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/change_classifier.py

@@ -0,0 +1,101 @@
+"""
+ADR 变更爆炸半径分类 — P1-21 / 3.2.17 Phase 1 组件。
+将 ADR 内容变更按影响范围分为 IMPLEMENTATION / INTERFACE / GLOBAL_CONSTRAINT 三级。
+"""
+
+from __future__ import annotations
+
+import enum
+from dataclasses import dataclass, field
+from pathlib import Path
+
+
+class BlastRadius(enum.Enum):
+    IMPLEMENTATION = "implementation"
+    INTERFACE = "interface"
+    GLOBAL_CONSTRAINT = "global_constraint"
+
+
+@dataclass
+class ChangeClassification:
+    adr_id: str
+    blast_radius: BlastRadius
+    reason: str = ""
+    changed_sections: list[str] = field(default_factory=list)
+
+
+class ChangeClassifier:
+    """基于关键词启发式的 ADR 变更爆炸半径分类。
+
+    分类规则：
+    - IMPLEMENTATION: 仅实现细节变更，不影响公开接口。关键词：implementation detail, can use, for example, internal, private
+    - INTERFACE: 公开 API/合约变更。关键词：interface, api, contract, signature, must implement, public header, exported, caller
+    - GLOBAL_CONSTRAINT: 跨模块约束变更。关键词：must, shall, all modules, coding standard, every module, entire system, global policy
+
+    回退策略：内容不足无法确定时回退到 INTERFACE（保守：宁可多失效不少失效）。
+    """
+
+    _INTERFACE_KEYWORDS = [
+        "interface", "api", "contract", "signature", "must implement",
+        "public header", "exported", "caller",
+    ]
+    _GLOBAL_KEYWORDS = [
+        "must", "shall", "all modules", "coding standard",
+        "every module", "entire system", "global policy",
+    ]
+    _IMPLEMENTATION_KEYWORDS = [
+        "implementation detail", "can use", "for example",
+        "internally", "private", "optional",
+    ]
+
+    def classify(self, adr_id: str, old_content: str | None,
+                 new_content: str | None) -> ChangeClassification:
+        if new_content is None:
+            return ChangeClassification(
+                adr_id=adr_id, blast_radius=BlastRadius.GLOBAL_CONSTRAINT,
+                reason="ADR deleted — all dependent tasks must be invalidated",
+            )
+        if old_content is None:
+            return ChangeClassification(
+                adr_id=adr_id, blast_radius=BlastRadius.IMPLEMENTATION,
+                reason="new ADR — no existing tasks to invalidate",
+            )
+
+        text = new_content.lower()
+
+        global_hits = sum(1 for kw in self._GLOBAL_KEYWORDS if kw in text)
+        interface_hits = sum(1 for kw in self._INTERFACE_KEYWORDS if kw in text)
+        impl_hits = sum(1 for kw in self._IMPLEMENTATION_KEYWORDS if kw in text)
+
+        if global_hits >= 2:
+            return ChangeClassification(
+                adr_id=adr_id, blast_radius=BlastRadius.GLOBAL_CONSTRAINT,
+                reason=f"global constraint keywords matched ({global_hits} hits)",
+            )
+        if interface_hits >= 2:
+            return ChangeClassification(
+                adr_id=adr_id, blast_radius=BlastRadius.INTERFACE,
+                reason=f"interface keywords matched ({interface_hits} hits)",
+            )
+        if interface_hits >= 1:
+            return ChangeClassification(
+                adr_id=adr_id, blast_radius=BlastRadius.INTERFACE,
+                reason="interface keyword matched — conservative classification",
+            )
+        if impl_hits >= interface_hits and impl_hits > 0:
+            return ChangeClassification(
+                adr_id=adr_id, blast_radius=BlastRadius.IMPLEMENTATION,
+                reason=f"implementation keywords matched ({impl_hits} hits)",
+            )
+
+        # 无法确定 → 保守回退
+        return ChangeClassification(
+            adr_id=adr_id, blast_radius=BlastRadius.INTERFACE,
+            reason="inconclusive — defaulting to INTERFACE (conservative)",
+        )
+
+    def classify_from_files(self, adr_id: str, old_path: Path | None,
+                            new_path: Path | None) -> ChangeClassification:
+        old_content = old_path.read_text(encoding="utf-8") if old_path and old_path.exists() else None
+        new_content = new_path.read_text(encoding="utf-8") if new_path and new_path.exists() else None
+        return self.classify(adr_id, old_content, new_content)