Enforced mechanisms hold work to intent across later changes. Constrain first so the wrong move is unavailable; where prevention falls short, a sensor catches the drift.

ConceptBig idea 4 · Thesis 2

Hold intent with a mechanism: prevent first, sense the rest

Two forms a quality goal splits into: a constraint or a sensor A quality goal you want to hold splits into two moves — prevent the mistake, or catch it — however you arrived at the goal, up front from the domain or in response to a failure. On the left, a constraint: it makes the whole class of mistake impossible by scoping the action space, like choosing a typed enumeration over free-form strings so an unlisted value cannot be represented, like a firewall. On the right, a sensor: it lets the mistake happen but detects it and surfaces it in time to stop the damage, like a test suite in CI or a smoke detector. The wall forbids the bug; the sensor watches for it. The wall is cheaper to live behind than the sensor is to keep reading. Quality goal prevent the mistake, or catch it Constraint — prevents Makes the whole class of mistake impossible. typed enum over strings · firewall Sensor — detects Lets the mistake happen, detects it before it ships. test suite in CI · smoke detector

Engineering intuition

A type the compiler checks, a lint that blocks the commit, a gate that refuses the deploy: each holds a policy decided once against every later change. Costly goals earn both a constraint and a sensor; what neither reaches stays a human job.

Related concepts

Mechanisms

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