fix: Open active file in external app instead of repo directory (#1470)

## Problem

Clicking "Open in [app]" always opened the repo root directory, even when a specific file was active in the editor.

<!-- Who is this for and what problem does it solve? -->

<!-- Closes #ISSUE_ID -->

## Changes

1. Derive active file path from panel layout store in TaskDetail
2. Join relative path with repo path as the external app target, fall back to repo directory
3. Add fixed overlay to prevent drag-through when dropdown menu is open
4. Fix dead diff type check and normalize path joining

<!-- What did you change and why? -->

<!-- If there are frontend changes, include screenshots. -->

## How did you test this?

Manually

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Author: charlesvien

apps/code/src/renderer/features/task-detail/components/ExternalAppsOpener.tsx

@@ -4,7 +4,7 @@ import { ChevronDownIcon } from "@radix-ui/react-icons";
 import { Button, DropdownMenu, Flex, Text } from "@radix-ui/themes";
 import { SHORTCUTS } from "@renderer/constants/keyboard-shortcuts";
 import { handleExternalAppAction } from "@utils/handleExternalAppAction";
-import { useCallback } from "react";
+import { useCallback, useState } from "react";
 import { useHotkeys } from "react-hotkeys-hook";
 
 const THUMBNAIL_ICON_SIZE = 20;
@@ -20,6 +20,7 @@ export function ExternalAppsOpener({
   label = "Open",
 }: ExternalAppsOpenerProps) {
   const { detectedApps, defaultApp, isLoading } = useExternalApps();
+  const [dropdownOpen, setDropdownOpen] = useState(false);
 
   const handleOpenDefault = useCallback(async () => {
     if (!defaultApp || !targetPath) return;
@@ -81,7 +82,17 @@ export function ExternalAppsOpener({
   const isReady = !isLoading && detectedApps.length > 0;
 
   return (
-    <DropdownMenu.Root>
+    <DropdownMenu.Root open={dropdownOpen} onOpenChange={setDropdownOpen}>
+      {dropdownOpen && (
+        <div
+          className="no-drag"
+          style={{
+            position: "fixed",
+            inset: 0,
+            zIndex: 1,
+          }}
+        />
+      )}
       <Flex className="no-drag">
         <Button
           size="1"

apps/code/src/renderer/features/task-detail/components/TaskDetail.tsx

@@ -1,5 +1,10 @@
 import { FilePicker } from "@features/command/components/FilePicker";
 import { PanelLayout } from "@features/panels";
+import { usePanelLayoutStore } from "@features/panels/store/panelLayoutStore";
+import {
+  getLeafPanel,
+  parseTabId,
+} from "@features/panels/store/panelStoreHelpers";
 import { useCwd } from "@features/sidebar/hooks/useCwd";
 import { useTaskData } from "@features/task-detail/hooks/useTaskData";
 import { useTaskStore } from "@features/tasks/stores/taskStore";
@@ -30,6 +35,28 @@ export function TaskDetail({ task: initialTask }: TaskDetailProps) {
 
   const effectiveRepoPath = useCwd(taskId);
 
+  const activeRelativePath = usePanelLayoutStore((state) => {
+    const layout = state.getLayout(taskId);
+    if (!layout) return null;
+
+    const panelId = layout.focusedPanelId;
+    if (!panelId) return null;
+
+    const panel = getLeafPanel(layout.panelTree, panelId);
+    if (!panel) return null;
+
+    const parsed = parseTabId(panel.content.activeTabId);
+    if (parsed.type === "file") {
+      return parsed.value;
+    }
+    return null;
+  });
+
+  const openTargetPath =
+    activeRelativePath && effectiveRepoPath
+      ? [effectiveRepoPath, activeRelativePath].join("/").replace(/\/+/g, "/")
+      : effectiveRepoPath;
+
   const [filePickerOpen, setFilePickerOpen] = useState(false);
 
   const { enableScope, disableScope } = useHotkeysContext();
@@ -60,12 +87,10 @@ export function TaskDetail({ task: initialTask }: TaskDetailProps) {
             {task.title}
           </Text>
         </Flex>
-        {effectiveRepoPath && (
-          <ExternalAppsOpener targetPath={effectiveRepoPath} />
-        )}
+        {openTargetPath && <ExternalAppsOpener targetPath={openTargetPath} />}
       </Flex>
     ),
-    [task.title, effectiveRepoPath],
+    [task.title, openTargetPath],
   );
 
   useSetHeaderContent(headerContent);