fix: reload authoritative host health history

Refresh host health from the persisted retention-filtered history after batch completion, allowing the existing generation guard to reject stale responses and removing the competing local merge path.

lib/stats.js

@@ -39,23 +39,6 @@
     return out;
   }
 
-  function mergeHosterHealthHistory(history, batch) {
-    if (!Array.isArray(history)) return history;
-    if (!batch?.id) return [...history, batch];
-    const merged = [];
-    let replaced = false;
-    for (const existing of history) {
-      if (existing?.id === batch.id) {
-        if (!replaced) merged.push(batch);
-        replaced = true;
-      } else {
-        merged.push(existing);
-      }
-    }
-    if (!replaced) merged.push(batch);
-    return merged;
-  }
-
   function summarizeHosterHealth(history, options = {}) {
     const out = {};
     const hosters = options.hosters && typeof options.hosters === 'object' ? options.hosters : {};
@@ -297,7 +280,6 @@
 
   const api = {
     summarizePerHoster,
-    mergeHosterHealthHistory,
     summarizeHosterHealth,
     classifyErrorCategory,
     summarizeBatchErrors,