diff --git a/packages/ui/src/components/session/GitHubIntegrationDialog.tsx b/packages/ui/src/components/session/GitHubIntegrationDialog.tsx
index 0deacae2..e80b537a 100644
--- a/packages/ui/src/components/session/GitHubIntegrationDialog.tsx
+++ b/packages/ui/src/components/session/GitHubIntegrationDialog.tsx
@@ -195,13 +195,15 @@ export function GitHubIntegrationDialog({
         worktreeName: branchName,
       });
       
-      const isBlocked = result.errors.some(
-        (entry) => entry.code === 'branch_in_use' || entry.code === 'branch_exists'
-      );
+      const blockingError = result.errors.find((entry) => entry.code === 'branch_in_use');
       
       setValidations(prev => new Map(prev).set(branchName, {
-        isValid: !isBlocked,
-        error: isBlocked ? t('session.githubIntegration.validation.branchAlreadyCheckedOut') : null,
+        isValid: !blockingError,
+        error: blockingError
+          ? t(blockingError.code === 'branch_exists'
+            ? 'session.githubIntegration.validation.branchAlreadyExists'
+            : 'session.githubIntegration.validation.branchAlreadyCheckedOut')
+          : null,
       }));
     } catch {
       setValidations(prev => new Map(prev).set(branchName, {
diff --git a/packages/ui/src/components/session/NewWorktreeDialog.tsx b/packages/ui/src/components/session/NewWorktreeDialog.tsx
index 90f271d5..15bff4f4 100644
--- a/packages/ui/src/components/session/NewWorktreeDialog.tsx
+++ b/packages/ui/src/components/session/NewWorktreeDialog.tsx
@@ -129,12 +129,24 @@ const sanitizeRemoteName = (value: string): string => {
   return normalized || 'pr-head';
 };
 
-const resolvePrWorktreeConfig = (pr: GitHubPullRequestSummary, remoteBranches: string[]) => {
+const resolvePrWorktreeConfig = (pr: GitHubPullRequestSummary, localBranches: string[], remoteBranches: string[]) => {
   const headBranch = normalizeBranchName(pr.head || '');
   if (!headBranch) {
     throw new Error('PR head branch is missing');
   }
 
+  if (localBranches.includes(headBranch)) {
+    return {
+      existingBranch: headBranch,
+      setUpstream: undefined,
+      upstreamRemote: undefined,
+      upstreamBranch: undefined,
+      ensureRemoteName: undefined,
+      ensureRemoteUrl: undefined,
+      sourceLabel: headBranch,
+    };
+  }
+
   const availableRemoteBranch = remoteBranches.find((remoteBranch) => {
     const slashIndex = remoteBranch.indexOf('/');
     if (slashIndex <= 0 || slashIndex >= remoteBranch.length - 1) {
@@ -734,11 +746,15 @@ export function NewWorktreeDialog({
       
       // Only run server validation if we have values
       if (normalizedBranch && normalizedWorktree) {
+        const linkedPr = mode === 'new-branch' ? newBranchState.linkedPr : null;
+        const prConfig = linkedPr ? resolvePrWorktreeConfig(linkedPr, localBranches, remoteBranches) : null;
         const result = await validateWorktreeCreate(projectRef, {
-          mode: mode === 'existing-branch' ? 'existing' : 'new',
+          mode: mode === 'existing-branch' || prConfig ? 'existing' : 'new',
           branchName: normalizedBranch,
           worktreeName: normalizedWorktree,
-          existingBranch: mode === 'existing-branch' ? normalizedBranch : undefined,
+          existingBranch: prConfig?.existingBranch ?? (mode === 'existing-branch' ? normalizedBranch : undefined),
+          ...(prConfig?.ensureRemoteName ? { ensureRemoteName: prConfig.ensureRemoteName } : {}),
+          ...(prConfig?.ensureRemoteUrl ? { ensureRemoteUrl: prConfig.ensureRemoteUrl } : {}),
         });
         
