diff --git a/scripts/jyotish_engine.py b/scripts/jyotish_engine.py
index 6b94f848..f745c2f2 100644
--- a/scripts/jyotish_engine.py
+++ b/scripts/jyotish_engine.py
@@ -735,12 +735,24 @@ def _birth_datetime_from_args(args):
 
 
 def _compute_chart_from_args(args):
-    return compute_chart_data(
-        args.year, args.month, args.day, args.hour, args.minute,
-        args.lat, args.lon, args.tz, getattr(args, 'node_mode', 'mean'),
-        second=_arg_second(args),
-        ayanamsa_name=_current_ayanamsa_name(args),
-    )
+    from domain_calculation_service import compute_chart
+
+    result = compute_chart({
+        'year': args.year,
+        'month': args.month,
+        'day': args.day,
+        'hour': args.hour,
+        'minute': args.minute,
+        'second': _arg_second(args),
+        'lat': args.lat,
+        'lon': args.lon,
+        'tz': args.tz,
+        'node_mode': getattr(args, 'node_mode', 'mean'),
+        'ayanamsa': _current_ayanamsa_name(args),
+    })
+    asc_idx = SIGNS.index(result['ascendant']['sign'])
+    birth = result['birth_info']
+    return result, asc_idx, birth['julian_day'], birth['ayanamsa']
 
 
 def _current_ayanamsa_name(args=None):
diff --git a/tests/test_calculation_p0_regressions.py b/tests/test_calculation_p0_regressions.py
new file mode 100644
index 00000000..05338e08
--- /dev/null
+++ b/tests/test_calculation_p0_regressions.py
@@ -0,0 +1,117 @@
+from __future__ import annotations
+
+import sys
+from datetime import datetime
+from pathlib import Path
+from types import SimpleNamespace
+
+import pytest
+
+SCRIPTS = Path(__file__).resolve().parents[1] / "scripts"
+if str(SCRIPTS) not in sys.path:
+    sys.path.insert(0, str(SCRIPTS))
+
+import domain_calculation_service as calculation_service  # noqa: E402
+import jyotish_api_server  # noqa: E402
+from jyotish_api_server import JyotishAPIHandler  # noqa: E402
+from jyotish_engine import _compute_chart_from_args  # noqa: E402
+
+BIRTH = {
+    "year": 1990,
+    "month": 1,
+    "day": 1,
+    "hour": 12,
+    "minute": 0,
+    "second": 0,
+    "lat": 28.6139,
+    "lon": 77.2090,
+    "tz": 5.5,
+    "ayanamsa": "lahiri",
+}
+
+
+def test_true_node_changes_effective_rahu_and_contract() -> None:
+    mean = calculation_service.compute_chart({**BIRTH, "node_mode": "mean"})
+    true = calculation_service.compute_chart({**BIRTH, "node_mode": "true"})
+
+    assert mean["planets"]["Rahu"]["lon"] != pytest.approx(
+        true["planets"]["Rahu"]["lon"], abs=1e-8
+    )
+    assert mean["calculation_contract"]["effective"]["node_mode"] == "mean"
+    assert true["calculation_contract"]["effective"]["node_mode"] == "true"
+    assert mean["result_hash"] != true["result_hash"]
+
+
+def test_vimshottari_uses_birth_balance_as_canonical_timeline() -> None:
+    birth_dt = datetime(1990, 1, 1, 12, 0)
+    result = calculation_service.compute_vimshottari_timeline(
+        birth_dt=birth_dt,
+        moon_lon=100.0,
+        current_date=birth_dt,
+    )
+
+    first = result["periods"][0]
+    assert first["lord"] == "Saturn"
+    assert first["start"] == "1980-07-02"
+    assert first["end"] == "1999-07-02"
+    assert result["birth_balance"]["remaining_years"] == pytest.approx(9.5)
+    assert result["calculation_contract"]["algorithm"] == "vimshottari_birth_balance"
+
+
+def test_sade_sati_uses_real_saturn_transit_for_reference_date() -> None:
+    result = calculation_service.compute_sade_sati(
+        moon_degree=300.0,
+        asc_degree=330.0,
+        reference_date="2026-07-11",
+        tz=5.5,
+        ayanamsa="lahiri",
+    )
+    oracle = calculation_service.compute_transit_longitude(
+        planet="Saturn",
+        reference_date="2026-07-11",
+        tz=5.5,
+        ayanamsa="lahiri",
+    )
+
+    assert result["transit_saturn_lon"] == pytest.approx(oracle["longitude"], abs=1e-8)
+    assert result["provenance"]["data_layer"] == "true_transit_positions"
+    assert result["provenance"]["reference_date"] == "2026-07-11"
+
+
+def test_timezone_inference_fails_closed(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(
+        calculation_service,
+        "_lookup_timezone_name",
+        lambda _lat, _lon: None,
+    )
+
+    with pytest.raises(calculation_service.TimezoneInferenceError, match="timezone inference"):
+        calculation_service.infer_timezone_offset(
+            lat=0.0,
+            lon=0.0,
+            local_datetime=datetime(1990, 1, 1, 12, 0),
+        )
+
+
+def test_chart_hash_matches_domain_cli_and_rest(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("JYOTISH_API_CHART_CACHE_TTL_SECONDS", "0")
+    monkeypatch.setenv("VEDASTRO_ENABLE_NETWORK", "0")
+    monkeypatch.setattr(
+        jyotish_api_server,
+        "_attach_vedastro_main_entry_overview",
+        lambda result, _birth: result,
+    )
+    expected = calculation_service.compute_chart({**BIRTH, "node_mode": "true"})
+    cli, _asc_idx, _jd, _ayanamsa = _compute_chart_from_args(
+        SimpleNamespace(**BIRTH, node_mode="true")
+    )
+    rest = JyotishAPIHandler.__new__(JyotishAPIHandler)._compute_chart_sync(
+        {**BIRTH, "node_mode": "true", "transit_date": "2026-07-11"}
+    )
+
+    assert cli["result_hash"] == expected["result_hash"]
+    assert rest["result_hash"] == expected["result_hash"]
+    assert rest["birth"]["node_mode"] == "true"
+    assert rest["calculation_contract"]["effective"]["node_mode"] == "true"