fix: restore ayanamsa state and keep tests hermetic

scripts/ayanamsa_utils.py

@@ -10,7 +10,8 @@ comparison fixtures must pass an explicit `lahiri` name.
 
 from __future__ import annotations
 
-from typing import Any
+from contextlib import contextmanager
+from typing import Any, Iterator
 
 try:
     import swisseph as swe
@@ -91,6 +92,7 @@ def current_ayanamsa_name(args: Any = None) -> str:
 
 def apply_ayanamsa(name: Any = None, swe_module: Any = None) -> bool:
     """Set Swiss Ephemeris sidereal mode explicitly."""
+    global ACTIVE_AYANAMSA_NAME
     module = swe_module or swe
     if module is None:
         return False
@@ -99,9 +101,24 @@ def apply_ayanamsa(name: Any = None, swe_module: Any = None) -> bool:
         module.set_sid_mode(AYANAMSA_MODES[key])
     except Exception:
         return False
+    ACTIVE_AYANAMSA_NAME = key
     return True
 
 
+@contextmanager
+def temporary_ayanamsa(name: Any = None, swe_module: Any = None) -> Iterator[str]:
+    """Apply a sidereal mode and restore the previous process-wide mode."""
+    previous = ACTIVE_AYANAMSA_NAME
+    target = normalize_ayanamsa_name(name)
+    if not apply_ayanamsa(target, swe_module):
+        raise RuntimeError(f"failed to apply ayanamsa {target}")
+    try:
+        yield target
+    finally:
+        if not apply_ayanamsa(previous, swe_module):
+            raise RuntimeError(f"failed to restore ayanamsa {previous}")
+
+
 def sidereal_flags(swe_module: Any, ayanamsa_name: Any = None) -> int:
     apply_ayanamsa(ayanamsa_name, swe_module)
     return getattr(swe_module, 'FLG_SWIEPH', 2) | getattr(swe_module, 'FLG_SIDEREAL', 65536)