Hyundai: cover ALT_LIMITS_2 in test_alternate_limits

[johnnathanwood]

Summary

test_alternate_limits verifies that the car-side ALT_LIMITS (270 Nm) flag is propagated to the
panda safetyParam, but the sibling ALT_LIMITS_2 (170 Nm) tier — added for the Kona 2022 in #2072 —
has no equivalent assertion. This adds the missing symmetric check.

Why it matters

The panda steer-torque tier is selected fail-open: with no flag set, opendbc/safety/modes/hyundai.h
falls back to the 384 Nm default. The car cap (CarControllerParams.STEER_MAX) and the panda tier are
derived independently, and panda cannot re-derive the per-car limit from the bus. So if the
ALT_LIMITS_2 flag is set on the car but not propagated into safetyParam (interface.py), panda
silently enforces 384 for a car that intends 170 — with no RX/TX/controls_allowed symptom. That is
the "a simple bug can silently allow more torque than expected" failure mode noted in #1137, and the
dropped-flag regression seen in #2072. The 270 tier is guarded against this today; the 170 tier was not.

Change

Test-only. One added assertion in test_alternate_limits, mirroring the existing ALT_LIMITS line for
ALT_LIMITS_2.

Test plan

• pytest opendbc/car/hyundai/tests/test_hyundai.py -k test_alternate_limits — passes on master.
• Verified it fails when the ALT_LIMITS_2 → safetyParam mapping in interface.py is removed: the Kona
  then reports a safetyParam missing the bit, so the assertion catches the silent fall-back to 384.

Scope / non-goals

• No behavior change; no generated code touched — the car_diff replay should report 0 changed.
• Guards the flag→safetyParam propagation only. It intentionally does not assert a per-platform
  expected cap: STEER_MAX is also set to non-default values by the CAN-FD and 255 Nm branches ahead of
  the ALT_LIMITS branches, so a blanket per-CAR "car cap == panda tier" assertion would false-fail on
  those cars.

[github-actions]

Car behavior report

Replays driving segments through this PR and compares the behavior to master.
Please review any changes carefully to ensure they are expected.

Testing 260 segments for: HYUNDAI_AZERA_HEV_6TH_GEN, HYUNDAI_ELANTRA_GT_I30, HYUNDAI_ELANTRA_2021, HYUNDAI_ELANTRA_HEV_2021, HYUNDAI_GENESIS, HYUNDAI_IONIQ, HYUNDAI_IONIQ_HEV_2022, HYUNDAI_IONIQ_EV_2020, HYUNDAI_IONIQ_PHEV_2019, HYUNDAI_IONIQ_PHEV, HYUNDAI_KONA_2022, HYUNDAI_KONA_EV, HYUNDAI_KONA_EV_2022, HYUNDAI_KONA_EV_2ND_GEN, HYUNDAI_SANTA_FE, HYUNDAI_SANTA_FE_2022, HYUNDAI_SANTA_FE_HEV_2022, HYUNDAI_SANTA_FE_PHEV_2022, HYUNDAI_SONATA, HYUNDAI_SONATA_LF, HYUNDAI_STARIA_4TH_GEN, HYUNDAI_PALISADE, HYUNDAI_SONATA_HYBRID, HYUNDAI_IONIQ_5, HYUNDAI_IONIQ_6, HYUNDAI_TUCSON_4TH_GEN, HYUNDAI_SANTA_CRUZ_1ST_GEN, HYUNDAI_CUSTIN_1ST_GEN

✅ 0 changed, 256 passed, 4 errors

Show errors

Traceback (most recent call last):
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 86, in process_segment
    can_msgs = load_can_messages(seg)
               ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 57, in load_can_messages
    msgs = LogReader(url, only_union_types=True, sort_by_time=True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/logreader.py", line 31, in __init__
    dat = f.read()
          ^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 500, in read
    s = self._safe_read(self.length)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 650, in _safe_read
    raise IncompleteRead(data, amt - len(data))
http.client.IncompleteRead: IncompleteRead(0 bytes read, 2581970 more expected)


Traceback (most recent call last):
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 86, in process_segment
    can_msgs = load_can_messages(seg)
               ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 57, in load_can_messages
    msgs = LogReader(url, only_union_types=True, sort_by_time=True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/logreader.py", line 31, in __init__
    dat = f.read()
          ^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 500, in read
    s = self._safe_read(self.length)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 650, in _safe_read
    raise IncompleteRead(data, amt - len(data))
http.client.IncompleteRead: IncompleteRead(0 bytes read, 3601038 more expected)


Traceback (most recent call last):
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 86, in process_segment
    can_msgs = load_can_messages(seg)
               ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 57, in load_can_messages
    msgs = LogReader(url, only_union_types=True, sort_by_time=True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/logreader.py", line 31, in __init__
    dat = f.read()
          ^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 500, in read
    s = self._safe_read(self.length)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 650, in _safe_read
    raise IncompleteRead(data, amt - len(data))
http.client.IncompleteRead: IncompleteRead(0 bytes read, 1882216 more expected)


Traceback (most recent call last):
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 86, in process_segment
    can_msgs = load_can_messages(seg)
               ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/tests/car_diff.py", line 57, in load_can_messages
    msgs = LogReader(url, only_union_types=True, sort_by_time=True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/opendbc/opendbc/opendbc/car/logreader.py", line 31, in __init__
    dat = f.read()
          ^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 500, in read
    s = self._safe_read(self.length)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/http/client.py", line 650, in _safe_read
    raise IncompleteRead(data, amt - len(data))
http.client.IncompleteRead: IncompleteRead(0 bytes read, 1865472 more expected)