Add four new Starlark sandbox builtins to reduce extension friction
around SQL decomposition and synchronous HTTP fan-out:
- db.count(table, filters) — integer row count
- db.aggregate(table, column, op, filters) — single-value aggregation
- db.query_batch(queries) — up to 10 query specs in one call
- http.batch(requests) — concurrent dispatch of up to 10 HTTP requests
Extract buildSelectQuery helper from dbQuery for reuse by query_batch.
21 new tests (14 db, 7 http). No new permissions or schema changes.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
