fix(dev): always warn when creating worktree on existing branch

agent_cli/dev/worktree.py

@@ -662,13 +662,19 @@ def create_worktree(
     # Check if branch exists remotely or locally
     remote_exists, local_exists = check_branch_exists(branch_name, repo_root)
 
-    # Generate warning if --from was specified but will be ignored
+    # Generate warning when the branch already exists
     warning: str | None = None
-    if from_ref_explicit and (local_exists or remote_exists):
-        warning = (
-            f"Branch '{branch_name}' already exists. "
-            f"Using existing branch instead of creating from '{from_ref}'."
-        )
+    if local_exists or remote_exists:
+        if from_ref_explicit:
+            warning = (
+                f"Branch '{branch_name}' already exists. "
+                f"Using existing branch instead of creating from '{from_ref}'."
+            )
+        else:
+            warning = (
+                f"Branch '{branch_name}' already exists. "
+                f"Using existing branch (use a different name to start fresh)."
+            )
 
     try:
         _add_worktree(

tests/dev/test_worktree.py

@@ -496,8 +496,8 @@ def test_warning_when_remote_branch_exists_and_from_specified(self) -> None:
             assert result.warning is not None
             assert "already exists" in result.warning
 
-    def test_no_warning_when_from_not_specified(self) -> None:
-        """No warning when --from is not specified (uses default)."""
+    def test_warning_when_from_not_specified_but_branch_exists(self) -> None:
+        """Warning shown when branch exists even without explicit --from."""
         with (
             patch("agent_cli.dev.worktree.get_main_repo_root", return_value=Path("/repo")),
             patch(
@@ -523,7 +523,9 @@ def test_no_warning_when_from_not_specified(self) -> None:
             )
 
             assert result.success is True
-            assert result.warning is None  # No warning since --from wasn't explicit
+            assert result.warning is not None
+            assert "already exists" in result.warning
+            assert "use a different name" in result.warning.lower()
 
     def test_no_warning_when_branch_is_new(self) -> None:
         """No warning when branch doesn't exist (will be created from --from)."""