# Sense

A `compute()` function that samples or derives external data. The only first-class citizen in nerve.

## Behavior

- Returns `T | null` — non-null emits a Signal, null is silent (no storage write, no signal, no downstream trigger)
- Each Sense has its own **independent SQLite database**
- Cross-sense reads are read-only via `peers` parameter
- Schema defined with Drizzle ORM (`schema.ts` is single source of truth)

## Sense → Workflow

If `compute()` returns an object with `workflow: "name|maxRounds|prompt"`, the engine starts that workflow and does **not** emit a Signal. `workflow: null` or `""` means emit signal normally.

See `routeSenseComputeOutput` / `parseSenseWorkflowDirective` in `@uncaged/nerve-core`.

## Config (nerve.yaml)

```yaml
senses:
  cpu-usage:
    group: system        # senses in same group share a worker
    throttle: 10s        # min interval between computes
    timeout: 30s         # max compute duration
    grace_period: 5s     # wait before first compute
    interval: 30s        # periodic trigger (optional)
    on: [disk-pressure]  # trigger on signals from other senses (optional)
```