Problem

ValidateRequestAndResponseIds parsed the request id (via IdFromRawMessage, which only accepts string/number/null) before reaching its existing "null/empty response id" carve-out. So when a client sends a non-scalar id (object/array) — invalid per JSON-RPC 2.0 — lavap hard-fails with failed parsing ID …, which surfaces to the consumer as jsonRPC ID mismatch error → failed relay, insufficient results and triggers a cross-provider retry storm, even when the relay itself was fine.

Observed in production on Polygon: a .NET client serialized a CancellationToken into the id:

{"IsCancellationRequested":false,"CanBeCanceled":false,"WaitHandle":{"Handle":{"value":6404},...}}

Captured against live nodes, the two react differently — and both were being failed:

• Polygon rejects the object id and replies id:null (correct per spec).
• NEAR accepts it, returns a valid result, and echoes the object id back — which lavap then discarded.

This is chain-agnostic: the same failure reproduces on any chain (confirmed by sending an object id to both gateways).

Fix

• Reorder: evaluate the null/empty/[] response-id carve-out first, before parsing the request id (covers Polygon's id:null rejection — the node's own invalid request now passes through instead of a retry storm).
• Semantic fallback: when either id is non-scalar, compare the ids by value (tolerant of whitespace / object key order) instead of erroring (covers NEAR's verbatim echo, preserving the valid response). A genuinely different id is still reported as a mismatch.
• Scalar-id behaviour is unchanged.

The root cause is a non-compliant client (an object id violates JSON-RPC 2.0); this change makes lavap surface the node's real response instead of masking it behind an internal "ID mismatch".

Verification

• New regression test TestValidateRequestAndResponseIds_NonScalarId: proven to fail without the change with the exact production error (failed parsing ID … not a string or float (id: {…CancellationToken…})) and pass with it. Covers Polygon (object→null), NEAR (object echo), whitespace tolerance, genuine object mismatch, and unchanged scalar cases.
• Full chainlib suite + go build / go vet / gofmt clean.

Relationship to #2301

Separate root cause from #2301 (NEAR UNKNOWN_BLOCK classification). This PR addresses the Polygon-reported failure; the two are independent and touch different code paths.

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