fix: anchor Day N to each round's first game instead of lazy first sighting

The banner read "Day 1 of ~60" on day 2 of the playoffs because the old
anchor recorded whatever date we first polled a playoff game as Day 1.
Now round start dates come from /v1/schedule/playoff-series, so Day N
is authoritative and resets at each round boundary. Drops the noisy
"of ~60" denominator.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_playoff_cache.py

@@ -144,46 +144,112 @@ class TestFetchSeries:
         assert playoff_cache.fetch_series("2026-A") is None
 
 
-class TestRecordStartDate:
-    def test_no_playoff_games_no_write(self, tmp_db):
-        result = playoff_cache.record_start_date_if_missing([{"gameType": 2}])
-        assert result is None
-        assert playoff_cache.get_playoff_start_date() is None
+class TestRefreshRoundStartDates:
+    def test_no_bracket_returns_none(self, tmp_db):
+        assert playoff_cache.refresh_round_start_dates(2026) is None
 
-    def test_records_on_first_playoff_sighting(self, tmp_db):
-        now = datetime(2026, 4, 18, 20, 0, tzinfo=EASTERN)
-        result = playoff_cache.record_start_date_if_missing([{"gameType": 3}], now=now)
-        assert result == "2026-04-18"
-        assert playoff_cache.get_playoff_start_date().isoformat() == "2026-04-18"
-
-    def test_idempotent_after_first_write(self, tmp_db):
-        first_now = datetime(2026, 4, 18, 20, 0, tzinfo=EASTERN)
-        second_now = datetime(2026, 4, 25, 20, 0, tzinfo=EASTERN)
-        playoff_cache.record_start_date_if_missing([{"gameType": 3}], now=first_now)
-        # Second call should not overwrite
-        result = playoff_cache.record_start_date_if_missing(
-            [{"gameType": 3}], now=second_now
+    def test_anchors_round_to_earliest_game(self, tmp_db, monkeypatch):
+        playoff_cache._put(
+            playoff_cache.bracket_key(2026),
+            {"series": [{"seriesLetter": "A", "playoffRound": 1}]},
         )
-        assert result == "2026-04-18"
+        series_payload = {
+            "games": [
+                {"startTimeUTC": "2026-04-19T23:00:00Z"},
+                {"startTimeUTC": "2026-04-18T23:00:00Z"},
+                {"startTimeUTC": "2026-04-21T23:00:00Z"},
+            ]
+        }
+        monkeypatch.setattr(
+            "app.playoff_cache.requests.get",
+            lambda *a, **kw: _Resp(series_payload),
+        )
+
+        merged = playoff_cache.refresh_round_start_dates(2026)
+        assert merged == {"1": "2026-04-18"}
+        assert playoff_cache.get_round_start_date(1).isoformat() == "2026-04-18"
+
+    def test_merges_multiple_rounds_min_per_round(self, tmp_db, monkeypatch):
+        playoff_cache._put(
+            playoff_cache.bracket_key(2026),
+            {
+                "series": [
+                    {"seriesLetter": "A", "playoffRound": 1},
+                    {"seriesLetter": "B", "playoffRound": 1},
+                    {"seriesLetter": "I", "playoffRound": 2},
+                ]
+            },
+        )
+        payloads = {
+            "A": {"games": [{"startTimeUTC": "2026-04-19T23:00:00Z"}]},
+            "B": {"games": [{"startTimeUTC": "2026-04-18T23:00:00Z"}]},
+            "I": {"games": [{"startTimeUTC": "2026-04-29T23:00:00Z"}]},
+        }
+
+        def fake_get(url, *a, **kw):
+            letter = url.rstrip("/").rsplit("/", 1)[-1].upper()
+            return _Resp(payloads[letter])
+
+        monkeypatch.setattr("app.playoff_cache.requests.get", fake_get)
+
+        merged = playoff_cache.refresh_round_start_dates(2026)
+        assert merged == {"1": "2026-04-18", "2": "2026-04-29"}
+
+    def test_preserves_existing_rounds_on_merge(self, tmp_db, monkeypatch):
+        playoff_cache._put(
+            playoff_cache.ROUND_DATES_KEY, {"1": "2026-04-18", "2": "2026-04-29"}
+        )
+        playoff_cache._put(
+            playoff_cache.bracket_key(2026),
+            {"series": [{"seriesLetter": "M", "playoffRound": 3}]},
+        )
+        monkeypatch.setattr(
+            "app.playoff_cache.requests.get",
+            lambda *a, **kw: _Resp(
+                {"games": [{"startTimeUTC": "2026-05-15T23:00:00Z"}]}
+            ),
+        )
+
+        merged = playoff_cache.refresh_round_start_dates(2026)
+        assert merged["1"] == "2026-04-18"
+        assert merged["2"] == "2026-04-29"
+        assert merged["3"] == "2026-05-15"
 
 
-class TestDayN:
-    def test_no_start_date(self, tmp_db):
-        assert playoff_cache.day_n() == (None, None)
+class TestDayNForRound:
+    def test_no_round_num(self, tmp_db):
+        assert playoff_cache.day_n_for_round(None) is None
+
+    def test_round_not_anchored(self, tmp_db):
+        assert playoff_cache.day_n_for_round(1) is None
 
     def test_day_one(self, tmp_db):
+        playoff_cache._put(playoff_cache.ROUND_DATES_KEY, {"1": "2026-04-18"})
         now = datetime(2026, 4, 18, 20, 0, tzinfo=EASTERN)
-        playoff_cache.record_start_date_if_missing([{"gameType": 3}], now=now)
-        n, total = playoff_cache.day_n(now=now)
-        assert n == 1
-        assert total == 60
+        assert playoff_cache.day_n_for_round(1, now=now) == 1
+
+    def test_day_two(self, tmp_db):
+        playoff_cache._put(playoff_cache.ROUND_DATES_KEY, {"1": "2026-04-18"})
+        now = datetime(2026, 4, 19, 10, 0, tzinfo=EASTERN)
+        assert playoff_cache.day_n_for_round(1, now=now) == 2
 
     def test_day_five(self, tmp_db):
-        start = datetime(2026, 4, 18, 20, 0, tzinfo=EASTERN)
-        later = datetime(2026, 4, 22, 20, 0, tzinfo=EASTERN)
-        playoff_cache.record_start_date_if_missing([{"gameType": 3}], now=start)
-        n, _ = playoff_cache.day_n(now=later)
-        assert n == 5
+        playoff_cache._put(playoff_cache.ROUND_DATES_KEY, {"1": "2026-04-18"})
+        now = datetime(2026, 4, 22, 20, 0, tzinfo=EASTERN)
+        assert playoff_cache.day_n_for_round(1, now=now) == 5
+
+    def test_round_two_resets_to_day_one(self, tmp_db):
+        playoff_cache._put(
+            playoff_cache.ROUND_DATES_KEY,
+            {"1": "2026-04-18", "2": "2026-04-29"},
+        )
+        now = datetime(2026, 4, 29, 20, 0, tzinfo=EASTERN)
+        assert playoff_cache.day_n_for_round(2, now=now) == 1
+
+    def test_before_start_returns_none(self, tmp_db):
+        playoff_cache._put(playoff_cache.ROUND_DATES_KEY, {"2": "2026-04-29"})
+        now = datetime(2026, 4, 20, 20, 0, tzinfo=EASTERN)
+        assert playoff_cache.day_n_for_round(2, now=now) is None
 
 
 class TestSchema: