fix(datetime): use date-specific offsets for naive call filters

src/vapi/core/datetime_utils.py

@@ -65,6 +65,5 @@ def _serialize_zoned_datetime(v: dt.datetime) -> str:
     if v.tzinfo is not None:
         return _serialize_zoned_datetime(v)
     else:
-        local_tz = dt.datetime.now().astimezone().tzinfo
-        localized_dt = v.replace(tzinfo=local_tz)
+        localized_dt = v.astimezone()
         return _serialize_zoned_datetime(localized_dt)

tests/custom/test_call_filter_timezone.py

@@ -0,0 +1,72 @@
+import datetime as dt
+import os
+import time
+
+import httpx
+import pytest
+
+from vapi import AsyncVapi, Vapi
+
+
+@pytest.fixture
+def pacific_timezone():
+    if not hasattr(time, "tzset"):
+        pytest.skip("runtime timezone switching requires time.tzset")
+    previous = os.environ.get("TZ")
+    os.environ["TZ"] = "America/Los_Angeles"
+    time.tzset()
+    try:
+        yield
+    finally:
+        if previous is None:
+            os.environ.pop("TZ", None)
+        else:
+            os.environ["TZ"] = previous
+        time.tzset()
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.parametrize(
+    "field,wire_field",
+    [
+        ("created_at_ge", "createdAtGe"),
+        ("created_at_le", "createdAtLe"),
+        ("updated_at_ge", "updatedAtGe"),
+        ("updated_at_le", "updatedAtLe"),
+    ],
+)
+@pytest.mark.parametrize(
+    "value,expected",
+    [
+        (dt.datetime(2026, 1, 15, 12), "2026-01-15T12:00:00-08:00"),
+        (dt.datetime(2026, 7, 15, 12), "2026-07-15T12:00:00-07:00"),
+        (dt.datetime(2026, 11, 1, 1, 30, fold=0), "2026-11-01T01:30:00-07:00"),
+        (dt.datetime(2026, 11, 1, 1, 30, fold=1), "2026-11-01T01:30:00-08:00"),
+        (dt.datetime(2026, 1, 15, 12, tzinfo=dt.timezone.utc), "2026-01-15T12:00:00Z"),
+        (
+            dt.datetime(2026, 1, 15, 12, tzinfo=dt.timezone(dt.timedelta(hours=5, minutes=30))),
+            "2026-01-15T12:00:00+05:30",
+        ),
+        (dt.datetime(2026, 1, 15, 12, 0, 0, 123456), "2026-01-15T12:00:00.123456-08:00"),
+    ],
+)
+async def test_call_filters_use_date_specific_local_offset(
+    pacific_timezone, asynchronous, field, wire_field, value, expected
+):
+    requests = []
+
+    def respond(request):
+        requests.append(request)
+        return httpx.Response(200, json=[])
+
+    if asynchronous:
+        async with httpx.AsyncClient(transport=httpx.MockTransport(respond)) as http:
+            client = AsyncVapi(token="test", httpx_client=http)
+            result = await client.calls.list(**{field: value})
+    else:
+        with httpx.Client(transport=httpx.MockTransport(respond)) as http:
+            client = Vapi(token="test", httpx_client=http)
+            result = client.calls.list(**{field: value})
+    assert result == []
+    assert len(requests) == 1
+    assert requests[0].url.params[wire_field] == expected