Let me restate: for a game to specifically provide for telling a story in play, it must have mechanics that enforce that playstyle. What do those games do to do that? What player choices or actions are curtailed or prohibited, if any?
I'm not sure what you mean by "what player choices or actions are curtailed?" I mean, the most straightforward answer is
none. But presumably that's not the answer you're looking for?
In conventional D&D play, what sorts of actions are curtailed or prohibited? Well, if the rules tell you that your PC is dead, that affects permitted action declarations. Likewise if the rules tell you that your PC is paralysed, or trapped in an oubliette, or whatever.
Upthread I posted the rules for duels from Wuthering Heights. In those rules, if both duellists fail to role below their Rage then "they stop the duel and become friends, or something like that. They would not fight again for 1d10 days." So if the rules tell you that you're not fighting with someone anymore -that you become friends, or something like that - then that affects your permitted action declarations.
Consider again the PC trapped in the oubliette. Suppose the player declares, "I search for a secret way out." In conventional D&D play, the most important factor in determining whether or not the character succeeds in their attempt to find a secret way out is
what decision has the GM made about whether or not there is a secret way out of this oubliette. In Marvel Heroic RP, by way of contrast, there is no GM decision of that sort that is relevant to resolving the declared action: it is resolved by a roll against the Doom Pool (as augmented by any appropriate Scene Distinctions, such as (eg) No Way Out). In Burning Wheel, depending on further details no roll may be required for the PC to find a way out; but if a roll is required then again its outcome will not depend on a GM decision, but will depend upon the result of a roll on Perception or Secret Passage-wise or whatever skill(s) the player and GM agree is relevant to resolving the declared action.
Games have rules and procedures, and these determine what actions can be declared, how they are resolved, etc. Framing this in terms of "curtailment or prohibition" doesn't seem that helpful to me. That assumes some sort of baseline that doesn't exist, even as an ideal.
At minimum you need:
Some kind of organisational question which we’re answering
The principle that you are actually playing to find out what happens as it relates to the question
Attentiveness to the ethos of the characters involved
If you strip out the GM section of GURPS 4 and replace it with those principles, you’d get story orientated play. Well ok in practice you’d need to expand on those principles and probably offer some help setting up a situation but that’s the bare minimum required to distinguish it from a GURPS sandbox.
mechanics in and of themselves do nothing. It's the organising agenda that uses the mechanics that is the thing. Which is why the agenda and principles are so important, more so than the mechanics by far,
I agree with the last sentence. I think you are slightly understating what is required to get "story oriented play" out of GURPS. I'll admit I've never done it with GURPS, but I've done it with Rolemaster. And as well as agenda and principles of the sort that you point to, you also need to be ready to work around mechanics that are resolutely committed to foregrounding an ethos-neutral setting, rather than an ethos-laden situation.
Here's just one example of what I mean: Burning Wheel and Torchbearer 2e have a Circles mechanics, which is similar (not identical) across the two games. It permits a player to make a roll to have their PC encounter a friendly/useful/helpful NPC; the difficulty of the roll is set by a range of factors, including (but not limited to) the degree of the NPC's friendliness/usefulness/helpfulness. If the Circles roll is failed, the GM has a range of options as to how to narrate the failure, but one important one is to bring onto the scene a NPC who is hostile to the player's PC, or at a minimum is unhelpful or unfriendly in a way that foregrounds, but dashes, the hopes the PC had which the player was giving effect to by making the Circles roll.
Here's an example from actual play:
The session then focused predominantly upon Thoth. His Beliefs are I will give the dead new life; Aedhros is a failure, so I will bind him to my will; Cometh the corpse, cometh Thoth! And the player leaned heavily into these. Thoth also has a rather idiosyncratic pattern of speech - something of a lisp, and at least a hint of a European, perhaps German, accent.
Thoth wanted to go to the docks to find corpses, of those who had died at sea.
<snip>
A die of fate roll indicated that one corpse was available for collection, and Aedhros helped Thoth carry it off.
