Run the snapshot rebuild before charts prewarm, not after

backend/app/routers/runs.py

@@ -1187,20 +1187,12 @@ def _run_refresh_cycle() -> None:
         _cyc0 = time.time()
         logger.info("refresh cycle: starting (leader)")
 
-        # Warm the /charts page FIRST so the default no-filter view of each chart
-        # is in Redis within seconds of a deploy, instead of waiting behind the
-        # entity-stats snapshot walk below (which can run for minutes). Frame
-        # charts warm immediately; blob charts that still need the snapshot come
-        # back "building" and re-warm on the next cycle. One worker, shared cache.
-        try:
-            if app_cache.enabled():
-                from .charts import prewarm_charts
-
-                prewarm_charts()
-        except Exception:
-            logger.warning("charts prewarm failed", exc_info=True)
-        logger.info("refresh cycle: charts prewarm done at %.1fs", time.time() - _cyc0)
-
+        # The entity-stats snapshot rebuild below is the critical product data
+        # (tier list / Codex Score / metrics), so it runs FIRST and nothing may
+        # starve it. Charts prewarm — which loads the full ~740k-run frame from
+        # Mongo and can run long under DB load — is deferred to the END of the
+        # cycle. This reverses PR #567's ordering: putting prewarm first let it
+        # block the snapshot rebuild indefinitely, so the snapshot never advanced.
         try:
             refresh_stats_summary()
         except Exception:
@@ -1251,6 +1243,19 @@ def _run_refresh_cycle() -> None:
         except Exception:
             logger.warning("entity-scores cache warm failed", exc_info=True)
 
+        # Charts prewarm LAST — it loads the full run frame from Mongo and can run
+        # for a while under load, so it must never delay the snapshot rebuild
+        # above. Trade-off: /charts warms a bit later after a deploy; the snapshot
+        # actually completing is the priority.
+        try:
+            if app_cache.enabled():
+                from .charts import prewarm_charts
+
+                prewarm_charts()
+        except Exception:
+            logger.warning("charts prewarm failed", exc_info=True)
+        logger.info("refresh cycle: charts prewarm done at %.1fs", time.time() - _cyc0)
+
     threading.Thread(target=_loop, daemon=True, name="stats-refresher").start()