How does a Demon detect a Linchpin?

Question

All God-Machine Infrastructure has a Linchpin. The Linchpin doesn't have to be tied by human logic to what the infrastructure does, thought there is often some symbolism or anti-logic to it.

Some examples of infrastructure in the book:

• An underground facility has three obelisks above it: one hides the air vents, one hides the power conduits, and one is just solid brick like it looks. The solid brick one is the linchpin.
• A bridge is infrastructure. Its linchpin is the pay-phone booth on the end.

Now in the sample adventure in the back of the book, it seems clear that demons can at least work out what the linchpin is, though not at a glance. However I can't find the rules to determine how it is done.

It is debatable whether infrastructural can be permanently destroyed without destroying the linchpin (or using a super-natural; ability like Destroy Infrastructure). It is quiet likely that any damage that doesn't destroy the linchpin can be repaired without requiring a new Occult Matrix to form it.

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If there are no rules given, I lean towards a house rule like:

If you have Aesthetic Resonance active, then you may as a extended action, 1 minute/roll (longer for larger infrastructure), roll Wits + Science + Primum − penitences for concealment infrastructure, etc., to determine which part of the infrastructure is allowing it to work beyond the laws of known science.

Answer 1

Demons detect Linchpins on sight or, more remotely, through analysis.

The Demon Quickstart (released before the core book) states, "Demons can always recognize Linchpins for what they are." (p.50) Unfortunately, this wasn't mentioned in the core book.

The rule is repeated almost exactly, however, in Flowers of Hell: "They can recognize a Linchpin for what it is." (p. 72) That whole section (p.72-74), entitled Analyzing Infrastructure, is likely the exact system that you're looking for. It provides rules that allow a demon to discover details of an Occult Matrix (such as Linchpin/s) through an extended action to scrutinize some component Infrastructure. The example of play has a line, "Thanks to her demonic nature, she knows on sight that the stamp is the Linchpin." which seems to soundly demonstrate that demons do, in fact, know Linchpins "at a glance," but might have to do some normal investigation or use the analysis rules if they aren't immediately perceivable.

Answer 2

There are no rules to my knowledge, however the new book Flowers of Hell may explain more

Flowers of Hell: The Demon Players Guide expands on the material presented in Demon: The Descent, with additional information on the Agendas, the Unchained condition and mindset, and how the reason for the Fall – the catalyst – affects game play and character development. You’ll also find rules for suborning Infrastructure and what kinds of risks and rewards it brings.

Emphasis mine.