fix(git): exit nested-repo states once resolution succeeds

NestedRepoResolutionStates had no success exit: on a non-repo root
rootIsGitRepo stays false forever, so once repositories were found the
pull-request and walkthrough tabs kept showing 'Checking repository'
even after the selected repository probed as a repository. GitView never
hit this because its call site sits inside its own isGitRepo === false
branch. The component now takes the operating directory's probe and
returns null when it resolves true.

DiffView also still keyed its not-a-repository gate and every diff
fetch off the raw project root, so opening a change from a nested
repository showed 'This directory is not a Git repository'. It now
resolves the nested repository for git data and diff operations while
session-scoped lookups (session messages, review-flow directory) stay
on the root.

packages/ui/src/apps/MobileChangesSurface.tsx

@@ -487,6 +487,7 @@ export const MobileChangesSurface: React.FC<MobileChangesSurfaceProps> = ({ onCl
     return renderListState(
       <NestedRepoResolutionStates
         rootIsGitRepo={rootIsGitRepo}
+        resolvedIsGitRepo={isGitRepo}
         nestedRepos={nestedRepos}
         onRetryDiscovery={() => {
           if (rootDirectory) void ensureNestedRepos(rootDirectory, { force: true });

packages/ui/src/components/views/DiffView.tsx

@@ -2,6 +2,7 @@ import React from 'react';
 
 import { useUIStore } from '@/stores/useUIStore';
 import { useEffectiveDirectory } from '@/hooks/useEffectiveDirectory';
+import { useNestedGitDirectory } from '@/hooks/useNestedGitDirectory';
 import { useGitStore, useGitStatus, useIsGitRepo, useGitLoadingStatus } from '@/stores/useGitStore';
 import { useGitBaseBranchStore, gitBaseBranchEntryKey } from '@/stores/useGitBaseBranchStore';
 import { coerceDiffScope, branchRangeKey, isBranchScopeAvailable, isBranchScopeDefinitelyUnavailable, useRangeKeyedCache, useBoundedDirectoryRetry } from './branchDiffScope';
@@ -997,7 +998,11 @@ export const DiffView: React.FC<DiffViewProps> = ({
 }) => {
     const { t } = useI18n();
     const { git, files } = useRuntimeAPIs();
-    const effectiveDirectory = useEffectiveDirectory();
+    const rootDirectory = useEffectiveDirectory();
+    // Diffs belong to the repository being diffed: when the root is not
+    // itself a repository, operate on the resolved nested repository instead.
+    const { gitDirectory: nestedGitDirectory } = useNestedGitDirectory(rootDirectory ?? null);
+    const effectiveDirectory = nestedGitDirectory ?? rootDirectory;
     const openContextSurface = useUIStore((state) => state.openContextSurface);
     const requestWalkthroughSource = useWalkthroughStore((state) => state.requestSource);
     const { screenWidth, isMobile } = useDeviceInfo();
@@ -1038,7 +1043,7 @@ export const DiffView: React.FC<DiffViewProps> = ({
     const setDiffWrapLines = useUIStore((state) => state.setDiffWrapLines);
     const openContextFileAtLine = useUIStore((state) => state.openContextFileAtLine);
     const currentSessionId = useSessionUIStore((state) => state.currentSessionId);
-    const sessionMessages = useSessionMessages(currentSessionId ?? '', effectiveDirectory ?? undefined);
+    const sessionMessages = useSessionMessages(currentSessionId ?? '', rootDirectory ?? undefined);
     const diffWrapLines = diffWrapLinesStore;
     const forcedStaged = activeDiffScope === 'staged' ? true : activeDiffScope === 'working' ? false : null;
     const activeDiffStaged = forcedStaged ?? displayFileStaged;
@@ -1645,7 +1650,7 @@ export const DiffView: React.FC<DiffViewProps> = ({
 
