gate-check

1# Find the gates
2 
3Theory: [Cheap decisions](https://secondbrainos.dev/#/read/course-3-gate/cheap-decisions)
4and [Gate practice](https://secondbrainos.dev/#/read/course-3-gate/gate-practice).
5An agent does two kinds of work: it writes, which needs a big model, and it
6decides — is this spam, which queue, does this need a person — which is a
7bounded question the answer to which comes from a set you already know.
8A gate is a cheap decision layer that sorts the stream so the expensive
9model only sees the items that actually need judgement.
10 
11## Workflow
12 
131. **Map the decisions.** Read the pipeline's entry points and prompts and
14   list every decision made before or during a model call: classification,
15   routing, filtering, yes/no triage, priority, language, "is this even for
16   us". Ignore the writing — only bounded decisions with a known label set.
172. **Count what each costs today.** For each decision currently made by the
18   big model: calls per day if known, tokens per call, and what a wrong
19   answer costs. A decision worth one bit that burns a frontier call is the
20   headline finding.
213. **Propose the cheapest gate that can hold it**, in rising order of cost:
22   - a **rule** — regex, allowlist, header check: free, instant, blind to
23     anything unanticipated; always the first layer, never the last
24   - a **classic classifier** — logistic regression or similar over simple
25     features, trained on a few hundred labelled examples: milliseconds,
26…