fix: unify diagnostics history access

Resolve diagnostic history through the injected loadHistory dependency whenever it is available, retaining config history only for legacy collectors without a dedicated reader.

Build server_health error and batch summaries from one validated snapshot so migrated installations cannot combine current batches with stale errors or parse the external history twice.

Add focused regressions for migrated history consistency and fail-closed handling of invalid dedicated history results.

tests/diagnostics-collectors.test.js

@@ -86,6 +86,62 @@ test('getHistory falls back to loadConfig().history when loadHistory is absent (
   assert.equal(c.getHistory({ limit: 10 }).totalBatches, 1, 'legacy path reads load().history when loadHistory not injected');
 });
 
+test('getHistory, listErrors and serverHealth share loadHistory after migration', () => {
+  let historyRevision = 0;
+  const c = createCollectors({
+    loadConfig: () => ({ hosters: {}, globalSettings: {}, history: [] }),
+    loadHistory: () => {
+      historyRevision++;
+      const timestamp = `2026-01-${String(historyRevision).padStart(2, '0')}T00:00:00.000Z`;
+      return [{ timestamp, files: [{ name: `failed-${historyRevision}.mkv`, results: [{ hoster: 'voe.sx', status: 'error', error: 'Not video file format' }] }] }];
+    },
+    getAllLogPaths: () => ({ logDir: os.tmpdir() }),
+    support, stats,
+    appInfo: () => ({}), systemInfo: () => ({}), agentInfo: () => ({})
+  });
+  const health = c.serverHealth({ errorLimit: 5 });
+  const history = c.getHistory({ limit: 5 });
+  const errors = c.listErrors({ limit: 5 });
+  assert.deepEqual({
+    historyBatches: history.totalBatches,
+    listedErrors: errors.total,
+    healthBatches: health.recentBatches.length,
+    healthErrors: health.errors.total
+  }, {
+    historyBatches: 1,
+    listedErrors: 1,
+    healthBatches: 1,
+    healthErrors: 1
+  });
+  assert.equal(health.recentBatches[0].timestamp, health.errors.errors[0].ts, 'serverHealth must summarize one history snapshot');
+});
+
+test('history commands fail closed instead of reading stale config history', () => {
+  const c = createCollectors({
+    loadConfig: () => ({
+      hosters: {},
+      globalSettings: {},
+      history: [{ timestamp: '2025-12-31T00:00:00.000Z', files: [{ name: 'stale.mkv', results: [{ hoster: 'voe.sx', status: 'error', error: 'stale error' }] }] }]
+    }),
+    loadHistory: () => null,
+    getAllLogPaths: () => ({ logDir: os.tmpdir() }),
+    support, stats,
+    appInfo: () => ({}), systemInfo: () => ({}), agentInfo: () => ({})
+  });
+  const health = c.serverHealth({ errorLimit: 5 });
+  assert.deepEqual({
+    historyBatches: c.getHistory({ limit: 5 }).totalBatches,
+    listedErrors: c.listErrors({ limit: 5 }).total,
+    healthBatches: health.recentBatches.length,
+    healthErrors: health.errors.total
+  }, {
+    historyBatches: 0,
+    listedErrors: 0,
+    healthBatches: 0,
+    healthErrors: 0
+  });
+});
+
 test('readLog redacts a planted token and a Bearer line; doodstream is NOT readable; unknown name rejected', () => {
   const { collectors, dir, paths } = makeFixture();
   const dbg = collectors.readLog({ name: 'debug', tailKb: 64 });