sec(query): #160 BQ_PATH catches quoted "bq" catalog token (Phase 3 review)

Phase 3 review identified an RBAC + cost-cap bypass: `SELECT * FROM
"bq"."ds"."tbl"` (catalog token quoted as a DuckDB identifier) was NOT
matched by the BQ_PATH regex, so direct quoted-form references skipped
both the registry check and the cost-cap dry-run. DuckDB resolves
`"bq"` to the same ATTACHed BQ catalog, so the bypass is real.

Widen the catalog-token alternation: `(?:"bq"|bq)` matches both forms.
Negative lookbehind `(?<![\w.])` still rejects look-alike prefixes
(`other_bq`, `my_bq`); the new "my_bq".ds.tbl negative test locks that
in alongside `other_bq.ds.tbl`.

Tests:
- 2 new positive cases in tests/test_query_bq_regex.py for the quoted
  form (`"bq"."finance"."ue"` and uppercase `"BQ"."ds"."tbl"`).
- 1 new negative case rejecting `"my_bq".ds.tbl` so the quoted-form
  widening doesn't open a different evasion.
- 1 new RBAC test in tests/test_api_query_rbac_bq_path.py: admin
  hitting an unregistered quoted path returns the same
  bq_path_not_registered 403 as the unquoted form.

All 33 Phase 3 tests pass after the fix.

app/api/query.py

@@ -31,12 +31,16 @@ logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/api/query", tags=["query"])
 
 # Issue #160 §4.3.1 — direct `bq.<dataset>.<source_table>` references in user
-# SQL. Matches all 16 cases verified empirically (fully-quoted, unquoted,
-# mixed quoting, case-insensitive, inside CTE bodies, multiple in one stmt).
+# SQL. Catalog token accepts both `bq` (the unquoted DuckDB-style name) and
+# `"bq"` (quoted identifier). DuckDB resolves both to the same ATTACHed
+# catalog, so the security-boundary regex must accept both — Phase 3 review
+# caught the quoted variant as an RBAC + cost-cap bypass.
 # Lookahead `(?=\W|$)` works where `\b` doesn't (after a closing quote).
-# Negative lookbehind `(?<![\w.])` rejects `other_bq.x.y` and `x.bq.y.z`.
+# Negative lookbehind `(?<![\w.])` rejects `other_bq.x.y`, `my_bq.ds.tbl`,
+# and `x.bq.y.z` so the regex doesn't fire on column qualifiers or
+# look-alike-prefixed identifiers.
 BQ_PATH = re.compile(
-    r'(?<![\w.])bq\s*\.\s*("[^"]+"|\w+)\s*\.\s*("[^"]+"|\w+)(?=\W|$)',
+    r'(?<![\w.])(?:"bq"|bq)\s*\.\s*("[^"]+"|\w+)\s*\.\s*("[^"]+"|\w+)(?=\W|$)',
     re.IGNORECASE,
 )
 

tests/test_api_query_rbac_bq_path.py

@@ -36,6 +36,24 @@ def _register_bq_remote_row(name: str, bucket: str, source_table: str) -> None:
         sys_conn.close()
 
 
+def test_quoted_bq_catalog_token_rejected_403(seeded_app):
+    """Phase 3 review evasion: `SELECT * FROM "bq"."ds"."tbl"` (catalog
+    token quoted) must be caught by the same RBAC check as the unquoted
+    form. DuckDB resolves `"bq"` to the same ATTACHed BQ catalog, so the
+    quoted variant is a real bypass we have to close."""
+    c = seeded_app["client"]
+    token = seeded_app["admin_token"]
+    r = c.post(
+        "/api/query",
+        json={"sql": 'SELECT * FROM "bq"."secret_ds"."secret_tbl"'},
+        headers=_auth(token),
+    )
+    assert r.status_code == 403, r.json()
+    detail = r.json().get("detail", {})
+    if isinstance(detail, dict):
+        assert detail.get("reason") == "bq_path_not_registered", detail
+
+
 def test_unregistered_bq_path_rejected_403(seeded_app):
     """Direct reference to a `bq.<ds>.<tbl>` that no registry row points at:
     403 with `bq_path_not_registered`. Caller has admin token (no per-name

tests/test_query_bq_regex.py

@@ -25,6 +25,9 @@ def regex():
     ('SELECT * FROM bq.finance."ue"', ('finance', '"ue"')),
     # Case-insensitive
     ('select * from BQ.Finance.UE', ('Finance', 'UE')),
+    # Quoted catalog token "bq" — Phase 3 review evasion: must be caught
+    ('SELECT * FROM "bq"."finance"."ue"', ('"finance"', '"ue"')),
+    ('SELECT * FROM "BQ"."ds"."tbl"', ('"ds"', '"tbl"')),
     # With WHERE
     ('SELECT a FROM bq.ds.tbl WHERE x=1', ('ds', 'tbl')),
     # Inside CTE body
@@ -55,6 +58,7 @@ def test_regex_finds_multiple_paths_in_one_statement(regex):
     ('SELECT bq.col FROM tbl', '2-part bq.col is column qualifier, not catalog'),
     ('SELECT count(*) FROM unit_economics', 'aggregate on bare name'),
     ('SELECT * FROM other_bq.ds.tbl', 'prefix that contains bq'),
+    ('SELECT * FROM "my_bq".ds.tbl', 'quoted prefix that contains bq'),
     ('SELECT * FROM x.bq.ds.tbl', 'bq is middle component, not catalog'),
 ])
 def test_regex_rejects_non_bq_paths(regex, sql, reason):