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LDC-E2402 — An unknown computability class in the annotation

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# LDC-E2402 — An unknown computability class in the annotation

## What it means

The computability annotation accepts only the fixed list of known
classes, from fully pure to non-executable. A class name outside that
list names nothing the compiler can check a body against — it is most
often a misspelling. The compiler refuses the annotation at the annotation
itself, and lists the classes it accepts.

The fix is a spelling correction: pick the intended class from the list
the message carries. Known classes outside lower-bound inference and annotations on unsupported
subjects report LDC-W2404 instead of silently passing.

## Example

```law
language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

relation seen(x: Integer) kind empirical;
@expected_computability("BOGUS_CLASS")
relation marked(x: Integer) kind institutional;
```

## Fix

```law
language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

relation seen(x: Integer) kind empirical;
@expected_computability("PURE_DETERMINISTIC")
relation marked(x: Integer) kind institutional;
```

## Engine message

The engine reports this in its own wording:

```text
example.law:6:1: error LDC-E2402: @expected_computability("BOGUS_CLASS"): unknown class §47.5
```

## Related

- [Expressions and quantities](/constructs/expressions-quantities/) — what function bodies may compute.