feat: carry overdue interval habits forward

tests/test_mvp_backend.py

@@ -443,12 +443,62 @@ def test_boolean_interval_habit_schedule(client):
     boot(client)
     habit = client.post(
         "/api/v1/habits",
-        json={"name": "拉伸", "kind": "boolean", "schedule_type": "interval", "interval_days": 2},
+        json={
+            "name": "拉伸",
+            "kind": "boolean",
+            "schedule_type": "interval",
+            "interval_days": 3,
+            "start_date": "2026-09-01",
+        },
     )
     assert habit.status_code == 201
-    assert client.post(
-        f"/api/v1/habits/{habit.json()['id']}/logs", json={"day": local_today().isoformat(), "value": 1}
-    ).json()["value"] == 1
+    habit_id = habit.json()["id"]
+
+    overdue_grid = client.get("/api/v1/habits/grid", params={"week": "2026-09-07"}).json()
+    overdue_cells = {cell["day"]: cell for cell in overdue_grid["habits"][0]["cells"]}
+    assert overdue_cells["2026-09-07"]["scheduled"] is True
+    assert overdue_cells["2026-09-08"]["scheduled"] is True
+    assert overdue_cells["2026-09-09"]["scheduled"] is True
+
+    completed = client.post(
+        f"/api/v1/habits/{habit_id}/logs", json={"day": "2026-09-09", "value": 1}
+    )
+    assert completed.status_code == 200
+
+    next_grid = client.get("/api/v1/habits/grid", params={"week": "2026-09-07"}).json()
+    next_cells = {cell["day"]: cell for cell in next_grid["habits"][0]["cells"]}
+    assert next_cells["2026-09-09"]["scheduled"] is True
+    assert next_cells["2026-09-10"]["scheduled"] is False
+    assert next_cells["2026-09-11"]["scheduled"] is False
+    assert next_cells["2026-09-12"]["scheduled"] is True
+    assert next_cells["2026-09-13"]["scheduled"] is True
+
+
+def test_interval_habit_partial_progress_does_not_restart_interval(client):
+    boot(client)
+    habit = client.post(
+        "/api/v1/habits",
+        json={
+            "name": "喝水",
+            "kind": "numeric",
+            "target": 3,
+            "schedule_type": "interval",
+            "interval_days": 3,
+            "start_date": "2026-09-01",
+        },
+    ).json()
+
+    assert client.put(f"/api/v1/habits/{habit['id']}/logs/2026-09-04", json={"value": 2}).status_code == 200
+    grid = client.get("/api/v1/habits/grid", params={"week": "2026-09-07"}).json()
+    cells = {cell["day"]: cell for cell in grid["habits"][0]["cells"]}
+    assert cells["2026-09-07"]["scheduled"] is True
+
+    assert client.put(f"/api/v1/habits/{habit['id']}/logs/2026-09-08", json={"value": 3}).status_code == 200
+    grid = client.get("/api/v1/habits/grid", params={"week": "2026-09-07"}).json()
+    cells = {cell["day"]: cell for cell in grid["habits"][0]["cells"]}
+    assert cells["2026-09-09"]["scheduled"] is False
+    assert cells["2026-09-10"]["scheduled"] is False
+    assert cells["2026-09-11"]["scheduled"] is True
 
 
 def test_attachment_security_ownership_and_size(client, tmp_path, monkeypatch):