`agnes query --remote` corrupted user SQL when the request contained a
full BigQuery backtick path (`<project>.<dataset>.<table>`) whose
table segment matched a registered bare-name alias. The bare-name
rewriter used `\b` word-boundary matching against the lower-cased SQL;
both `.` and `` ` `` are non-word characters, so the regex fired
INSIDE the user's backtick path and produced malformed nested-backtick
SQL that BigQuery rejected at parse time.
Fix:
- Add `_mask_backticks(sql)` helper: replace each `…` segment with
spaces of equal length, preserving offsets so word-boundary
searches find positions only outside backticks.
- `_bq_guardrail_inputs` (bare-name pass + forbidden-table pass)
searches against the masked SQL.
- `_rewrite_bq_table_refs_to_native` Pass 1 splits the SQL on
`(\`[^\`]*\`)` and rewrites only the outside-backtick chunks. Pass
2 (`bq."ds"."tbl"` → backtick form) is unchanged — its prefix can't
appear inside backticks.
Adds three regressions covering the rewrite + guardrail paths.
720a2180c0