feat(core): allow reusing existing worktrees with --worktree flag

docs/cli/git-worktrees.md

@@ -80,8 +80,23 @@ manually remove the worktree if you no longer need it.
 
 ## Resuming work in a Git worktree
 
-To resume a session in a worktree, navigate to the worktree directory and start
-Gemini CLI with the `--resume` flag and the session ID:
+To resume a session in an existing worktree, you can simply run Gemini with the
+same `--worktree` (`-w`) name:
+
+```bash
+gemini --worktree feature-search
+```
+
+Alternatively, you can navigate to the worktree directory and start Gemini
+directly:
+
+```bash
+cd .gemini/worktrees/feature-search
+gemini
+```
+
+To resume a specific previous chat session within that worktree, use the
+`--resume` flag and the session ID:
 
 ```bash
 cd .gemini/worktrees/feature-search

packages/core/src/services/worktreeService.test.ts

@@ -85,7 +85,8 @@ describe('worktree utilities', () => {
   });
 
   describe('createWorktree', () => {
-    it('should execute git worktree add with correct branch and path', async () => {
+    it('should execute git worktree add with correct branch and path if it does not exist', async () => {
+      vi.mocked(fs.access).mockRejectedValue(new Error('ENOENT'));
       vi.mocked(execa).mockResolvedValue({ stdout: '' } as never);
 
       const resultPath = await createWorktree(projectRoot, worktreeName);
@@ -98,7 +99,17 @@ describe('worktree utilities', () => {
       );
     });
 
+    it('should return existing path and not call git if it already exists', async () => {
+      vi.mocked(fs.access).mockResolvedValue(undefined);
+
+      const resultPath = await createWorktree(projectRoot, worktreeName);
+
+      expect(resultPath).toBe(expectedPath);
+      expect(execa).not.toHaveBeenCalled();
+    });
+
     it('should throw an error if git worktree add fails', async () => {
+      vi.mocked(fs.access).mockRejectedValue(new Error('ENOENT'));
       vi.mocked(execa).mockRejectedValue(new Error('git failed'));
 
       await expect(createWorktree(projectRoot, worktreeName)).rejects.toThrow(

packages/core/src/services/worktreeService.ts

@@ -120,6 +120,15 @@ export async function createWorktree(
   name: string,
 ): Promise<string> {
   const worktreePath = getWorktreePath(projectRoot, name);
+
+  try {
+    await fs.access(worktreePath);
+    // Worktree path already exists, reuse it
+    return worktreePath;
+  } catch {
+    // Does not exist, proceed to create
+  }
+
   const branchName = `worktree-${name}`;
 
   await execa('git', ['worktree', 'add', worktreePath, '-b', branchName], {