<snip>
Thoth successfully performed Taxidermy - against Ob 5 - to preserve the corpse, with a roll good enough to carry over +1D advantage to the Death Art test but did not what to attempt the Ob 7 Death Art (with his Death Art 5) until he could be boosted by Blood Magic. And so he sent Aedhros out to find a victim
Aedhros had helped collect the corpse, and also helped with the Taxidermy (using his skill with Heart-seeker), but was unable to help with the Death Art. He was reasonably happy to now leave the workshop; and was no stranger to stealthy kidnappings in the dark. I told my friend (now GMing) that I wanted to use Stealthy, Inconspicuous and Knives to spring upon someone and force them, at knife point, to come with me to the workshop. He called for a linked test first, on Inconspicuous with Stealth FoRKed in. This succeeded, and Aedhros found a suitable place outside a house of ill-repute, ready to kidnap a lady of the night. When a victim appeared, Aedhros tried to force a Steel test (I think - my memory is a bit hazy) but whatever it was, it failed, and the intended victim went screaming into the night. Now there is word on the street of a knife-wielding assailant.
Aedhros's Beliefs are I will avenge the death of my spouse!, Thurandril will admit that I am right! and I will free Alicia and myself from the curse of Thoth!; and his Instincts are Never use Song of Soothing unless compelled to, Always repay hurt with hurt, and When my mind is elsewhere, quietly sing the elven lays. Having failed at the most basic task, and not knowing how to return to Thoth empty-handed, Aedhros wandered away from the docks, up into the wealthier parts of the city, to the home of the Elven Ambassador. As he sang the Elven lays to himself, I asked the GM for a test on Sing, to serve as a linked test to help in my next test to resist Thoth's bullying and depravity. The GM set my Spite of 5 as the obstacle, and I failed - a spend of a fate point only got me to 4 successes on 4 dice.
My singing attracted the attention of a guard, who had heard the word on the street, and didn't like the look of this rag-clothed Dark Elf. Aedhros has Circles 3 and a +1 reputation with the Etharchs, and so I rolled my 4 dice to see if an Etharch (whether Thurandril or one of his underlings or associates) would turn up here and now to tell the guards that I am right and they should not arrest me. But the test failed, and the only person to turn up was another guard to join the first in bundling me off. So I had to resort to the more mundane method of offering them 1D of loot to leave me alone. The GM accepted this, no test required.
Then, repaying hurt with hurt, Aedhros followed one of the guards - George, as we later learned he was called - who also happened to be the one with the loot. Aedhros ambushed him from the darkness, and took him at knife point back to the workshop, where Thoth subject him to the necessary "treatment"
I've included the context leading up to the Circles roll, because it is important for seeing how the outcome of the Circles roll contributed to
story: Aedhros, who is a Dark Elf in the Tolkien-esque sense, is being bullied and dictated to by Thoth; he tries to abduct a woman, but fails; he then has the possibility of rising above this sordidness, first by Singing - but this fails, and so the GM narrates that a guard comes - and then the Circles attempt, to have Elves turn up and affirm Aedhros, also fails - and so the GM narrates another guard coming. And then, presented with this situation as a player, and playing my character, Aedhros falls back into sordidness - first bribing the guards, and then kidnapping one of them so that Thoth can perform Blood Magic on him.
Rolemaster (and I think this is also true of GURPS) has no analogue of the narration of Circles failure (or of Singing failure, for that matter): there's no provision for using the failed Streetwise or Etiquette or whatever test as a trigger for escalating the conflict across the moral line/question that is the focus of play. And so it's much harder to reliably get rising action culminating in climax/resolution.
@Reynard, this example should also answer some of your questions. There's no prohibition/curtailment of action declarations. But there are principles that govern how situations are established and how consequences are decided upon. This is what creates the
story, in the sense of protagonists in a situation of conflict, with rising action and climax/resolution.
Of course, in AD&D 2nd ed, the GM can narrate a guard turning up if they like. But there is no process to govern this - they can do it if the Sing check is successful, and they don't have to do anything if the Sing check fails other than narrate that Aedhros can't sing well today (which undercuts the sense of a
protagonist in a conflict, because it tends to make the characters look silly). Story won't result unless the GM decides that it will - which means that authorship of a story is required. That's not the case in Burning Wheel: the GM just has to follow the rules for how to narrate the consequence of a failed roll.
