <div data-right-panel-surface-content>{filePreview("server.ts")}</div>
+      </div>,
+    );
+    using _focus = {
+      [Symbol.dispose]: startWorkspaceFocus({ subscribe: () => () => {} } as never),
+    };
+    const editorHasFocus = () => expect(deepActiveElement()?.matches("[data-content]")).toBe(true);
+    const folderRow = screen.getByRole("treeitem", { name: "src" });
+    const fileRow = screen.getByRole("treeitem", { name: "server.ts" });
+
+    (folderRow.element() as HTMLElement).focus();
+    await userEvent.keyboard("{Enter}");
+    expect(document.activeElement).toBe(folderRow.element());
+
+    await userEvent.click(fileRow);
+    await vi.waitFor(editorHasFocus);
+
+    (fileRow.element() as HTMLElement).focus();
+    await userEvent.keyboard("{Enter}");
+    await vi.waitFor(editorHasFocus);
+  });
+});
+
 describe("rendered Markdown task saves", () => {
   it("keeps a truncated read read-only without queuing a replacement", async () => {
     using _settings = setup();
diff --git a/apps/web/src/components/files/FilePreviewPanel.tsx b/apps/web/src/components/files/FilePreviewPanel.tsx
index 0311ce254ff4f..1461c3c3e4236 100644
--- a/apps/web/src/components/files/FilePreviewPanel.tsx
+++ b/apps/web/src/components/files/FilePreviewPanel.tsx
@@ -61,6 +61,7 @@ import { getLocalStorageItem, setLocalStorageItem, useLocalStorage } from "~/hoo
 import { resolveDiffThemeName } from "~/lib/diffRendering";
 import { PREFERRED_HIGHLIGHTER } from "~/lib/syntaxHighlighting";
 import { cn } from "~/lib/utils";
+import { requestWorkspaceFocus } from "~/lib/workspaceFocus";
 import type { ChatFileAttachment } from "~/types";
 import { isHostPath } from "@t3tools/shared/path";
 import { resolvePathLinkTarget } from "@t3tools/shared/fileLinks";
@@ -598,6 +599,7 @@ const createFileEditor: EditorFactory<FileCommentAnnotationGroup, undefined> = (
   options,
   editStateKey,
 ) => new Editor(editorType, options, editStateKey);
+type FileEditor = Editor<"file", FileCommentAnnotationGroup, undefined>;
 
 function editableFileContents(
   environmentId: EnvironmentId,
@@ -661,6 +663,7 @@ interface EditableFileSurfaceProps {
   wordWrap: boolean;
   onPostRender: FilePostRender;
   onPendingChange: (relativePath: string, pending: boolean) => void;
+  onEditorChange: (editor: FileEditor | null) => void;
 }
 
 interface FileSelectionOverride {
@@ -680,6 +683,7 @@ function EditableFileSurface({
   wordWrap,
   onPostRender,
   onPendingChange,
+  onEditorChange,
 }: EditableFileSurfaceProps) {
   const addReviewComment = useComposerDraftStore((store) => store.addReviewComment);
   const removeReviewComment = useComposerDraftStore((store) => store.removeReviewComment);
@@ -705,13 +709,15 @@ function EditableFileSurface({
   }
   const { ready: editable, onPostRender: onEditablePostRender } =
     useEditableAfterHighlight(externalFile);
-  const editorRef = useRef<Editor<"file", FileCommentAnnotationGroup, undefined> | null>(null);
+  const editorRef = useRef<FileEditor | null>(null);
   const editorOptions: EditorOptions<"file", FileCommentAnnotationGroup, undefined> = {
     onAttach: (editor) => {
       editorRef.current = editor;
+      onEditorChange(editor);
     },
     onComplete: () => {
       editorRef.current = null;
+      onEditorChange(null);
     },
   };
 
