feat: 3.2.17中途变更处理(git驱动) + 3.2.9a Worker git强制 + 3.2.5 Phase7 squash merge + Arc git初始化检测

- 新增 ChangeClassifier（爆炸半径分类：IMPLEMENTATION/INTERFACE/GLOBAL_CONSTRAINT）
- 新增 ImpactPropagator（BFS影响传播：IMPACTED/BOUNDARY/SAFE差异化标记）
- task_graph.py：invalidate_by_adr()差异化失效 + CascadeReport扩展字段（向后兼容）
- eng_mode.py：三阶段差异化流程（分类→传播→失效→git操作→验证任务→重规划）
- eng_mode.py：_git_squash_merge_and_tag() + Phase 7 集成
- do_mode.py：_ensure_all_committed() Worker git操作强制
- adr_watcher.py：内容快照 + get_content_for_classification()
- events.py：ADR_CLASSIFIED/IMPACT_PROPAGATED/BOUNDARY_VERIFICATION_GENERATED
- partial_replanner.py：replan_with_constraints() + generate_verification_tasks()
- project_bootstrap.py：ensure_git_initialized() Arc规划前检测
- test_p1_21_phase2.py：21个新测试，95个全量测试0失败

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/air_runtime/project_bootstrap.py

@@ -5,9 +5,74 @@ V2 保持与 V1 相同的不变量：制品驱动通信、上下文隔离。
 
 from __future__ import annotations
 
+import subprocess
 from pathlib import Path
 
 
+def ensure_git_initialized(project_root: Path) -> dict:
+    """3.2.5: Arc 规划前 git 初始化检测。
+
+    检测项目是否为 git 仓库，至少有 1 个 commit。
+    如果没有则自动初始化并创建空提交，确保 worktree 操作可行。
+    """
+    git_dir = project_root / ".git"
+    result = {"git": False, "commits": False, "initialized": False}
+
+    if git_dir.exists():
+        result["git"] = True
+        try:
+            r = subprocess.run(
+                ["git", "rev-parse", "HEAD"],
+                cwd=project_root, capture_output=True, text=True, timeout=10,
+            )
+            if r.returncode == 0:
+                result["commits"] = True
+                return result
+        except Exception:
+            pass
+
+    # 初始化 git
+    if not result["git"]:
+        try:
+            subprocess.run(
+                ["git", "init"],
+                cwd=project_root, capture_output=True, timeout=10,
+            )
+            result["git"] = True
+        except Exception as e:
+            result["error"] = f"git init failed: {e}"
+            return result
+
+    # 创建初始提交
+    try:
+        subprocess.run(
+            ["git", "config", "user.email", "airplan@local"],
+            cwd=project_root, capture_output=True, timeout=5,
+        )
+        subprocess.run(
+            ["git", "config", "user.name", "AirPlan"],
+            cwd=project_root, capture_output=True, timeout=5,
+        )
+        # 创建 .gitkeep 确保有文件可提交
+        gitkeep = project_root / ".gitkeep"
+        if not gitkeep.exists():
+            gitkeep.touch()
+        subprocess.run(
+            ["git", "add", ".gitkeep"],
+            cwd=project_root, capture_output=True, timeout=10,
+        )
+        subprocess.run(
+            ["git", "commit", "-m", "AirPlan: initial empty commit"],
+            cwd=project_root, capture_output=True, timeout=10,
+        )
+        result["commits"] = True
+        result["initialized"] = True
+    except Exception as e:
+        result["error"] = f"initial commit failed: {e}"
+
+    return result
+
+
 def ensure_project_bootstrap(project_root: Path) -> dict[str, bool]:
     """创建 AirPlan 必需目录结构。"""
     root = project_root / "AirPlan"