Unfortunately I seem to have drawn your focus to matters that relate to "Different RPGs set different rules for what the players are allowed to tell us about their characters; and for what the GM is allowed to tell us about the situation/context" but that are
peripheral to the comments of mine that you were responding to.
My post aimed to draw attention, solely, to the technical meaning of the term "fiction" as it appears in for e.g. "
The fiction matters." Whereas,
@pemerton rightly advanced concepts such as "
shared imagination" and (of participants)
"how they contribute to the fiction and
how they engage with the fiction" I wanted to add a specific technical definition.
1. Consider another poster's comment about "getting the magic lamp, based on what is relevant to the
story". Historically, and perhaps even today for most folk, a "story" is a prescripted linear narrative. One can have a prescripted linear narrative of a chess game just as readily as one can have a prescripted linear narrative of a band of heroes encountering a lich. This possible definition of fiction is worth having in mind in contrast to the technical definition of fiction that fits the OP's theory.
2. What's described in 1. clearly encompasses recipients of a prescripted linear narrative, and can be extended to include the relater of a prescripted linear narrative. This definition of fiction still does not fit OP's theory.
3. The "fiction" that fits the OP's theory is a technical feature distinct to RPG's that Vincent Baker labelled "fictional positioning." (I spell that out for others who might not be aware of his
2012 discussions.) It has properties that are critical to roleplaying. As you and the OP called out, it must be addressable by the participants during play. Much is made of divisions of authority, but the crucial feature is
ongoing authorship of a common fiction, through a continuous process of drafting and revising, that all participate in. (Notice the way in which the foregoing wording recognises solo-RPG as RPG!)
That has a multitude of vital consequences for RPG, and up to here the OP is on solid ground that I believe isn't really in dispute. Notwithstanding, a technical term I propose we have in mind relating to that word "fiction" coming right after "ongoing" is "
fictional position" as that makes it more accurate and meaningful.