# Belief

The nervous system does not hand raw readings to consciousness and call them
truth. Evidence becomes belief through time, confidence, agreement, and source
health. Only a meaningful change becomes notable, and only authority turns a
notable belief into action.

The generic contract is in `src/core/nervous/belief.rs`; the first regional
implementation is `src/core/nervous/plexus.rs`.

## The ladder

Keep five layers separate:

1. **event** — something reported a sample or edge;
2. **evidence** — the sample with source, time, health, and quality;
3. **belief** — the organism's decaying, conflict-aware estimate;
4. **notable event** — a change worth waking another layer for;
5. **action** — a decision made by the owning authority.

A sensor is an actor, not an authority. A recognizer may say that two taps fit
a pattern. It does not decide that the body should wake. A plexus may believe
charge is falling. It does not independently suspend the machine.

## `Belief<T>`

A belief carries:

- an optional value;
- confidence;
- trend;
- persistence;
- observation time and half-life;
- contributing sources and conflicts.

Unknown is represented by no value. It is not observed zero, false, still, or
empty. As evidence ages, confidence decays. When healthy sources disagree, the
belief records conflict and loses confidence; it does not silently crown the
newest or loudest source as truth.

Trend and persistence describe change across time rather than another reading
of the same instant. This lets the body distinguish an edge, a sustained
condition, and a stale condition without pushing every sample upward.

## Exudates and gauges

The body has two different temporal shapes.

An exudate is a field that accumulates from impulses and dissipates. Touch,
motion, proximity, ambient light, and attendedness have this form. `Field`
integrates them and decays their value.

A gauge is a held reading whose value remains what was last observed while
confidence decays. Charge, thermal pressure, USB port mode, and future grip
values have this form. `Level` implements that shape inside the plexus.

Making both a single decaying scalar would tell two lies: an untouched field
would stay permanently excited, or a battery would drift toward zero merely
because the sensor had gone quiet.

## Locus and regulation

A field is either at the `Boundary` or `Inner { regulator }`.

Boundary fields describe contact and relation at the edge of the body. Inner
fields can threaten viability, so each must name its regulator. The type shape
prevents an inner pressure with no answer to "what can change it?"

Inner fields may carry floor or ceiling constraints. Crossing them creates
allostatic pressure: not an instruction or a mood, but the accumulating cost of
holding the body away from viability. The regulator remains an available verb,
not an automatic commandment.

## Source health

Expected sources can be live, silent, or absent. Recovery and silence are
themselves notable transitions because the meaning of the same value changes
when its evidence path dies.

The device-state machine and `SomaticPlexus` currently have adjacent
source-health concepts rather than one shared Rust type. Their doctrine is the
same—silence is not zero—but the duplication is current code and must not be
papered over in the architecture.

## Notability

`SomaticEvent` names the edges worth carrying upward: trend shifts, a source
going silent or recovering, and a viability boundary being threatened. The
plexus also compares a field's change against its own grade and persistence.

The goal is not to hide the body. It is to keep a 1 Hz clock or a noisy sensor
from masquerading as thought. Gauges remain inspectable at any time through the
body surface; the nervous path wakes other work only for meaningful change.

`NervousNode` is the common regional contract: receive evidence, advance on a
clock, expose beliefs, and emit notable events. The phone somatic plexus is the
first implementation, not a claim that every device and virtual organ already
speaks it.

## What is true, and what is not

Built and in sessiond:

- generic belief, decay, trend, persistence, conflict, and source provenance;
- exudate fields and gauge levels;
- boundary and regulated-inner loci;
- viability floors and ceilings with allostatic pressure;
- expected-source health and notable health transitions;
- a `NervousNode` implementation for the phone somatic plexus;
- tests for unknown versus zero, disagreement, gauges versus exudates,
  regulation, health, trend, and viability.

Not yet one coherent whole:

- device-state belief and somatic belief still have parallel structures;
- explicit impulse and intention types do not yet sit above belief;
- not every sensor family has a regional plexus;
- the event bus is still lossy and must not be mistaken for the durable belief
  or forensic store.

Belief is an estimate the organism can inspect. It is neither model prose nor a
permission to act.
