disallow to disable guard during focus

backend/app/services/settings_service.py

@@ -20,7 +20,7 @@ from sqlalchemy.orm import Session
 
 from app.config import env_settings
 from app.models import SettingsRow
-from app.services import pomodoro
+from app.services import blocker_service, pomodoro
 from app.settings_schema import SECRET_FIELDS, SECRET_MASK, AppSettings
 
 _SETTINGS_ID = 1
@@ -192,10 +192,17 @@ def unmask_secrets(stored: dict[str, Any], incoming: dict[str, Any]) -> dict[str
 
 def apply_patch(session: Session, patch: dict[str, Any]) -> AppSettings:
     """Merge a partial settings document (as the UI sends it) and store it."""
-    current = load_settings(session).model_dump(mode="json")
+    stored = load_settings(session)
+    current = stored.model_dump(mode="json")
     patch = unmask_secrets(current, patch)
     merged = _merge(current, patch)
-    updated = save_settings(session, AppSettings.model_validate(merged))
+    candidate = AppSettings.model_validate(merged)
+
+    # Validate, then refuse, then write: a malformed patch stays a 422 rather
+    # than becoming a 409, and nothing is stored either way.
+    blocker_service.ensure_guard_not_switched_off(session, stored, candidate)
+
+    updated = save_settings(session, candidate)
 
     # A changed Focus/Short/Long minute (directly, or via a preset) resizes
     # whatever interval is already running or paused — see
@@ -203,3 +210,16 @@ def apply_patch(session: Session, patch: dict[str, Any]) -> AppSettings:
     # is simplest to always run it rather than detect which keys changed.
     pomodoro.rescale_current(session, updated)
     return updated
+
+
+def reset_to_env(session: Session) -> AppSettings:
+    """Back to the environment seed — refused if that would unguard a live interval.
+
+    `settings_from_env` never touches the `blocker` subtree, so a reset always
+    lands on the schema default `enabled = False`: without this check one POST
+    would switch the focus guard off mid-interval.
+    """
+    stored = load_settings(session)
+    fresh = settings_from_env()
+    blocker_service.ensure_guard_not_switched_off(session, stored, fresh)
+    return save_settings(session, fresh)