@@ -943,6 +949,7 @@ function RenderedMarkdownSurface({
   | "revealRequestId"
   | "wordWrap"
   | "onPostRender"
+  | "onEditorChange"
 > & {
   threadRef: ScopedThreadRef;
   readOnly: boolean;
@@ -1142,6 +1149,53 @@ export default function FilePreviewPanel({
     !(tableDelimiter && renderTable) &&
     !renderBrowserFile &&
     !isDocument;
+  const opensEditor =
+    previewPath !== null &&
+    !isHostFile &&
+    canWriteFiles &&
+    file.error === null &&
+    !file.data?.truncated &&
+    !isMedia &&
+    !isDocument &&
+    !renderBrowserFile &&
+    !renderMermaid &&
+    !(isMarkdown && renderMarkdown) &&
+    !(tableDelimiter && renderTable);
+  const editorFocusRef = useRef<HTMLDivElement>(null);
+  const fileEditorRef = useRef<FileEditor | null>(null);
+  const focusEditorFromPlaceholder = () => {
+    const editor = fileEditorRef.current;
+    if (!editor || document.activeElement !== editorFocusRef.current) return;
+    // Without a selection the editor focuses with no caret, and typing goes nowhere visible.
+    const hasCaret = Boolean(editor.getViewState().selections?.length);
+    editor.focus({
+      preventScroll: true,
+      ...(hasCaret ? {} : { lineNumber: revealLine ?? "first-visible" }),
+    });
+  };
+  const handleEditorChange = (editor: FileEditor | null) => {
+    fileEditorRef.current = editor;
+    focusEditorFromPlaceholder();
+  };
+  // Click and Enter open a file row; arrow keys also open files but keep browsing the tree.
+  const focusEditorFromTreeRow = (event: {
+    nativeEvent: Event;
+    altKey: boolean;
+    ctrlKey: boolean;
+    metaKey: boolean;
+    shiftKey: boolean;
+  }) => {
+    if (event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) return;
+    const row = event.nativeEvent
+      .composedPath()
+      .find(
+        (node): node is Element =>
+          node instanceof Element && node.matches('[role="treeitem"][data-item-path]'),
+      );
+    const path = row?.getAttribute("data-item-path");
+    if (!path || path.endsWith("/")) return;
+    requestWorkspaceFocus({ area: "panel", selector: "[data-file-content-focus]" });
+  };
   const rendered = isMermaid
     ? renderMermaid
     : isMarkdown
@@ -1360,10 +1414,30 @@ export default function FilePreviewPanel({
           Preview limited to the first 1 MB of a {file.data.byteLength.toLocaleString()} byte file.
         </div>
       ) : null}
-      <div className="flex min-h-0 flex-1 overflow-hidden">
+      <div
+        className="flex min-h-0 flex-1 overflow-hidden"
+        onClick={focusEditorFromTreeRow}
+        onKeyDown={(event) => {
+          if (event.key === "Enter") focusEditorFromTreeRow(event);
+        }}
+      >
         <div
           className={cn("min-w-0 flex-1 flex-col overflow-hidden", previewPath ? "flex" : "hidden")}
         >
+          {opensEditor ? (
+            // The editor lives in a shadow root and attaches after the file loads, so panel focus
+            // lands here and passes on once it can. sr-only keeps the box focus needs while clipping
+            // it from clicks. The hand-off waits a microtask: workspace focus checks focus stayed here.
+            <div
+              ref={editorFocusRef}
+              tabIndex={-1}
+              data-workspace-focus-default
+              data-file-content-focus
+              aria-label="File contents"
+              className="sr-only"
+              onFocus={() => queueMicrotask(focusEditorFromPlaceholder)}
+            />
+          ) : null}
           {isFolder ? null : relativePath && attachment ? (
             <AttachmentFilePreview
               key={`${environmentId}:${attachment.id}`}
@@ -1539,6 +1613,7 @@ export default function FilePreviewPanel({
                   wordWrap={wordWrap}
                   onPostRender={onFilePostRender}
                   onPendingChange={onPendingChange}
+                  onEditorChange={handleEditorChange}
                 />
               </DiffWorkerPoolProvider>
             )