Propagation

What happens when a failed value meets an operator? The failure wins, and keeps its story:

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bad = int['oops']
worse = bad + 10
log[worse.ok]
log[worse.reason]

false
cannot convert 'oops' to int

No crash, no exception — bad + 10 is simply another error value with the original reason. Arithmetic, interpolation, function calls: pass a failure through any of them and it propagates unchanged, appending to .trace as it crosses function boundaries.

This is the quiet radicalism of the model: the code between where a failure happens and where it's handled doesn't participate. No ? on every call, no try blocks around every section, no exception specifications. Intermediate code stays written for the happy path, and failures flow through it inert — they only matter when something tries to make a decision with one. Which is the next section.