What separates the three layers is the write path, not the kind of question they ask.

# What separates the three layers is the write path, not the kind of question they ask.

A **Thread is
canon**. A **Stream stages a change to canon** and terminates in a Merge. A **Position never writes to
canon** — it is composed forward (Graph → Reading) and re-priced for as long as its question is live. All
three may hang on an outcome question; only a Stream's settling changes the model, and only a Position
carries a horizon and a monitor. *When the choice between them is unclear: open a **Stream** if you want the
evidence folded into the expert; open a **Position** if you want a read maintained and re-priced.*

The **Program** maintains all three. We keep the read current; the user does the deciding and the living —
the machine reads the world and re-prices, it never does the thinking for the user.

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