…ESCRIPTION

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

…tion

`getSection({ guard, lift })` now requires an explicit interface guard,
mirroring how `makeExo` always requires one. `getGlobalSection({ lift })`
is the new convenience wrapper that computes the full union guard from
all presheaf sections, analogous to `makeDefaultExo`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

… dispatch

Replace string-log side-channels and return-value inference with explicit
vi.fn() spy assertions. Each section's handler is a named mock; tests call
expect(spy).toHaveBeenCalledWith(...) and .not.toHaveBeenCalled() to verify
routing directly rather than inferring it from coincident return values.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

…rg sections

`getGuardAt` was returning `undefined` for positions beyond a section's
fixed argument range, even when a `restArgGuard` was present. This caused
rest-arg sections to be absent from optional-position unions, producing
a false negative: e.g. `M.call().rest(M.string())` would not cover
position 0 in the union, so a call `['hello']` would fail the collected
guard even though the section accepts it.

Fix: fall through to `payload.restArgGuard` after exhausting the optional
array, so rest-arg sections contribute to every optional position in the
union.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Add MetaDataSpec<M> discriminated union (constant | source | callable) so
that sheaf metadata can vary with call arguments rather than being static.

- constant(v)   — static value, evaluated once
- source(s)     — JS source string compiled via Compartment at sheafify
                  construction time, called at dispatch time
- callable(fn)  — live function called at dispatch time

PresheafSection.metadata changes from M to MetaDataSpec<M> (breaking).
A new EvaluatedSection<M> type carries post-evaluation metadata and is
what Lift receives as its germs array.  EvaluatedSection is distinct from
PresheafSection because the "germ" in the sheaf-theoretic sense only
exists after quotienting by the metadata-equivalence relation (the
collapseEquivalent step); EvaluatedSection describes the pre-collapse
stage where the spec has been applied to the invocation args.

getStalk is generalised to <T extends { exo: Section }> so it works over
ResolvedSection (the internal post-resolution type) without a cast.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

- getStalk: accept readonly T[] to allow frozen section arrays
- evaluatedStalk map: omit metadata property when undefined to satisfy
  exactOptionalPropertyTypes (metadata?: M ≠ metadata: M | undefined)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>