perf: send a schema reference in get-block-data instead of the full schema

[vshvets-bc]

Problem

requestVcDocumentBlock and requestVcDocumentBlockAddon getData() embed the full schema (document + context) in every form block. For policies with large schemas the same schema is serialized once per form block, so get-block-data responses can reach tens of MB. That payload is JSON.parse/JSON.stringify-d as it is relayed between services (which do not read it), kept in memory on the client, and re-fetched on every block update — the repeated multi-MB serialization blocks the single Node event loop and slows unrelated requests.

Change

Emit a lightweight schema reference { id, iri, uuid, name, version } instead of the full document/context. The frontend resolves the full schema once by id (cached and de-duplicated) via the existing GET /schema/:id.

• Much smaller get-block-data responses for schema-heavy forms.
• Backward-compatible: the frontend uses a full schema (with document) exactly as before, so the client change is a no-op until the backend sends a reference. The change is sequenced so the frontend can ship first.

Details

• policy-service: request-vc-document-block.ts, request-vc-document-block-addon.ts — getData returns the reference.
• frontend: SchemaService.getSchemaById + cached/de-duplicated/error-evicting resolveSchemaById; request-document-block(-addon) _onSuccess resolves a reference to the full schema before the existing render flow.

Tests

• policy-service (new request-vc-getdata-reference.test.mjs): getData emits a reference, not document/context. Passing.
• frontend (new schema.service.spec.ts): endpoint, concurrent-subscriber de-dup, cache-hit, and error-eviction/retry.

Notes for reviewers

• The frontend package was not built in this environment; the policy-service change and its test build and pass.
• Worth confirming there is no non-frontend consumer of get-block-data that relies on the embedded document/context (e.g. remote/multi-policy interaction). The id/iri are still present for anything that needs to look the schema up.