Double handle controls issue

Power handle doesn't move when brake handle isn't in B0.

On another hand thought it could be a feature, but in most cases irl it's only power handle and it's interlocked with reverser

Fixed.

Minor oversight when moving some code to the handle properties.

You're right though, should be a feature, so added it
New handle type available of Separated (Interlocked) which prevents the power handle being moved from N if the brake is applied. (If power is in use, the setting will be maintained, but returns to N if the handle position is modified)

Not sure if there are any separate handle trains with this kind of interlock, usually it's reverser and power/combined handle with 3 possible scenarios:
- 2 handles, power handle can only be moved with reverser in F or R, reverser can't be moved if handle isn't in 0
- combined handle, can only be moved with reverser in F or R, reverser can't be moved if handle isn't in coast
- combined handle, can only be moved with reverser in F or R, reverser can't be moved if handle isn't in emergency or handle off (if it's provided) position

Speaking of handle off, there are 2 common options too, before emergency notch and behind it.

I try not to get into more detail like auto brake positions behind EPB, interlocking with a control switch/key and more "non-Japanese" combos like combined handle on one side and air brake valve on another, or split levers for air and dynamic brake that can be linked and unlinked

I suspect stuff like this really depends on the exact form of interlocking (and hence the method chosen to simulate it), and gets very manufacturer / age specific in a hurry.
It seemed a reasonable compromise to add. Reverser interlocking shouldn't be difficult either, will think about that, and this some more.....

FWIW, the specific case I was thinking of here was some of the much more modern stuff (post microprocessor, I'd guess the past 20 odd years of designs), which now has hill-start buttons, as opposed to the original practice of holding on the brakes and applying power.

Whether there's actually physical interlocking in there WRT to the power handle, I don't actually know.

Normally these 3 primary interlocking algorithms are implemented purely mechanically.
Btw, think brake priority (whether train tries to apply power with brake handle not in 0) should be an option too

Never say never, but I'd be rather surprised to see a train with such interlocking. Not applying power if the brake handle isn't in 0 - yeah, sure, I can see that. There are even locomotives not applying power as long as there's pressure in the brake cylinder, e.g. some GDR-produced engines, unless the override button (used e.g. in inclines) is pressed; most notably class 143 and relatives. But physically blocking the handle from being moved, I don't think so.

Reverser interlocking on the other hand is pretty standard, especially on vehicles from before ~ 2000 (in Germany loco class 101 is the latest I know with this interlocking, built starting in 1996; and EMU class 411 the oldest without, built also starting in 1996). The power handle is locked in 0 with the reverser in 0 (and, where present, in M) and the reverser is blocked in its position with the power handle out of 0.

Reverser interlock added

(These are at least easy, and require no major internal plumbing to sort out)