diff --git a/packages/data-schemas/src/methods/auditLog.spec.ts b/packages/data-schemas/src/methods/auditLog.spec.ts
index f4f8a0c512..79344d4c03 100644
--- a/packages/data-schemas/src/methods/auditLog.spec.ts
+++ b/packages/data-schemas/src/methods/auditLog.spec.ts
@@ -69,6 +69,18 @@ describe('auditLog methods', () => {
       const raw = await AuditLog.collection.findOne({});
       expect(raw && Object.prototype.hasOwnProperty.call(raw, 'tenantId')).toBe(false);
     });
+
+    it('treats blank and whitespace-only tenantId as platform-level (no silent drop)', async () => {
+      const blank = await methods.recordAuditEntry(baseInput({ tenantId: '' }));
+      const whitespace = await methods.recordAuditEntry(baseInput({ tenantId: '   ' }));
+      expect(blank).not.toBeNull();
+      expect(whitespace).not.toBeNull();
+      const rows = await AuditLog.collection.find({}).toArray();
+      expect(rows).toHaveLength(2);
+      for (const row of rows) {
+        expect(Object.prototype.hasOwnProperty.call(row, 'tenantId')).toBe(false);
+      }
+    });
   });
 
   describe('listAuditLogPage', () => {
diff --git a/packages/data-schemas/src/methods/auditLog.ts b/packages/data-schemas/src/methods/auditLog.ts
index 487bacea86..1ac7d0cc16 100644
--- a/packages/data-schemas/src/methods/auditLog.ts
+++ b/packages/data-schemas/src/methods/auditLog.ts
@@ -120,6 +120,16 @@ function clampLimit(limit?: number): number {
 export function createAuditLogMethods(mongoose: typeof import('mongoose')): AuditLogMethods {
   async function recordAuditEntry(input: RecordAuditEntryInput): Promise<IAuditLog | null> {
     const AuditLog = mongoose.models.AuditLog as Model<IAuditLog>;
+    /**
+     * Match the read-side `tenantFilter` convention: blank or whitespace-only
+     * tenant IDs are platform-level scope and the field must be omitted
+     * entirely (so the row matches `{ tenantId: { $exists: false } }` queries
+     * and satisfies the non-empty-string validator on the schema).
+     */
+    const normalizedTenantId =
+      typeof input.tenantId === 'string' && input.tenantId.trim().length > 0
+        ? input.tenantId
+        : undefined;
     try {
       const doc = await AuditLog.create({
         action: input.action,
@@ -129,7 +139,7 @@ export function createAuditLogMethods(mongoose: typeof import('mongoose')): Audi
         targetPrincipalId: input.targetPrincipalId,
         targetName: input.targetName,
         capability: input.capability,
-        ...(input.tenantId != null && { tenantId: input.tenantId }),
+        ...(normalizedTenantId !== undefined && { tenantId: normalizedTenantId }),
       });
       return doc;
     } catch (err) {