What it means for the screen to stay on the screen
This is the only card on the map with no software in it. The condition is a fact about a room: whether the light coming off the screen reaches anybody other than you. Nothing here is a setting, and nothing here can be checked by a program.
The obvious version is a person standing behind you, and it is not the common one. The common versions are duller. A desk positioned so the screen faces an open door, a walkway or a window. A shared table where two people work at right angles and each can see most of the other's display. Glass behind you that returns a legible reflection after dark, which surprises people who have never looked. A screen sharing session somebody started for a meeting and nobody ended, still duplicating the display in another room. A phone lying on the desk with its camera pointing up.
What is at risk is specific. Not your identity or your habits, but the literal contents of the screen while they are on it: a long string of characters, a name chosen to be used nowhere else, a phrase shown once and never again, a postal address in full. Each has value only while one party holds it, and each appears on screen at some point in this chain.
A second card with nothing standing behind it
This is a root, like The machine is one you actually control, and for a different reason. That card is a root because ownership of a machine cannot be decomposed further. This one is a root because the map has no vocabulary for rooms. The site is a graph of technical conditions, and a doorway is not one of them.
Roots and endings describes roots as the points where the map hands the problem back to you, and here the handover is total. There is no configuration that improves a sightline, no verification step that closes a door, and no upstream card whose repair would repair this one as a side effect. If it is false, it stays false until you move a desk, close a door, turn a screen, or wait until the room is empty.
The chain that stops at a doorway
One card depends on this one: The browser doing this does nothing else. That card is about separation. The window used for this must not be the window signed in to the rest of your life, because a browser holding both joins them in history, in sessions and in whatever a page can reach.
The room defeats that separation from outside the machine, and the mechanism is worth stating precisely. Software separation works by ensuring no single component sees both sides. A person in the room is a single component that sees both sides. They watch you work in one window and then in the other, and the join is made in their memory rather than in any file. The browser did its job and the outcome is the same as if it had not. A mirroring session behaves identically, duplicating every window regardless of which one you consider separate.
That card also carries The browser came from the Tor Project and The security level was set before the first page loaded among its conditions, and neither helps here. Provenance and security level govern what the software does. They say nothing about who is standing in the room while it does it, which is why this exists as a separate root rather than as a note on the browser stage.
The separation card is terminal, so the chain below this one is short. That does not make it cheap. Everything that card exists to prevent happens anyway, without leaving anything behind that you could later inspect.
| What is on the screen | What a second reader gets from it |
|---|---|
| A long address string | A destination they hold, and a subject they know you are interested in. |
| An account name | A name searchable anywhere else it has appeared. |
| A phrase shown once at registration | The recovery material in full, with no way to revoke the viewing. |
| A postal address on an order form | A place, attached to everything else already visible. |
How a room gets away with it
Skip this one and you will most likely never find out. That is what makes the card unusual. Every other condition on the map fails in a way that eventually produces a symptom: a page that will not load, a login that will not take, a parcel that does not arrive. This one produces nothing. There is no log, no error and no notification. The screen looked the same to you whether or not it was also visible from the doorway.
When it does surface, it surfaces socially and late. A remark lands that only makes sense if a screen was read. By then the reading happened weeks ago, and nothing can be established about what was on the screen or how much of it was legible. If this is false treats this as the extreme case of a general pattern: the further a condition sits from any output, the later its failure is noticed.
Standing in the other person's place
The check is physical and takes less than a minute. Work out where the most likely other person would actually be. Not an intruder, but whoever does in fact walk past: a colleague, someone in the household, a stranger at the next table. Go and stand there, and look at the screen from that position and that angle.
A pass is that the text is not readable from there. Shapes and colours are fine. Individual characters are not. A fail is that you can read a line of it, which is likelier than people expect with a bright screen in a dim room. Do it once after dark as well, facing whatever glass is behind you, because the same room can pass by day and fail at night.
The other half is the viewer you cannot see. Check that no screen sharing or mirroring session is running and what the machine is connected to for display. That is a setting rather than a sightline, but the effect is identical and it survives closing the door. Words used here defines the terms.
One fact about a room, not a threat model
This is not a threat model. It is a single narrow physical fact, and the only physical fact on this map. It is not the software separation described on the browser card, which closes a different join, and it is not the question of who administers the machine. A room can be private on a machine you do not control, and a machine you fully control can sit in a room with a glass wall.