fix: sliding period window for datetime precision

After --commit with precision=datetime, last_used held from==to==now,
so the next default period degenerated to a single second and showed
no new time entries. Now --commit stores the real report window start
and get_default_date_range() returns last_used.to..now for
datetime+dynamic mode.

Closes #70

tests/test_cli.py

@@ -715,7 +715,9 @@ class TestCommitFlag:
     def test_commit_with_precision_datetime_passes_datetime_strings(
         self, mock_save, mock_fetch, tmp_path
     ):
-        """При precision=datetime --commit сохраняет timestamps."""
+        """При precision=datetime --commit сохраняет from окна и to в naive UTC."""
+        from datetime import datetime
+
         import yaml
 
         issue = _MockIssue()
@@ -732,7 +734,7 @@ class TestCommitFlag:
             code = main(
                 [
                     "--date",
-                    "2026-06-30--2026-06-30",
+                    "2026-09-10T09:00:00--2026-09-12T18:00:00",
                     "--commit",
                     "--output",
                     str(tmp_path / "report.xlsx"),
@@ -745,17 +747,19 @@ class TestCommitFlag:
         call_args = mock_save.call_args
         assert call_args is not None
         saved_from, saved_to = call_args.args[1], call_args.args[2]
-        assert "T" in saved_from
-        assert "T" in saved_to
+        assert saved_from == "2026-09-10T09:00:00"
+        assert datetime.strptime(saved_to, "%Y-%m-%dT%H:%M:%S")
+        assert call_args.args[3] == "datetime"
+        assert call_args.args[4] is True
 
     @mock.patch.dict(os.environ, VALID_ENV, clear=True)
     @mock.patch("redmine_reporter.cli.fetch_issues_with_spent_time")
     @mock.patch("redmine_reporter.cli.save_period_to_config")
-    def test_commit_with_precision_datetime_saves_aware_utc(
+    def test_commit_with_precision_datetime_saves_naive_utc_to(
         self, mock_save, mock_fetch, tmp_path
     ):
-        """При precision=datetime --commit сохраняет last_used как aware UTC (#58)."""
-        from datetime import datetime, timezone
+        """При precision=datetime --commit сохраняет to как naive UTC (#70)."""
+        from datetime import datetime
 
         import yaml
 
@@ -773,7 +777,7 @@ class TestCommitFlag:
             code = main(
                 [
                     "--date",
-                    "2026-06-30--2026-06-30",
+                    "2026-09-10T09:00:00--2026-09-12T18:00:00",
                     "--commit",
                     "--output",
                     str(tmp_path / "report.xlsx"),
@@ -786,10 +790,60 @@ class TestCommitFlag:
         call_args = mock_save.call_args
         assert call_args is not None
         saved_from, saved_to = call_args.args[1], call_args.args[2]
-        for saved in (saved_from, saved_to):
-            parsed = datetime.fromisoformat(saved)
-            assert parsed.tzinfo is not None, f"{saved} must be timezone-aware"
-            assert parsed.utcoffset() == timezone.utc.utcoffset(None)
+        assert saved_from == "2026-09-10T09:00:00"
+        parsed = datetime.fromisoformat(saved_to)
+        assert parsed.tzinfo is None, f"{saved_to} must be naive UTC"
+
+    @mock.patch.dict(os.environ, VALID_ENV, clear=True)
+    @mock.patch("redmine_reporter.cli.fetch_issues_with_spent_time")
+    @mock.patch("redmine_reporter.cli.save_period_to_config")
+    def test_commit_datetime_persists_window_start_and_now(
+        self, mock_save, mock_fetch, tmp_path
+    ):
+        """--commit при datetime сохраняет начало окна и текущий naive UTC (#70)."""
+        from datetime import datetime as real_datetime
+
+        import yaml
+
+        issue = _MockIssue()
+        mock_fetch.return_value = [(issue, 1.0, None)]
+
+        config_path = tmp_path / "config.yml"
+        config_path.write_text(
+            yaml.dump({"period": {"precision": "datetime", "dynamic": True}})
+        )
+
+        fake_datetime = mock.MagicMock()
+        fake_datetime.fromisoformat = real_datetime.fromisoformat
+        fake_datetime.strptime = real_datetime.strptime
+        fake_datetime.now.return_value = real_datetime(2026, 9, 15, 12, 0, 0)
+
+        with mock.patch("redmine_reporter.cli.datetime", fake_datetime):
+            with mock.patch(
+                "redmine_reporter.cli.get_formatter_by_extension"
+            ) as mock_get:
+                mock_formatter = mock.MagicMock()
+                mock_get.return_value = mock_formatter
+                code = main(
+                    [
+                        "--commit",
+                        "--date",
+                        "2026-09-10T09:00:00--2026-09-12T18:00:00",
+                        "--output",
+                        str(tmp_path / "report.xlsx"),
+                        "--config-path",
+                        str(config_path),
+                    ]
+                )
+                assert code == 0
+
+        mock_save.assert_called_once_with(
+            str(config_path),
+            "2026-09-10T09:00:00",
+            "2026-09-15T12:00:00",
+            "datetime",
+            True,
+        )
 
     @mock.patch.dict(os.environ, VALID_ENV, clear=True)
     @mock.patch("redmine_reporter.cli.fetch_issues_with_spent_time")
@@ -1535,11 +1589,10 @@ class TestReportNoTimeIntegration:
 @mock.patch.dict(os.environ, VALID_ENV, clear=True)
 @mock.patch("redmine_reporter.cli.fetch_issues_with_spent_time")
 def test_cli_dynamic_datetime_period_without_date(mock_fetch, tmp_path):
-    """dynamic+datetime без --date: datetime-диапазон из last_used принимается.
+    """dynamic+datetime без --date: скользящее окно от last_used.to до now (#70).
 
-    Ожидаемое поведение после фикса #59: parse_date_range принимает диапазон
-    с временем (YYYY-MM-DDTHH:MM:SS), следующий период вычисляется от last_used,
-    отчёт строится без ошибки.
+    Ожидаемое поведение после фикса #70: дефолтный диапазон начинается с
+    last_used.to и заканчивается текущим моментом, а не сдвинутым периодом.
     """
     issue = _MockIssue()
     mock_fetch.return_value = [(issue, 1.0, None)]
@@ -1554,14 +1607,17 @@ def test_cli_dynamic_datetime_period_without_date(mock_fetch, tmp_path):
         "    to: '2026-06-30T23:59:59'\n"
     )
 
-    code = main(["--config-path", str(config_path)])
+    real_dt = __import__("datetime").datetime
+    with mock.patch("redmine_reporter.config.datetime") as dt:
+        dt.fromisoformat = real_dt.fromisoformat
+        dt.now.return_value = real_dt(2026, 7, 15, 10, 0, 0)
+        code = main(["--config-path", str(config_path)])
 
     assert code == 0
     args, _ = mock_fetch.call_args
     from_date, to_date = args[0], args[1]
-    # Следующий период после 2026-06-01T00:00:00--2026-06-30T23:59:59
-    assert from_date == "2026-07-01T00:00:00"
-    assert to_date == "2026-07-30T23:59:59"
+    assert from_date == "2026-06-30T23:59:59"
+    assert to_date == "2026-07-15T10:00:00"
 
 
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