test(mcp): retry brief fetch on network errors + --brief-file escape hatch

Venue WiFi/proxy flaps were killing the burn-in with SSL errors before the
first build even fired. Fetch now retries 5x with backoff and fails with a
clear message; --brief-file runs the same brief from a local snapshot when
Supabase is unreachable.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/mcp_repeat_test.py

@@ -43,18 +43,32 @@ def log(msg: str) -> None:
     print(f"[{time.strftime('%H:%M:%S')}] {msg}", flush=True)
 
 
-def fetch_latest_brief(company: str) -> tuple[str, str, str]:
-    rows = (
-        SupabaseSettings().client.table("demo_history")
-        .select("company_name,use_case,results,created_at")
-        .eq("status", "mcp_intake")
-        .ilike("company_name", f"%{company}%")
-        .order("created_at", desc=True)
-        .limit(1)
-        .execute()
-        .data
-        or []
-    )
+def fetch_latest_brief(company: str, attempts: int = 5) -> tuple[str, str, str]:
+    rows = None
+    for attempt in range(1, attempts + 1):
+        try:
+            rows = (
+                SupabaseSettings().client.table("demo_history")
+                .select("company_name,use_case,results,created_at")
+                .eq("status", "mcp_intake")
+                .ilike("company_name", f"%{company}%")
+                .order("created_at", desc=True)
+                .limit(1)
+                .execute()
+                .data
+                or []
+            )
+            break
+        except Exception as e:
+            # Venue WiFi / proxy flaps surface here as SSL or connect errors;
+            # retry rather than dying before the first build is even fired.
+            if attempt == attempts:
+                raise SystemExit(
+                    f"Supabase unreachable after {attempts} attempts ({type(e).__name__}: "
+                    f"{str(e)[:160]}). Check network/proxy, or pass --brief-file."
+                )
+            log(f"brief fetch failed ({type(e).__name__}), retry {attempt}/{attempts - 1} in 10s")
+            time.sleep(10)
     if not rows:
         raise SystemExit(f"No mcp_intake brief for {company!r} in demo_history")
     row = rows[0]
@@ -129,6 +143,8 @@ def main() -> None:
     ap.add_argument("--company", default="Tixr")
     ap.add_argument("--owner", default="jack.rayner@thoughtspot.com")
     ap.add_argument("--timeout-min", type=int, default=30, help="per-run timeout")
+    ap.add_argument("--brief-file", help="read the brief from a local file instead of Supabase "
+                                         "(use when the network can't reach Supabase)")
     args = ap.parse_args()
 
     ep = os.getenv("MCP_ENDPOINT", H.DEFAULT_ENDPOINT)
@@ -136,7 +152,11 @@ def main() -> None:
     if not tok:
         raise SystemExit("MCP_ACCESS_TOKEN not set (env or demoprep_mcp/.env)")
 
-    brief, use_case, brief_ts = fetch_latest_brief(args.company)
+    if args.brief_file:
+        brief = open(args.brief_file).read()
+        use_case, brief_ts = "Event Ticketing Analytics", f"file:{args.brief_file}"
+    else:
+        brief, use_case, brief_ts = fetch_latest_brief(args.company)
     log(f"{args.company} brief from {brief_ts} | use_case={use_case!r} | len={len(brief)}")
     log(f"Running {args.count}x sequentially against {ep}")