diff --git a/packages/spec/src/data/validation.test.ts b/packages/spec/src/data/validation.test.ts
index fd3b368218..128a8a1d73 100644
--- a/packages/spec/src/data/validation.test.ts
+++ b/packages/spec/src/data/validation.test.ts
@@ -736,8 +736,7 @@ describe('ValidationRuleSchema (Discriminated Union)', () => {
         type: 'custom' as const,
         name: 'custom_business_rule',
         message: 'Custom validation failed',
-        field: 'business_field',
-        validatorFunction: 'validateBusinessRule',
+        handler: 'validateBusinessRule',
       };
 
       expect(() => ValidationRuleSchema.parse(customValidation)).not.toThrow();
@@ -748,8 +747,7 @@ describe('ValidationRuleSchema (Discriminated Union)', () => {
         type: 'custom' as const,
         name: 'complex_validation',
         message: 'Validation failed',
-        field: 'data',
-        validatorFunction: 'complexValidator',
+        handler: 'complexValidator',
         params: {
           threshold: 100,
           mode: 'strict',
@@ -764,7 +762,7 @@ describe('ValidationRuleSchema (Discriminated Union)', () => {
         type: 'custom' as const,
         name: 'record_level_check',
         message: 'Record validation failed',
-        validatorFunction: 'validateEntireRecord',
+        handler: 'validateEntireRecord',
       };
 
       expect(() => ValidationRuleSchema.parse(validation)).not.toThrow();
@@ -1058,7 +1056,7 @@ describe('ValidationRuleSchema (Discriminated Union)', () => {
           type: 'custom',
           name: 'business_logic',
           message: 'Business logic validation failed',
-          validatorFunction: 'validateBusinessRules',
+          handler: 'validateBusinessRules',
         },
         {
           type: 'conditional',
@@ -1212,8 +1210,7 @@ describe('ValidationRuleSchema - Edge Cases and Null Handling', () => {
       type: 'custom' as const,
       name: 'custom_validation',
       message: 'Validation failed',
-      field: undefined, // Optional for record-level validation
-      validatorFunction: 'validateRecord',
+      handler: 'validateRecord',
       params: undefined,
     };
 
@@ -1225,7 +1222,7 @@ describe('ValidationRuleSchema - Edge Cases and Null Handling', () => {
       type: 'custom' as const,
       name: 'custom_validation',
       message: 'Validation failed',
-      validatorFunction: 'validateRecord',
+      handler: 'validateRecord',
       params: {},
     };
 
@@ -1339,7 +1336,7 @@ describe('ValidationRuleSchema - Type Coercion Edge Cases', () => {
         type: 'custom' as const,
         name: 'custom_test',
         message: 'Test',
-        validatorFunction: 'validate',
+        handler: 'validate',
         params,
       };
 
diff --git a/packages/spec/src/hub/tenant.zod.ts b/packages/spec/src/hub/tenant.zod.ts
index fd411afac2..a2df74988f 100644
--- a/packages/spec/src/hub/tenant.zod.ts
+++ b/packages/spec/src/hub/tenant.zod.ts
@@ -48,9 +48,66 @@ export const TenantQuotaSchema = z.object({
 
 export type TenantQuota = z.infer<typeof TenantQuotaSchema>;
 
-// Tenant Schema REMOVED.
-// The concept of a "Tenant" is now an attribute of a "Space".
-// See HubSpaceSchema in space.zod.ts which embeds TenantIsolationLevel and TenantQuotaSchema.
+/**
+ * Tenant Schema
+ * 
+ * @deprecated This schema is maintained for backward compatibility only.
+ * New implementations should use HubSpaceSchema which embeds tenant concepts.
+ * 
+ * **Migration Guide:**
+ * ```typescript
+ * // Old approach (deprecated):
+ * const tenant: Tenant = {
+ *   id: 'tenant_123',
+ *   name: 'My Tenant',
+ *   isolationLevel: 'shared_schema',
+ *   quotas: { maxUsers: 100 }
+ * };
+ * 
+ * // New approach (recommended):
+ * const space: HubSpace = {
+ *   id: '...uuid...',
+ *   name: 'My Tenant',
+ *   slug: 'my-tenant',
+ *   ownerId: 'user_id',
+ *   runtime: {
+ *     isolation: 'shared_schema',
+ *     quotas: { maxUsers: 100 }
+ *   },
+ *   bom: { ... }
+ * };
+ * ```
+ * 
+ * See HubSpaceSchema in space.zod.ts for the recommended approach.
+ */
+export const TenantSchema = z.object({
+  /**
+   * Unique tenant identifier
+   */
+  id: z.string().describe('Unique tenant identifier'),
+  
+  /**
+   * Tenant display name
+   */
+  name: z.string().describe('Tenant display name'),
+  
+  /**
+   * Data isolation level
+   */
+  isolationLevel: TenantIsolationLevel,
+  
+  /**
+   * Custom configuration values
+   */
+  customizations: z.record(z.any()).optional().describe('Custom configuration values'),
+  
+  /**
+   * Resource quotas
+   */
+  quotas: TenantQuotaSchema.optional(),
+});
+
+export type Tenant = z.infer<typeof TenantSchema>;
 
 /**
  * Tenant Isolation Strategy Documentation