fix(app): route workspace actions semantically (#3896)

* fix(app): route workspace actions semantically

Separate Explorer visibility from view navigation, and give composer changes and pull request opens semantic routing owners. Unify diff destinations, keep compact PR navigation in Explorer, and derive maximize availability from visible workspace panes.

* test(app): cover composer changes routing

Update the browser journey for the Explorer-first composer action, then assert the second press follows the shared diff destination.

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

@@ -102,8 +102,8 @@ import { DiffTooLargeState } from "@/git/diff-too-large-state";
 import { openDesktopTarget, useDesktopOpenTargets } from "@/workspace/desktop-open-targets";
 import { PullRequestStateIcon } from "@/git/pull-request-state-icon";
 import { openExternalUrl } from "@/utils/open-external-url";
-import { openWorkspaceSupportingView } from "@/workspace-tabs/open-supporting-view";
-import type { OpenInSidePanePreferences } from "@/hooks/use-settings";
+import { openWorkspacePullRequest } from "@/workspace-tabs/open-supporting-view";
+import type { PullRequestOpenLocation } from "@/hooks/use-settings";
 
 export type { GitActionId, GitAction, GitActions } from "@/git/policy";
 
@@ -1511,13 +1511,13 @@ function useDiffTabNavigation({
   workspaceId,
   cwd,
   isMobile,
-  openInSidePane,
+  pullRequestOpenLocation,
 }: {
   serverId: string;
   workspaceId?: string | null;
   cwd: string;
   isMobile: boolean;
-  openInSidePane: OpenInSidePanePreferences;
+  pullRequestOpenLocation: PullRequestOpenLocation;
 }) {
   const openTab = useWorkspaceLayoutStore((state) => state.openTab);
   const openWorkspaceTab = useCallback(
@@ -1545,14 +1545,13 @@ function useDiffTabNavigation({
   );
   const openPullRequest = useCallback(() => {
     if (!persistenceKey) return;
-    openWorkspaceSupportingView({
-      view: "pull-request",
+    openWorkspacePullRequest({
       isCompact: isMobile,
       workspaceKey: persistenceKey,
       checkout: { serverId, cwd, isGit: true },
-      preferences: openInSidePane,
+      destination: pullRequestOpenLocation,
     });
-  }, [cwd, isMobile, openInSidePane, persistenceKey, serverId]);
+  }, [cwd, isMobile, persistenceKey, pullRequestOpenLocation, serverId]);
   return {
     openDiff,
     openCommit,
@@ -1633,7 +1632,7 @@ export function ChangesSurface({
     workspaceId,
     cwd,
     isMobile,
-    openInSidePane: appSettings.openInSidePane,
+    pullRequestOpenLocation: appSettings.pullRequestOpenLocation,
   });
   const refreshSupported = useSessionStore(
     (s) => s.sessions[serverId]?.serverInfo?.features?.checkoutRefresh === true,