feat(iiif-validator): add IIIF Presentation Manifest validator

[ddeboer]

What

Adds @lde/iiif-validator, a small, dependency-light package that validates whether a URL dereferences to a valid IIIF Presentation Manifest.

import { validateManifest } from '@lde/iiif-validator';

const verdict = await validateManifest('https://example.org/manifest.json');
// { valid: true, reason: 'valid-manifest' } | { valid: false, reason: 'http-error' | … }

Why

A reusable building block for Linked Data tooling that needs to tell a declared IIIF manifest apart from one that actually resolves and parses. The first consumer is the Dataset Knowledge Graph, which moves IIIF conformance from declared to validated by dereferencing a sample of manifest URIs per dataset. IIIF is an international standard with no NDE specifics, so the verifier belongs here, as a sibling to distribution-probe / distribution-downloader.

Behaviour

• Dereference over HTTP with Accept: application/ld+json, application/json, following redirects, using the global fetch with an AbortSignal timeout (default 10 000 ms). Both are injectable (fetch, timeoutMs).
• Lightweight, version-aware structural check. HTTP 2xx, body parses as JSON, @context references an IIIF Presentation context, and type/@type indicates a manifest — accepting v3 (Manifest) and v2 (sc:Manifest). @context may be a string, array, or object. The version segment is accepted version-agnostically.
• Strict failure semantics, no retries. Timeout, network error, non-2xx, unparseable body, missing IIIF @context, or wrong type all yield valid: false with a coarse reason. No deep JSON Schema validation, no dependency on the hosted IIIF Presentation Validator service.
• Never throws. Every outcome is a ManifestValidation verdict.

Tests

Unit-tested through the public interface with an injected fake fetch (no network): v3 / v2 manifests, @context as string / array / object, and each failure reason (http-error, timeout, network-error, invalid-json, not-a-manifest).