Manbearcat
Legend
A complicating factor here is that AD&D doesn't really have an action resolution system! There's combat which has its own fairly detailed system; there are thief abiliites, which at least as presented are purely task resolution except perhaps hide in shadows; and there are some rules for dealing with doors and traps.
Fail forward depends on there being a player intent behind the action declaration, which the GM then draws upon to establish the failure. In AD&D, you might be able to use ability checks or similar to resolve actions and adjudicate them in a fail forward fashion - but this would be complicated by the pretty ad hoc gating of certain capabilities behind non-weapon proficiencies.
On this, I would say that AD&D 2e actually suffers from too many various forms of discrete action resolution (2 of which you've mentioned above) rather than a dearth of them. Accordingly, it does (naturally), suffer from a unified framework of action resolution. Simultaneously, (alluding to my post above), it suffers from a dearth of all the things I mentioned above that would lend coherency, intuitiveness for players, transparency, system-guided GM constraint, and systemitized PC protagonism! As such, this is why I would put it squarely on the opposite end of the GM Force spectrum from a game that properly leverages Fail Forward (such as Burning Wheel). The only use AD&D 2e would have for Fail Forward is as another vessel for the covert GM Force (Illusionism) that it promotes!
And a comment on GM-force: if the GM is providing the intent of the action (eg deciding what will be gained by opening a door, listening at a door, searching for a trap, etc; this goes back to [MENTION=99817]chaochou[/MENTION]'s post upthread) then success with complications tends to mean that the intent is realised but something bad accompanies it; and the "badness" is also a reflection of the GM's intent as to where the "plot" should go. You find the clue, but break your thieve's tools in doing so or You open the door, but make a loud noise.
I definitely agree with this. It hooks back into my premise above of. In order for Fail Forward to create interesting decision-points for the players (through the lens of their PCs) and emergent story trajectory for all participants (GM included) to be surprised by, the entire "system biosphere" needs to support that paradigm.
In terms of actual conversation at the table and machinery of play, that means precisely what you're describing above. What is at stake needs to be systemitized, verbally agreed upon, or completely intuitive for all participants. Player intent and resolution mechanics (rather than GM intent and heavy mediation in action resolution) needs to be the pivot point upon which the gamestate changes. If these things become obfuscated/non-intuitive to players due to opaque system machinery or circumvented by GM mandate (lack of systemitized GM constraint), the outcome becomes just another lever to pull to ration preconceived plot via "Illusionism" or "GM-sided plot control techniques" as [MENTION=99817]chaochou[/MENTION] put it above.