fix: pass username through ts_authenticate for ai grading calls

Allows run_ai_grading to authenticate as the correct user rather than
always falling back to TEST_USER.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/e2e_quality.py

@@ -539,15 +539,16 @@ def _find_ts_key_for_url(ts_base_url: str) -> str:
     return os.getenv("TS_ENV_1_KEY_VAR", "")
 
 
-def ts_authenticate(ts_base_url: str) -> requests.Session:
+def ts_authenticate(ts_base_url: str, username: str = None) -> requests.Session:
     secret_key = _find_ts_key_for_url(ts_base_url)
     if not secret_key:
         raise RuntimeError(f"No trusted auth key found for {ts_base_url}")
+    auth_user = username or TEST_USER
     session = requests.Session()
     session.headers["Accept"] = "application/json"
     resp = session.post(
         f"{ts_base_url}/api/rest/2.0/auth/token/full",
-        json={"username": TEST_USER, "secret_key": secret_key, "validity_time_in_sec": 3600},
+        json={"username": auth_user, "secret_key": secret_key, "validity_time_in_sec": 3600},
         timeout=30,
     )
     resp.raise_for_status()
@@ -859,7 +860,7 @@ Return ONLY valid JSON:
 
 
 def run_ai_grading(run_context: dict, company: str, vertical: str, line: str, function: str,
-                   schema_override: str = None) -> dict:
+                   schema_override: str = None, username: str = None) -> dict:
     result = {
         "data_score": None, "data_points": 0.0,
         "data_reasoning": "Not graded", "data_strengths": [], "data_weaknesses": [],
@@ -877,7 +878,7 @@ def run_ai_grading(run_context: dict, company: str, vertical: str, line: str, fu
         return result
 
     try:
-        session = ts_authenticate(ts_base)
+        session = ts_authenticate(ts_base, username=username)
     except Exception as e:
         result["grading_errors"].append(f"ThoughtSpot auth failed: {e}")
         return result