feat: emit init-time notice for git extension default change (#2165) (#2432)

Add a non-blocking Panel notice during `specify init` when the git
extension auto-enables, informing users that starting in v0.10.0 this
will require explicit opt-in via `specify extension add git`.

- src/specify_cli/__init__.py: track successful git extension install
  and display yellow "Notice: Git Default Changing" panel
- tests/integrations/test_cli.py: integration test validating notice
  content (v0.10.0 timeline, opt-in messaging, migration command)
- docs/reference/core.md: user-facing NOTE about the upcoming change

Closes #2165

docs/reference/core.md

@@ -22,6 +22,10 @@ specify init [<project_name>]
 
 Creates a new Spec Kit project with the necessary directory structure, templates, scripts, and AI coding agent integration files.
 
+> [!NOTE]
+> The git extension is currently enabled by default during `specify init`.
+> Starting in `v0.10.0`, it will require explicit opt-in. To add it after init, run `specify extension add git`.
+
 Use `<project_name>` to create a new directory, or `--here` (or `.`) to initialize in the current directory. If the directory already has files, use `--force` to merge without confirmation.
 
 ### Examples

src/specify_cli/__init__.py

@@ -1264,6 +1264,8 @@ def init(
     ]:
         tracker.add(key, label)
 
+    git_default_notice = False
+
     with Live(tracker.render(), console=console, refresh_per_second=8, transient=True) as live:
         tracker.attach_refresh(lambda: live.update(tracker.render()))
         try:
@@ -1360,6 +1362,7 @@ def init(
                             manager.install_from_directory(
                                 bundled_path, get_speckit_version()
                             )
+                            git_default_notice = True
                             git_messages.append("extension installed")
                     else:
                         git_has_error = True
@@ -1530,6 +1533,18 @@ def init(
         console.print()
         console.print(deprecation_notice)
 
+    if git_default_notice:
+        default_change_notice = Panel(
+            "The git extension is currently enabled by default during [bold]specify init[/bold].\n"
+            "Starting in [bold]v0.10.0[/bold], this will require explicit opt-in.\n"
+            "Use [bold]specify extension add git[/bold] after init when needed.",
+            title="[yellow]Notice: Git Default Changing[/yellow]",
+            border_style="yellow",
+            padding=(1, 2),
+        )
+        console.print()
+        console.print(default_change_notice)
+
     steps_lines = []
     if not here:
         steps_lines.append(f"1. Go to the project folder: [cyan]cd {project_name}[/cyan]")

tests/integrations/test_cli.py

@@ -785,6 +785,32 @@ class TestGitExtensionAutoInstall:
         assert "will be removed" in normalized_output
         assert "git extension will no longer be enabled by default" in normalized_output
 
+    def test_default_git_auto_enable_emits_notice(self, tmp_path):
+        """Default git auto-enable emits notice about the v0.10.0 opt-in change."""
+        from typer.testing import CliRunner
+        from specify_cli import app
+
+        project = tmp_path / "git-default-notice"
+        project.mkdir()
+        old_cwd = os.getcwd()
+        try:
+            os.chdir(project)
+            runner = CliRunner()
+            result = runner.invoke(app, [
+                "init", "--here", "--ai", "claude", "--script", "sh",
+                "--ignore-agent-tools",
+            ], catch_exceptions=False)
+        finally:
+            os.chdir(old_cwd)
+
+        normalized_output = _normalize_cli_output(result.output)
+        assert result.exit_code == 0, result.output
+        # Check for key message components (notice may have box-drawing chars)
+        assert "git extension is currently enabled by default" in normalized_output
+        assert "v0.10.0" in normalized_output
+        assert "explicit opt-in" in normalized_output
+        assert "specify extension add git" in normalized_output
+
     def test_git_extension_commands_registered(self, tmp_path):
         """Git extension commands are registered with the agent during init."""
         from typer.testing import CliRunner