- The duration of Mist is very short, because you take force combat turns to cast it (because it being a permanent spell) and it can at maximum last also that long (with decreasing effect). Here it would make more sense to let this be a sustained spell with no decreasing effect.
It's not a permanent spell. It's a physical spell yes (Type P), but the duration is instant (Duration: I). So it doesn't take you any time to cast it other than the complex action. For a near identical spell regarding the statblock: Ice Sheet from the core book. Only the Drain is different. In both cases, the spell instantly creates the effect (after the complex action to cast it), and then the effect lasts depending on environmental conditions. No sustain, no long cast time.
And even then, I believe you may be misunderstanding how casting a permanent spell works. Unless it's Ritual Spellcasting,
all spells cast in one Complex Action. (Or Simple if you like drain.) In the case of Permanent spells, you sustain (not continue casting) for the Force duration in combat turns, with all attendant drawbacks to sustaining a spell. (Note that if you are familiar with SR3, there's no such thing an an exclusive spell/action anymore, so you can cast other spells while sustaining an existing spell for as long as you want..)
Permanent (P) spells don’t fade or dissipate; their effect becomes a lasting, non-magical characteristic after you sustain the spell for (Force) Combat Turns.
Bold mine. Now, if you think that it should be a sustained spell rather than an instant spell with a short duration, that's fine. But this doesn't exactly count as errata, because the spell isn't wrong.
- Can the spell “Reinforce” also be cast on vehicles?
Why wouldn't it? Given the restrictions, it appears to be mostly useful for small objects. (For various values of small.)
Though, good luck getting your Magic Rating high enough to be effective for a car. Magic Rating caps the area in square meters. Remember a square meter is 1x1 meter square. So half the windshield or a side window. A 3m x 3m square is actually 9 square meters. A full car bumper to bumper all the way around to include tires would be difficult to cover with PC Magic Rating.* Heck, Dragons would probably have a problem with it, though there might be an improved spell (in universe) that does a volume rather than surface area. So you'd need to be strategic with Reinforce, assuming your GM says that a window or a panel is an "object" not the car.
*
Surface area.
-Ariketh