fix(dasha): judge antardasha sandhi from the unclipped start

Upstream 3c2dad95, rewritten for this tree. A birth-clipped antardasha start was reported as a transition. The first mahadasha start stays, because BUG-1268 already stores the real pre-birth boundary there. BUG-1382.

Co-Authored-By: Grok (agent loop)
Co-authored-by: Cursor <cursoragent@cursor.com>

docs/BUG_HISTORY.md

@@ -36518,3 +36518,18 @@
 - 相关记录：BUG-1268、BUG-1380。
 - 复发自：无。
 - 修复版本：分支 `codex/upstream-sync8-20261017`。上游提交 `3c2dad95`、`8643bc9a`、`9e04f0db`。
+
+## BUG-1382 | 出生日被当成小运交接
+
+- 状态：resolved
+- 首次发现 / 最近更新：2026-10-17 / 2026-10-18
+- 来源：issue #80，任务书 T3。上游 `3c2dad95` 的 Sandhi 部分，按我方数据改写。检索「dasha_sandhi」「unclipped_start」，没有更早的同类记录。
+- 现象：出生后 30 天内的盘，Sandhi 表把出生日写成一次小运交接。那一天只是第一段小运被裁到出生日，不是两段小运的交界。
+- 触发条件：`_calc_dasha_sandhi` 用裁剪后的 `start` 判断小运交接。默认参考时刻还带着当前的时分秒。
+- 根因：第一段小运的可见起点被改成了出生日。BUG-1268 之后，第一大运自己的 `start` 已经是出生前的真实交接，不能连大运起点一起跳过。
+- 修复：小运起点改用 `unclipped_start_datetime`。第一大运起点仍参与判断。没给参考日期时，参考时刻归零到当天 0 点。
+- 验证：`tests/test_dasha_sandhi_birth_clip.py`。虚构盘在出生后 30 天不再把出生日算成小运交接；出生前的大运起点仍在容限内出现。
+- 防复发：上述测试。
+- 相关记录：BUG-1268、BUG-1380。
+- 复发自：无。
+- 修复版本：分支 `codex/upstream-sync8-20261017`。上游提交 `3c2dad95`。

scripts/jyotish_engine.py

@@ -464,7 +464,7 @@ def _calc_sensitive_points(planets):
 
 
 def _calc_dasha_sandhi(dasha_result, reference_date=None, orb_days=90):
-    ref = datetime.strptime(reference_date, "%Y-%m-%d") if reference_date else datetime.now()
+    ref = datetime.strptime(reference_date, "%Y-%m-%d") if reference_date else datetime.now().replace(hour=0, minute=0, second=0, microsecond=0)
     sandhi = []
     timeline = dasha_result.get('timeline', []) if isinstance(dasha_result, dict) else []
     for md in timeline:
@@ -486,7 +486,11 @@ def _calc_dasha_sandhi(dasha_result, reference_date=None, orb_days=90):
             for boundary_key in ['start', 'end']:
                 if boundary_key not in ad:
                     continue
-                bdt = datetime.strptime(ad[boundary_key], "%Y-%m-%d")
+                # 被出生裁掉的小运起点不是交接。用完整起点判断，第一大运自己的 start 仍是出生前的真实交接，不跳过。
+                boundary_date = ad[boundary_key]
+                if boundary_key == 'start' and ad.get('unclipped_start_datetime'):
+                    boundary_date = datetime.fromisoformat(ad['unclipped_start_datetime']).strftime('%Y-%m-%d')
+                bdt = datetime.strptime(boundary_date, "%Y-%m-%d")
                 delta = (bdt - ref).days
                 if abs(delta) <= orb_days:
                     sandhi.append({
@@ -494,7 +498,7 @@ def _calc_dasha_sandhi(dasha_result, reference_date=None, orb_days=90):
                         'mahadasha_lord': md.get('lord'),
                         'lord': ad.get('lord'),
                         'boundary': boundary_key,
-                        'date': ad.get(boundary_key),
+                        'date': boundary_date,
                         'days_from_reference': delta,
                         'within_orb': True,
                     })