         if (abortController.signal.aborted) return;
@@ -777,8 +793,11 @@ export function NewWorktreeDialog({
     projectRef,
     mode,
     newBranchState.branchName,
+    newBranchState.linkedPr,
     existingBranchState.selectedBranch,
     currentState.worktreeName,
+    localBranches,
+    remoteBranches,
     validation.touched,
     validationAbortController,
     isCreating,
@@ -846,7 +865,7 @@ export function NewWorktreeDialog({
       let sourceLabel = '';
       const args = (() => {
         if (linkedPr) {
-          const prConfig = resolvePrWorktreeConfig(linkedPr, remoteBranches);
+          const prConfig = resolvePrWorktreeConfig(linkedPr, localBranches, remoteBranches);
           sourceLabel = prConfig.sourceLabel;
           return {
             preferredName: normalizedBranch || normalizedWorktree,
diff --git a/packages/ui/src/lib/i18n/messages/en.ts b/packages/ui/src/lib/i18n/messages/en.ts
index c353d00c..d37cf241 100644
--- a/packages/ui/src/lib/i18n/messages/en.ts
+++ b/packages/ui/src/lib/i18n/messages/en.ts
@@ -1323,6 +1323,7 @@ export const dict = {
   'session.githubIntegration.error.notConnected': 'GitHub not connected',
   'session.githubIntegration.error.loadDataFailed': 'Failed to load data',
   'session.githubIntegration.validation.branchAlreadyCheckedOut': 'Branch is already checked out in a worktree',
+  'session.githubIntegration.validation.branchAlreadyExists': 'Branch already exists locally',
   'session.githubIntegration.validation.failed': 'Validation failed',
   'chat.fileAttachment.toast.attachFailed': 'Failed to attach file',
   'chat.fileAttachment.toast.someFilesSkipped': 'Some files were skipped:\n{summary}',
diff --git a/packages/ui/src/lib/i18n/messages/es.ts b/packages/ui/src/lib/i18n/messages/es.ts
index 4ae14555..e975342f 100644
--- a/packages/ui/src/lib/i18n/messages/es.ts
+++ b/packages/ui/src/lib/i18n/messages/es.ts
@@ -1289,6 +1289,7 @@ export const dict: Record<I18nKey, string> = {
   "session.githubIntegration.error.notConnected": "GitHub no está conectado",
   "session.githubIntegration.error.loadDataFailed": "No se pudieron cargar los datos",
   "session.githubIntegration.validation.branchAlreadyCheckedOut": "La rama ya está en uso en un worktree",
+  "session.githubIntegration.validation.branchAlreadyExists": "La rama ya existe localmente",
   "session.githubIntegration.validation.failed": "No se pudo validar",
   "chat.fileAttachment.toast.attachFailed": "No se pudo adjuntar el archivo",
   "chat.fileAttachment.toast.someFilesSkipped": "Algunos archivos se omitieron:\n{summary}",
diff --git a/packages/ui/src/lib/i18n/messages/ko.ts b/packages/ui/src/lib/i18n/messages/ko.ts
index dee46a18..5dc7c9e7 100644
--- a/packages/ui/src/lib/i18n/messages/ko.ts
+++ b/packages/ui/src/lib/i18n/messages/ko.ts
@@ -1325,6 +1325,7 @@ export const dict: Record<I18nKey, string> = {
   'session.githubIntegration.error.notConnected': 'GitHub에 연결되어 있지 않습니다',
   'session.githubIntegration.error.loadDataFailed': '데이터를 불러오지 못했습니다',
   'session.githubIntegration.validation.branchAlreadyCheckedOut': '브랜치가 이미 워크트리에 체크아웃되어 있습니다',
+  'session.githubIntegration.validation.branchAlreadyExists': '브랜치가 이미 로컬에 있습니다',
   'session.githubIntegration.validation.failed': '유효성 검사에 실패했습니다',
   'chat.fileAttachment.toast.attachFailed': '첨부 파일 실패',
   'chat.fileAttachment.toast.someFilesSkipped': '일부 파일을 건너뛰었습니다:\n{summary}',
diff --git a/packages/ui/src/lib/i18n/messages/pl.ts b/packages/ui/src/lib/i18n/messages/pl.ts
