I think we're pretty close to the same page here, Lion.
By bulky, I meant "having bulk(i.e. volume) or mass" not necessarily restrictive. I intended to imply something that would be hard to fit additional trappings over.
I'm of a similar mind to your definition, with the caveat that I'd say it would have to cover the trunk and limbs to qualify as "full-body."
You're on target as far as dry suits(which is more of a cold water set-up) or deep water gear go. I only mentioned dive gear because the dive armor in R&G is described as an armored wetsuit, which wouldn't be an impermeable barrier against a contact vector. It'd probably make it worse, actually.
Lethal nerve agents are canonically part of MCT zero-zones, it's something of a signature for them, but that is an extreme security measure (and specifically called out as warranting extra hazard pay) and, you're right, most runs are unlikely to have to deal with poison gas. Tear gas, on the other hand, can reasonably be standard issue for a corp-sec guard at a secure facility (it is in at least one of the fiction pieces in R&G, for example). A gas mask is a sufficient precaution, chem-seal would be another option.
I'd even argue the presence of tear gas. It's a pretty pervasive, if temporary, gas and it's pretty indiscriminate. I've got a bit of long post coming, so I'll try to be as brief as I can.
I believe that the corps have a scale of security and enforcement. That the average guard has a radio with some sort of alarm functionality, a side arm, baton and maybe an armoured vest. They're designed to look good and advertise this area is under observation. They don't need to wear a formal uniform, but it helps.
Above them I see an armed response team, submachine guns, shotguns, heavier armour than the door guards, but not full combat armour. They've got a little more kit to play with as well, customised weapons, flashbangs, but still not tear gas. They're there to respond to a breach and to lock it down as fast as possible. They're also first responders in the case of emergencies as well, fires, medical, Runners etc.
Within the previous listed group, I imagine a riot control squad, these guys are the first guys to see proper combat armour and tear gas. This is for when mass units, mobs are attacking and need to be discouraged, not killed. This about a statement of force that we could have killed you, we've got the potential to kill you, but we're being nice. This is a specialised role that is only called in specific and I'd argue rare circumstances. Sure, they might get sent up against a Runner team, but it will be part of a plan to delay them and force them into an ambush.
Above them I'm starting to see direct combat units, who are specialised for direct combat. This is where you have corporate soldiers and special forces. This is where the level of force is always lethal. Bonuses are paid for making sure all of a team gets out of alive and all of the Runners targeted are dead, two extra in the brainpan just to be sure. These people are wearing high grade armour, high grade weapons, specialised training in order to be more dangerous than the average bear.
I'd argue that depending on the level of security the facility calls for, you go straight from 'we're being nice' to 'kill them all'. There's certain levels you go to protect secrets. I'd also argue that certain personnel are going to be protected. Tear gas makes it much harder to identify and remove those key personnel from a combat area. Adding in a visual obstruction and one that also serves to disable them? It doesn't make sense on some level. So, when you've got everyone out, sure, throw a few grenades of tear gas. Yet if you're stuck running on visual confirmation of a hostile and a friendly, why do you sabotage that?
Sure, yes, tear gas is used, I don't think it is as pervasive in use as people think. It's a pretty nasty tool to use and more importantly it's only one of many. Normal smoke, flash bangs, I'd argue those are much more common and to a degree, when used by people with training, represent a significant threat and can be just as effective as tear gas, without the nausea. Basic tactics are often all a good team needs. Coming in on the flanks, ambushing a team as they try to move. All of those can be done without tear gas.
I think a part of is that role players are taking a very.... gamer centric point of view to the game. That if you can be prepared for something, you over prepare for it. If I as a player can chem seal my armour, I'm going to do all my Runs in it. Game masters then I suppose feel the need to use it, gases, toxins, poisons, as often as they can and try to catch people off guard so that they can hit them with things like tear gas, or in the case of MCT Zero Zones, something a little more dangerous.
On the same side I believe that a good Runner makes sure that there's little reason for the lethal force to come out. Yes, you can kill everyone in your way, including the unfortunate wage slaves who are working late. The other option is to have a plan and be nice about it. Yes, point a few guns, tie a few people up, maybe even fake a few alarms to distract security. Go full hog and cut power to the building as well.
Now tell me, as a high level corp manager, which would you go after first? Would you think about recruiting the low foot print team?
Good to see we're on the same page on a few elements here.
I could go with providing protection for the limbs as well. I'm still not too sure on it, while I appreciate the threats of the Sixth World, there's also something to be said for the fact that full military/corporate grade armour is going to be easy to get or commonly needed. I think that between the respirators, gas masks and survival bubble, there's plenty of options to protect yourself against chemical threats. To be honest I think if every Runner has a respirator or a gas mask, they're set. Going to the extent of a full Chem Seal armour, that's a statement of intent on your part, not just dealing with a threat.
See the above question about the low foot print team. If I see a guy wearing full armour with it being Chem Sealed, I'm more than happy to assume that they are willing to drop a cannister of tear gas themselves, or worse. Otherwise why are they are wearing that level of protection as well? You're asking to be marked as a target, which means you might not survive as long as you otherwise might.
If I had to narrow down to a single definition now, I would say that Full Body Armour is one that coverages a significant portion of the body, upwards of seventy percent. This includes notable protection over the limbs, neck and torso. Front and back, in addition it should also provide the tools to assist in long term combat. Webbing and the like here. I would also argue a limit on the amount of component customisation, but be very easily visually customised, camouflage.