Created spec for issue #2165

.specify/features/git-extension-deprecation-notice/spec.md

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+# Add notice that git extension will no longer be enabled by default at 1.0.0
+
+> **Source**: [#2165](https://github.com/github/spec-kit/issues/2165) — imported on 2026-04-12
+
+## Overview
+
+Add a deprecation notice during `specify init` to inform users that the git extension, currently auto-enabled by default, will require explicit opt-in starting with v1.0.0. This ensures users are aware of the upcoming behavioral change well in advance.
+
+## Problem Statement
+
+The `git` extension is currently bundled and enabled by default during `specify init`. Starting with v1.0.0, it will still be bundled but no longer enabled by default — users will need to explicitly opt in. Without advance notice, users may be surprised by this change when upgrading to v1.0.0.
+
+## Requirements
+
+### Functional Requirements
+
+- FR-1: During `specify init`, display a warning notice when the git extension is auto-enabled
+- FR-2: The notice must clearly state the timeline (v1.0.0) for the change
+- FR-3: The notice must explain how to opt in after the change (`specify init --extension git` or `specify extension add git`)
+- FR-4: The notice must be non-blocking (warning styling, does not halt initialization)
+
+### Non-Functional Requirements
+
+- NFR-1: Notice should use yellow/warning styling consistent with existing CLI warning patterns
+- NFR-2: Notice should be concise and actionable
+
+## User Scenarios
+
+### Scenario 1: User runs specify init and sees deprecation notice
+
+**Given** a user is initializing a new project with `specify init`
+**When** the git extension is auto-enabled as part of the default behavior
+**Then** a warning notice is displayed informing them that the git extension will require explicit opt-in starting with v1.0.0
+
+### Scenario 2: User understands how to opt in after v1.0.0
+
+**Given** a user sees the deprecation notice during `specify init`
+**When** they read the notice
+**Then** they understand they can use `specify init --extension git` or `specify extension add git` to enable the git extension after v1.0.0
+
+## Acceptance Criteria
+
+- [ ] AC-1: `specify init` shows a notice when the git extension is auto-enabled
+- [ ] AC-2: Notice is visible but non-blocking (yellow/warning styling)
+- [ ] AC-3: Message clearly states the timeline (v1.0.0) and how to opt in
+
+## Out of Scope
+
+- Changes to the git extension itself or its functionality
+- Changes to the bundled status of the git extension (it remains bundled/shipped with spec-kit)
+- Actually removing the default-enabled behavior (that happens at v1.0.0, not now)