Fix verification and immersion-tracker grouping

- isolate verifier artifacts and lease handling
- switch weekly/monthly tracker cutoffs to calendar boundaries
- tighten boot lifecycle and zip writer tests

src/core/services/immersion-tracker/maintenance.test.ts

@@ -8,6 +8,7 @@ import {
   pruneRawRetention,
   pruneRollupRetention,
   runOptimizeMaintenance,
+  toMonthKey,
 } from './maintenance';
 import { ensureSchema } from './storage';
 
@@ -81,6 +82,12 @@ test('pruneRawRetention uses session retention separately from telemetry retenti
   }
 });
 
+test('toMonthKey floors negative timestamps into the prior UTC month', () => {
+  assert.equal(toMonthKey(-1), 196912);
+  assert.equal(toMonthKey(-86_400_000), 196912);
+  assert.equal(toMonthKey(0), 197001);
+});
+
 test('raw retention keeps rollups and rollup retention prunes them separately', () => {
   const dbPath = makeDbPath();
   const db = new Database(dbPath);