feat(notify): persist notify_per_crack_enabled atomically

Add save_per_crack_enabled() as a data-layer sibling to save_enabled(),
using the same _atomic_rewrite primitive so mid-write crashes cannot
corrupt config.json.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hate_crack/notify/settings.py

@@ -147,6 +147,15 @@ def save_enabled(config_path: str, enabled: bool) -> None:
     _atomic_rewrite(config_path, _apply)
 
 
+def save_per_crack_enabled(config_path: str, enabled: bool) -> None:
+    """Persist ``notify_per_crack_enabled`` without disturbing other config keys."""
+
+    def _apply(data: dict) -> None:
+        data["notify_per_crack_enabled"] = bool(enabled)
+
+    _atomic_rewrite(config_path, _apply)
+
+
 def add_to_allowlist(config_path: str, attack_name: str) -> None:
     """Append ``attack_name`` to ``notify_attack_allowlist`` if absent.
 

tests/test_notify_settings.py

@@ -7,6 +7,7 @@ from hate_crack.notify.settings import (
     add_to_allowlist,
     load_settings,
     save_enabled,
+    save_per_crack_enabled,
 )
 
 
@@ -157,3 +158,32 @@ class TestAddToAllowlist:
         add_to_allowlist(str(config_path), "Brute Force")
         data = json.loads(config_path.read_text())
         assert data["notify_attack_allowlist"] == ["Brute Force"]
+
+
+class TestSavePerCrackEnabled:
+    def test_writes_new_config(self, tmp_path: Path) -> None:
+        config_path = tmp_path / "config.json"
+        save_per_crack_enabled(str(config_path), True)
+        data = json.loads(config_path.read_text())
+        assert data["notify_per_crack_enabled"] is True
+
+    def test_preserves_existing_keys(self, tmp_path: Path) -> None:
+        config_path = tmp_path / "config.json"
+        initial = {
+            "hcatBin": "hashcat",
+            "notify_enabled": True,
+            "notify_per_crack_enabled": False,
+        }
+        config_path.write_text(json.dumps(initial))
+        save_per_crack_enabled(str(config_path), True)
+        data = json.loads(config_path.read_text())
+        assert data["hcatBin"] == "hashcat"
+        assert data["notify_enabled"] is True
+        assert data["notify_per_crack_enabled"] is True
+
+    def test_toggles_back_and_forth(self, tmp_path: Path) -> None:
+        config_path = tmp_path / "config.json"
+        save_per_crack_enabled(str(config_path), True)
+        save_per_crack_enabled(str(config_path), False)
+        data = json.loads(config_path.read_text())
+        assert data["notify_per_crack_enabled"] is False