VW: allow adjusting set speed when disabled

[RJWadley]

goal: more closely align with stock ACC behavior on VW cars with independent speed buttons

some cars have +/- buttons that are separate. realistically for openpilot this just means VW, since most other affected cars use flexray, but it's not inherently a VW thing. KIA EV9 has independent buttons for example, but it still treats them as SET+ and SET- so they're not affected here.

Since it has independent buttons, VW's stock system allows adjustment of the set point while disabled. In most cars, the +/- buttons are shared with RES/SET and this is inherently not possible.

tweaks:

• handle cruise +/- presses when disabled
• skip if we don't have an ACC setpoint
• tweak speed adjustment handling to ignore any button press that could enable openpilot

VW MQB	KIA EV6

Sample route showing adjustment while disabled:
a3d353f2254caee4/00000242--cb0f881531/0

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[andiradulescu]

One side effect on non-VW non-PCM brands worth considering:

Their base update_button_enable fires on +/- release, so those buttons double as enable triggers. With the if not enabled: return gone, the long-press branch at cruise.py:84-88 now ticks v_cruise_kph every 50 frames during a hold, even while disabled (as long as v_cruise_initialized). On + specifically, the drift survives the enable transition because initialize_v_cruise restores v_cruise_kph_last for accelCruise/resumeCruise. Net: hold + for 2s to re-engage → openpilot enables with setpoint +20 kph. Held - is fine, it gets clobbered by the else branch.

GM is worse, it enables on the rising edge of accelCruise (gm/carstate.py:34-41), so the drift happens live during the hold rather than all at once on release. The new CS.buttonEnable guard doesn't fire mid-hold, so it doesn't protect GM; the old button_change_states[...]["enabled"] guard did.

Since the feature is really "this car has independent set-speed buttons," I'd scope it to VW explicitly and keep the old guard intact for everyone else:

if not enabled and self.CP.brand != 'volkswagen':
  return

# ...

if not self.button_change_states[button_type]["enabled"] and self.CP.brand != 'volkswagen':
  return

Brand checks are already standard in this area (car_specific.py, latcontrol_angle.py, etc.), though cruise.py has none today. If you'd rather keep it brand-agnostic, a CarParams flag (hasIndependentSetSpeedButtons or similar) set by the VW interface would work too, at the cost of an opendbc capnp bump. The new CS.buttonEnable and not enabled_before_pressing guard can then be dropped - the restored old guard is strictly stronger.

On testing: this PR needs tests. I took a stab at coverage for the adjust-while-disabled paths on https://github.com/andiradulescu/openpilot/commits/set-speed/ - feel free to cherry-pick, fold in, or ignore. That branch also carries a latent precedence bug fix in test_rising_edge_enable, which I separately opened as #37802.

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Process replay diff report

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

✅ 0 changed, 66 passed, 0 errors

[RJWadley]

thanks for the feedback @andiradulescu!

I hadn't considered how openpilot would behave while disabled during a button hold. I cooked up some tests to cover some of the missing cases and this branch does indeed fail in exactly the scenarios you've described! master as-is passes.

In the short term, a branch check is probably the simplest fix. I'd rather keep it generic but it's not possible with openpilot's button handling at the moment.