fix: prevent stale capacity poisoning and deepen recent-only refill scans

Keep ordinary capacity races from lowering persistent per-account limits.
Deepen recent-only discovery within the existing age and quality gates.
Add offline regressions for recovery and reserved-slot refill.

modelhub_submmit_api/main.py

@@ -822,6 +822,17 @@ def build_adaptive_scan_stages(
                 "limit": max_models,
             }
         )
+    if not allow_older_than_recent_window:
+        # Reserved positions still need a deep search of eligible recent
+        # models. Widening the date window alone repeatedly scans the same
+        # short prefix (often already processed) on every poll cycle.
+        stages.append(
+            {
+                "name": "recent_window_full",
+                "updatedAfter": recent_cutoff,
+                "limit": max_models,
+            }
+        )
     deduped: list[dict[str, Any]] = []
     seen: set[tuple[str | None, int, str]] = set()
     for stage in stages: