On a related note: how do people normally deal with the patrolling watcher or low-force spirit that's just there to die and so the mage can trigger the alarm?
That was actually the genesis of my OP, I was hoping a particular reading of banishing would allow for a way to get past a spirit set to guard the only reasonably accessible way into a room without alerting the summoner. As it stands now, if a single entrance is the only way in somewhere and a spirit is guarding it, stealth is pretty much out.
Even with more than a single entrance, it can be tough. With how fast someone in the astral can move, even while still being able to pay attention to things, a single spirit can glance over a number of entrances every turn. Outside of an initiative order, that can mean you have much less than a second to cross the threshold and get out of the spirit's sight. And that's assuming it's "astrally walking" at 100 meters per combat turn, not astrally running (which doesn't seem to imply it'd be fatiguing at all) at 5 kilometers per turn. The spirit might get kinda bored, but their job is easy... "Look" for glowing things on a field of gray that weren't there before and mention it. You don't need to be the most attentive to pull it off, since they can't really hide...
Since there's no way to just
not show up on the astral, the only thing I could think of would be either figuring a loophole in the spirit's command ("I was told to report people, not drones.") and use that to take out the mage, or to somehow bargain with it, both of which I feel would be the GM handing you a cookie because both seem things that should not be common among security mages at all.
If it weren't for the telepathic link, I'd say trapping the spirit in a mana barrier would work, but... Well, the link exists so that won't work. Even the most robotic and literal spirit is aware enough to realize being trapped in a bubble is something they should mention to their summoner. They
are fully sentient after all. And purely logically, it would prevent them from doing them from doing their owed service, and would be something they'd want to get out of... And if they can't (that'd be the idea of using the spell in the first place), asking their summoner for help seems like the most natural response.