     const handleStartReviewFlow = React.useCallback(async (execution: ReviewFlowExecution) => {
         if (!currentSessionId) return;
-        const directory = useSessionUIStore.getState().getDirectoryForSession(currentSessionId) || effectiveDirectory || '';
+        const directory = useSessionUIStore.getState().getDirectoryForSession(currentSessionId) || rootDirectory || '';
         if (!directory) {
             toast.error(t('diffView.reviewDialog.toast.noSessionDirectory'));
             return;

packages/ui/src/components/views/GitView.tsx

@@ -2343,6 +2343,7 @@ export const GitView: React.FC<GitViewProps> = ({ isActive }) => {
     return (
       <NestedRepoResolutionStates
         rootIsGitRepo={rootIsGitRepo}
+        resolvedIsGitRepo={isGitRepo}
         nestedRepos={nestedRepos}
         onRetryDiscovery={() => {
           if (currentDirectory) {

packages/ui/src/components/views/PullRequestView.tsx

@@ -265,6 +265,7 @@ export const PullRequestView: React.FC = () => {
     return (
       <NestedRepoResolutionStates
         rootIsGitRepo={rootIsGitRepo}
+        resolvedIsGitRepo={isGitRepo}
         nestedRepos={nestedRepos}
         onRetryDiscovery={() => {
           void ensureNestedRepos(currentDirectory, { force: true });

packages/ui/src/components/views/git/NestedRepoResolutionStates.tsx

@@ -8,6 +8,12 @@ import type { NestedRepoDiscovery } from '@/stores/useGitStore';
 type NestedRepoResolutionStatesProps = {
   /** Probe of the project root: `false` means nested resolution applies. */
   rootIsGitRepo: boolean | null;
+  /**
+   * Probe of the directory the consumer operates on (root or selected nested
+   * repository). `true` means resolution succeeded and the consumer should
+   * render its own content.
+   */
+  resolvedIsGitRepo: boolean | null;
   /** Discovery outcome for the root (`undefined` = not run yet). */
   nestedRepos: NestedRepoDiscovery | undefined;
   onRetryDiscovery: () => void;
@@ -17,8 +23,9 @@ type NestedRepoResolutionStatesProps = {
 
 /**
  * Shared empty/loading states for git surfaces while nested-repository
- * resolution is pending, failed, or impossible. Renders null once
+ * resolution is pending, failed, or impossible. Renders null once resolution
- * repositories are resolved so the consumer can proceed into its own content.
+ * has finished — either the root is a repository or the operating directory
+ * probed as one — so the consumer can proceed into its own content.
  *
  * A runtime without the discovery route (VS Code) reports "unsupported": the
  * honest state there is the plain not-a-repository empty state, without a
@@ -26,6 +33,7 @@ type NestedRepoResolutionStatesProps = {
  */
 export const NestedRepoResolutionStates: React.FC<NestedRepoResolutionStatesProps> = ({
   rootIsGitRepo,
+  resolvedIsGitRepo,
   nestedRepos,
   onRetryDiscovery,
   emptyStateFooter,
@@ -33,6 +41,7 @@ export const NestedRepoResolutionStates: React.FC<NestedRepoResolutionStatesProp
   const { t } = useI18n();
 
   if (rootIsGitRepo !== false) return null;
+  if (resolvedIsGitRepo === true) return null;
 
   if (nestedRepos === undefined || nestedRepos === null) {
     return (

packages/ui/src/components/views/walkthrough/WalkthroughView.tsx

@@ -498,6 +498,7 @@ export const WalkthroughView = ({ directory: rootDirectory }: WalkthroughViewPro
     return (
       <NestedRepoResolutionStates
         rootIsGitRepo={rootIsGitRepo}
+        resolvedIsGitRepo={isGitRepo}
         nestedRepos={nestedRepos}
         onRetryDiscovery={() => {
           if (rootDirectory) void ensureNestedRepos(rootDirectory, { force: true });