translate_bq_error previously mapped BQ's responseTooLarge failure mode
to bq_bad_request (HTTP 400 with the raw upstream message). The user-
facing implication ('your SQL has a syntax error') is wrong -- the root
cause is query shape (BQ refused to return the result inline because
it exceeded the response size limit), and the actionable remediation is
'narrow the WHERE clause, aggregate further, or use a materialized
table'.
Add bq_response_too_large as a first-class BqAccessError kind (also 400)
with a canonical hint message; original BQ message preserved in details
for operator debugging. Detection is substring-based on 'response too
large' and fires before the generic BadRequest path so the dedicated
mapping always wins. Affects every BQ-touching path since they all
share translate_bq_error -- /api/query, /api/v2/{scan,sample,schema},
materialize.
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