fix(app): reuse file tabs opened from nested-project Changes

Changes paths are relative to the current worktree. Resolve file actions
from that root, then give file tabs and chat attachments the existing
workspace-relative target for files inside the project. Keep absolute
targets for changed files outside it so both paths remain addressable.

The contributor's root-path fix opened inside-project files with absolute
targets, which differed from Files and created duplicate retained tabs.
A failing-first browser journey covers navigation between both views.

Co-authored-by: 3ae3ae <ogyshjsm@naver.com>

packages/app/e2e/browser/changes-pane.spec.ts

@@ -8,6 +8,7 @@ import { daemonWsRoutePattern } from "../support/helpers/daemon-port";
 import { getServerId } from "../support/helpers/server-id";
 import { connectSeedClient } from "../support/helpers/seed-client";
 import { createTempGitRepo } from "../support/helpers/workspace";
+import { openFileExplorer, openFileFromExplorer } from "../support/helpers/file-explorer";
 import { openChangesPanel, waitForWorkspaceTabsVisible } from "../support/helpers/workspace-tabs";
 
 interface DirtyWorkspace {
@@ -506,6 +507,44 @@ for (const { workspaceSubdirectory, filePath, content, visibleContent } of [
   });
 }
 
+test("Changes and Files reuse a retained file tab in a subfolder project", async ({ page }) => {
+  const workspace = await createWorkspaceWithMountedTabDiff({ workspaceSubdirectory: "src" });
+  await openWorkspaceChanges(page, workspace);
+  await openChangedFile(page, "src/use-mounted-tab-set.ts");
+  await editAndSaveChangedFile(page, workspace);
+  await openChangesPanel(page);
+  await openFileExplorer(page);
+  await openFileFromExplorer(page, "use-mounted-tab-set.ts");
+
+  await expect(page.getByTestId(/^workspace-tab-file_/).filter({ visible: true })).toHaveCount(1);
+  await expect(page.getByTestId("workspace-tab-file_use-mounted-tab-set.ts")).toHaveAttribute(
+    "aria-selected",
+    "true",
+  );
+  await expect(visibleFileEditor(page)).toContainText("// retained file tab");
+});
+
+async function openChangedFile(page: Page, filePath: string): Promise<void> {
+  const panel = page.getByTestId("working-diff-panel").filter({ visible: true });
+  await diffHeaderForPath(panel, filePath)
+    .getByTestId(/^diff-file-\d+-toggle$/)
+    .click({ button: "right" });
+  await page.getByRole("menuitem", { name: "Open file", exact: true }).click();
+  await expect(visibleFileEditor(page)).toContainText("interface DeriveRenderMountedTabIdsInput");
+}
+
+function visibleFileEditor(page: Page): Locator {
+  return page.getByTestId("workspace-file-pane").filter({ visible: true }).locator(".cm-content");
+}
+
+async function editAndSaveChangedFile(page: Page, workspace: DirtyWorkspace): Promise<void> {
+  const content = "// retained file tab\n" + AFTER;
+  await visibleFileEditor(page).fill(content);
+  await expect
+    .poll(() => readFile(path.join(workspace.repoPath, "src/use-mounted-tab-set.ts"), "utf8"))
+    .toBe(content);
+}
+
 test("canvas file headers select without toggling for context menu and long press", async ({
   page,
 }) => {

packages/app/src/git/diff-pane.tsx

@@ -56,7 +56,7 @@ import * as Clipboard from "expo-clipboard";
 import { useFileDownload } from "@/hooks/use-file-download";
 import { useIsLocalDaemon } from "@/hooks/use-is-local-daemon";
 import { buildAbsoluteExplorerPath } from "@/utils/explorer-paths";
-import { isWorkspaceRootPath } from "@/workspace/file-open";
+import { resolveWorkspaceFilePaths } from "@/workspace/file-open";
 import { Tooltip, TooltipTrigger, TooltipContent } from "@/components/ui/tooltip";
 import { GitActionsSplitButton } from "@/git/actions-split-button";
 import type { GitActions } from "@/git/policy";
@@ -1637,14 +1637,17 @@ export function ChangesSurface({
     [appSettings.monoFontFamily, codeFontSize, effectiveLayout, wrapLines],
   );
   const fileRoot = resolveChangesFileRoot(status, cwd);
-  const isRootWorkspace = isWorkspaceRootPath({ path: fileRoot, workspaceRoot: cwd });
   const resolveFilePath = useCallback(
     (path: string) => buildAbsoluteExplorerPath({ workspaceRoot: fileRoot, entryPath: path }),
     [fileRoot],
   );
   const resolveFileTargetPath = useCallback(
-    (path: string) => (isRootWorkspace ? path : resolveFilePath(path)),
-    [isRootWorkspace, resolveFilePath],
+    (path: string) => {
+      const absolutePath = resolveFilePath(path);
+      const resolved = resolveWorkspaceFilePaths({ path: absolutePath, workspaceRoot: cwd });
+      return resolved?.relativePath ?? absolutePath;
+    },
+    [cwd, resolveFilePath],
   );
   const handleOpenFile = useCallback(
     (path: string) => onOpenFile?.(resolveFileTargetPath(path)),