[ohmayr]

Context & Problem

createQueryArrowStream turned a record batch that arrived without a schema into an empty RecordBatch, silently dropping its rows. The skip has been on main since #9596, so this fixes it on its own, outside the Arrow stack.

Summary of Changes

• decodeArrowPayload throws Got an Arrow record batch before its schema. when it gets batch bytes without a schema, matching the Python client (fix(bigquery): raise when an Arrow batch arrives before its schema google-cloud-python#18791).
• Responses with neither a schema nor a batch (for example DDL/DML) still yield one 0-column RecordBatch.

Verification

• New unit test for an inline jobs.query response with arrowRecordBatch but no arrowSchema; it fails without the fix.
• pnpm test in handwritten/bigquery: 551 passing.
• GIT_DIFF_ARG=origin/main node ./bin/linter.mjs --strict: no problems.

[gemini-code-assist]

Code Review

This pull request updates the decodeArrowPayload function to throw an error if an Arrow record batch is received without its schema, preventing rows from being silently dropped, and adds a corresponding test case. The review feedback recommends checking that serializedRecordBatch is present and has a length greater than 0 to ensure consistent truthiness handling between empty strings and empty Uint8Arrays.

[gemini-code-assist]

Checking serializedRecordBatch directly for truthiness can lead to inconsistent behavior because an empty string ("") is falsy, whereas an empty Uint8Array (new Uint8Array(0)) is truthy. To ensure consistent handling of empty payloads, check that serializedRecordBatch is both present and has a length greater than 0.

Suggested change

	if (serializedRecordBatch) {
	throw new Error('Got an Arrow record batch before its schema.');
	}
	if (serializedRecordBatch && serializedRecordBatch.length > 0) {
	throw new Error('Got an Arrow record batch before its schema.');
	}

[ohmayr]

Applied in 8f1679a. An empty payload has no rows to drop, so it now takes the same path as a missing one for both string and Uint8Array, matching Python's if batch_bytes:. Added a test for an empty Uint8Array without a schema.