index 9ac6c423..f542017e 100644
--- a/packages/ui/src/lib/i18n/messages/pl.ts
+++ b/packages/ui/src/lib/i18n/messages/pl.ts
@@ -390,6 +390,7 @@ export const dict: Record<I18nKey, string> = {
   'session.githubIntegration.error.notConnected': 'GitHub nie jest połączony',
   'session.githubIntegration.error.loadDataFailed': 'Nie udało się załadować danych',
   'session.githubIntegration.validation.branchAlreadyCheckedOut': 'Gałąź jest już wyewidencjonowana w drzewie pracy',
+  'session.githubIntegration.validation.branchAlreadyExists': 'Gałąź już istnieje lokalnie',
   'session.githubIntegration.validation.failed': 'Walidacja nie powiodła się',
   'chat.fileAttachment.toast.attachFailed': 'Nie udało się dołączyć pliku',
   'chat.fileAttachment.toast.someFilesSkipped': 'Niektóre pliki zostały pominięte:\n{summary}',
diff --git a/packages/ui/src/lib/i18n/messages/pt-BR.ts b/packages/ui/src/lib/i18n/messages/pt-BR.ts
index 366a1262..5a4a5da0 100644
--- a/packages/ui/src/lib/i18n/messages/pt-BR.ts
+++ b/packages/ui/src/lib/i18n/messages/pt-BR.ts
@@ -1289,6 +1289,7 @@ export const dict: Record<I18nKey, string> = {
   "session.githubIntegration.error.notConnected": "GitHub não está conectado",
   "session.githubIntegration.error.loadDataFailed": "Não foi possível carregar os dados",
   "session.githubIntegration.validation.branchAlreadyCheckedOut": "A branch já está em uso em um worktree",
+  "session.githubIntegration.validation.branchAlreadyExists": "A branch já existe localmente",
   "session.githubIntegration.validation.failed": "Não foi possível validar",
   "chat.fileAttachment.toast.attachFailed": "Não foi possível anexar o arquivo",
   "chat.fileAttachment.toast.someFilesSkipped": "Alguns arquivos foram omitidos:\n{summary}",
diff --git a/packages/ui/src/lib/i18n/messages/uk.ts b/packages/ui/src/lib/i18n/messages/uk.ts
index 23bd7f04..d2258504 100644
--- a/packages/ui/src/lib/i18n/messages/uk.ts
+++ b/packages/ui/src/lib/i18n/messages/uk.ts
@@ -1289,6 +1289,7 @@ export const dict: Record<I18nKey, string> = {
   "session.githubIntegration.error.notConnected": "GitHub не підключено",
   "session.githubIntegration.error.loadDataFailed": "Не вдалося завантажити дані",
   "session.githubIntegration.validation.branchAlreadyCheckedOut": "Гілку вже відкрито в worktree",
+  "session.githubIntegration.validation.branchAlreadyExists": "Гілка вже існує локально",
   "session.githubIntegration.validation.failed": "Помилка перевірки",
   "chat.fileAttachment.toast.attachFailed": "Не вдалося прикріпити файл",
   "chat.fileAttachment.toast.someFilesSkipped": "Деякі файли були пропущені:\n{summary}",
diff --git a/packages/ui/src/lib/i18n/messages/zh-CN.ts b/packages/ui/src/lib/i18n/messages/zh-CN.ts
index e121369b..9772183b 100644
--- a/packages/ui/src/lib/i18n/messages/zh-CN.ts
+++ b/packages/ui/src/lib/i18n/messages/zh-CN.ts
@@ -1289,6 +1289,7 @@ export const dict: Record<I18nKey, string> = {
   'session.githubIntegration.error.notConnected': 'GitHub 未连接',
   'session.githubIntegration.error.loadDataFailed': '加载数据失败',
   'session.githubIntegration.validation.branchAlreadyCheckedOut': '该分支已在某个 worktree 中检出',
+  'session.githubIntegration.validation.branchAlreadyExists': '该分支已在本地存在',
   'session.githubIntegration.validation.failed': '校验失败',
   'chat.fileAttachment.toast.attachFailed': '附加文件失败',
   'chat.fileAttachment.toast.someFilesSkipped': '以下文件被跳过：\n{summary}',