fix(backend): weekly score window is 7 days, not 8 (off-by-one) (#10015)

get_scores() documents its weekly window as "tasks created in the 7 days
ending on that date", but builds it as:

    day_end   = day + timedelta(days=1)
    week_start = day - timedelta(days=7)   # created_at in [day-7, day+1)

[day-7, day+1) spans 8 calendar days (day-7 .. day inclusive), so every task
created on the day-7 date is counted in the weekly totals, inflating
weekly.total_tasks and skewing weekly.score.

The adjacent daily window is built as [day, day+1) — exactly one day — which
fixes the intended construction: an N-day window ending on `day` is
[day-(N-1), day+1). For the 7-day weekly window that is [day-6, day+1).

Fix: week_start = day - timedelta(days=6). This preserves the created_at
field choice (the "matches Rust backend which uses created_at" comment is
about the field, not the window; the Rust backend has no weekly-score
window) and only corrects the span from 8 to 7 days.

Test: the existing get_scores coverage only asserted the query uses the
created_at field, never the window bounds. Added
test_weekly_window_spans_seven_days_ending_on_date, which captures the
FieldFilter calls and asserts the created_at lower bound for date=2026-07-19
is 2026-07-13 (day-6), not 2026-07-12 (day-7).

Verification: exercised the real get_scores with a mocked db + FieldFilter
tracker -> created_at >= 2026-07-13 (7-day span); reverting the one-line fix
yields 2026-07-12 (8-day span) and the new assertion fails.
black --line-length 120 --check: clean.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: arhxam

backend/database/action_items.py

@@ -1058,7 +1058,10 @@ def get_scores(uid: str, date: Optional[str] = None) -> Dict[str, Any]:
 
     day_start = day
     day_end = day + timedelta(days=1)
-    week_start = day - timedelta(days=7)
+    # "7 days ending on that date" is inclusive of `day`, so the window is
+    # [day-6, day+1) — mirroring the one-day daily window [day, day+1). Using
+    # day-7 spanned 8 calendar days and over-counted the weekly totals.
+    week_start = day - timedelta(days=6)
 
     col = db.collection('users').document(uid).collection(action_items_collection)
 

backend/tests/unit/test_desktop_migration.py

@@ -1634,6 +1634,41 @@ def col_where(**kwargs):
         # Verify created_at was used in filter calls (for weekly query)
         assert 'created_at' in captured_filters, f"Expected created_at in filters, got: {captured_filters}"
 
+    def test_weekly_window_spans_seven_days_ending_on_date(self):
+        """The weekly window is the 7 days ending on `date`, i.e. [date-6, date+1).
+
+        Regression: it was [date-7, date+1) — 8 calendar days — which over-counted
+        every task created on the date-7 day, inconsistent with the docstring and
+        with the one-day daily window [date, date+1).
+        """
+        from datetime import timedelta
+
+        mock_col = MagicMock()
+        empty = MagicMock()
+        empty.where.return_value = empty
+        empty.stream.return_value = []
+        mock_col.where.return_value = empty
+        mock_col.stream.return_value = []
+
+        captured = []  # (field, op, value)
+        original_ff = action_items_db.FieldFilter
+
+        def tracking_filter(field, op, value):
+            captured.append((field, op, value))
+            return original_ff(field, op, value)
+
+        with patch.object(action_items_db, 'db') as patched_db, patch.object(
+            action_items_db, 'FieldFilter', side_effect=tracking_filter
+        ):
+            patched_db.collection.return_value.document.return_value.collection.return_value = mock_col
+            action_items_db.get_scores('test-uid', date='2026-07-19')
+
+        day = datetime(2026, 7, 19, tzinfo=timezone.utc)
+        created_at_lower = [v for (f, op, v) in captured if f == 'created_at' and op == '>=']
+        assert created_at_lower, f"no created_at >= filter captured: {captured}"
+        # 7 days ending on 2026-07-19 -> lower bound is 2026-07-13 (day-6), not 2026-07-12 (day-7).
+        assert created_at_lower[0] == day - timedelta(days=6), created_at_lower[0]
+
     def test_default_tab_daily_when_highest(self):
         """default_tab is 'daily' when daily has tasks and highest score."""
         mock_col = MagicMock()