tests/test_dasha_sandhi_birth_clip.py

@@ -0,0 +1,60 @@
+"""A clipped birth balance is not an actual Dasha transition.
+
+Upstream ``tests/test_dasha_sandhi_birth_clip.py`` (3c2dad95) skips the first
+mahadasha start whenever ``is_balance`` is set. This tree does not: BUG-1268
+already stores the real pre-birth mahadasha boundary in ``start``.
+
+| 处 | 原值 | 新值 | 原因 |
+| --- | --- | --- | --- |
+| 第一大运 ``start`` | ``2000-01-01``，并跳过 ``is_balance`` 起点 | ``1998-01-01``，不跳过 | 我方第一大运起点是出生前的真实交接 |
+| 断言 | 跳过起点后窗口为空 | 起点超出容限，窗口仍为空 | 单独证明被裁剪的小运起点不算交接 |
+"""
+from types import SimpleNamespace
+
+from scripts.jyotish_engine import _calc_dasha_sandhi, cmd_dasha
+
+
+def test_birth_clip_does_not_create_a_transition():
+    data = {'timeline': [{'lord': 'Saturn', 'is_balance': True,
+        'start': '1998-01-01', 'end': '2010-01-01',
+        'antardasha_timeline': [{'lord': 'Mercury', 'start': '2000-01-01', 'end': '2002-01-01',
+            'unclipped_start_datetime': '1999-01-01T12:30:00'}]}]}
+    assert _calc_dasha_sandhi(data, '2000-01-01')['sandhi_windows'] == []
+
+
+def test_actual_unclipped_start_is_still_found():
+    data = {'timeline': [{'lord': 'Saturn', 'is_balance': True,
+        'start': '1998-01-01', 'end': '2010-01-01',
+        'antardasha_timeline': [{'lord': 'Mercury', 'start': '2000-01-01', 'end': '2002-01-01',
+            'unclipped_start_datetime': '1999-12-20T12:30:00'}]}]}
+    windows = _calc_dasha_sandhi(data, '2000-01-01', 30)['sandhi_windows']
+    assert len(windows) == 1
+    assert windows[0]['date'] == '1999-12-20'
+    assert windows[0]['days_from_reference'] == -12
+
+
+def test_real_boundaries_are_inclusive_at_orb_limit():
+    data = {'timeline': [{'lord': 'Sun', 'start': '2000-01-01', 'end': '2000-02-01'}]}
+    windows = _calc_dasha_sandhi(data, '2000-01-02', 1)['sandhi_windows']
+    assert len(windows) == 1 and windows[0]['date'] == '2000-01-01'
+
+
+def test_prebirth_mahadasha_start_is_not_discarded():
+    data = {'timeline': [{'lord': 'Saturn', 'is_balance': True,
+        'start': '1999-12-01', 'end': '2010-01-01',
+        'antardasha_timeline': []}]}
+    windows = _calc_dasha_sandhi(data, '2000-01-01', 90)['sandhi_windows']
+    assert [row['date'] for row in windows] == ['1999-12-01']
+
+
+def test_thirty_day_chart_does_not_list_the_birth_day_as_an_antardasha_join():
+    packet = cmd_dasha(SimpleNamespace(
+        moon_lon=20 / 3, nakshatra=None, pada=None,
+        birthdate='2000-01-01', year=2000, month=1, day=1, hour=12, minute=0, second=0,
+        lat=None, lon=None, tz=0, today='2000-01-31', dasha_year_days=365.25))
+    windows = _calc_dasha_sandhi(packet, '2000-01-31', 30)['sandhi_windows']
+    clipped = [
+        row for row in windows
+        if row['level'] == 'antardasha' and row['boundary'] == 'start' and row['date'] == '2000-01-01'
+    ]
+    assert clipped == []