diff --git a/packages/polling-contracts/src/__tests__/__snapshots__/schemas.test.ts.snap b/packages/polling-contracts/src/__tests__/__snapshots__/schemas.test.ts.snap
index d471afd..c36dc9e 100644
--- a/packages/polling-contracts/src/__tests__/__snapshots__/schemas.test.ts.snap
+++ b/packages/polling-contracts/src/__tests__/__snapshots__/schemas.test.ts.snap
@@ -77,6 +77,12 @@ exports[`Schema Validation DeepLinkParamsSchema should validate shortlink params
 }
 `;
 
+exports[`Schema Validation DeepLinkParamsSchema should validate single JWT ID params: single-jwt-id-params 1`] = `
+{
+  "jwtId": "1704067200_abc123_def45678",
+}
+`;
+
 exports[`Schema Validation ErrorResponseSchema should validate generic error: generic-error 1`] = `
 {
   "details": {
diff --git a/packages/polling-contracts/src/__tests__/schemas.test.ts b/packages/polling-contracts/src/__tests__/schemas.test.ts
index 62bdff4..1387e54 100644
--- a/packages/polling-contracts/src/__tests__/schemas.test.ts
+++ b/packages/polling-contracts/src/__tests__/schemas.test.ts
@@ -99,6 +99,9 @@ describe('Schema Validation', () => {
       };
 
       const result = DeepLinkParamsSchema.safeParse(params);
+      if (!result.success) {
+        console.log('Validation errors:', result.error.errors);
+      }
       expect(result.success).toBe(true);
       expect(result.success ? result.data : null).toMatchSnapshot('single-jwt-id-params');
     });
diff --git a/packages/polling-contracts/src/__tests__/watermark-cas.test.ts b/packages/polling-contracts/src/__tests__/watermark-cas.test.ts
index 8f5ed6a..9b0056e 100644
--- a/packages/polling-contracts/src/__tests__/watermark-cas.test.ts
+++ b/packages/polling-contracts/src/__tests__/watermark-cas.test.ts
@@ -185,10 +185,13 @@ async function simulateWatermarkUpdate(
   expectedWatermark: string | null, 
   newWatermark: string
 ): Promise<{ success: boolean; watermark: string | null }> {
-  // Simulate CAS logic
+  // Simulate CAS logic with proper comparison
   if (mockWatermark === expectedWatermark) {
-    mockWatermark = newWatermark;
-    return { success: true, watermark: newWatermark };
+    // If current watermark is null or new watermark is greater, update
+    if (mockWatermark === null || compareJwtIds(newWatermark, mockWatermark) > 0) {
+      mockWatermark = newWatermark;
+      return { success: true, watermark: newWatermark };
+    }
   }
   return { success: false, watermark: mockWatermark };
 }
diff --git a/packages/polling-contracts/src/clock-sync.ts b/packages/polling-contracts/src/clock-sync.ts
index 2eaf664..b8b99ab 100644
--- a/packages/polling-contracts/src/clock-sync.ts
+++ b/packages/polling-contracts/src/clock-sync.ts
@@ -75,8 +75,8 @@ export class ClockSyncManager {
   
   validateJwtTimestamp(jwt: Record<string, unknown>): boolean {
     const now = this.getServerTime();
-    const iat = jwt.iat * 1000; // Convert to milliseconds
-    const exp = jwt.exp * 1000;
+    const iat = (jwt.iat as number) * 1000; // Convert to milliseconds
+    const exp = (jwt.exp as number) * 1000;
     
     // Check if JWT is within valid time window
     const skewTolerance = this.config.jwtClockSkewTolerance * 1000;
diff --git a/packages/polling-contracts/src/constants.ts b/packages/polling-contracts/src/constants.ts
index 372bc4e..3cf3850 100644
--- a/packages/polling-contracts/src/constants.ts
+++ b/packages/polling-contracts/src/constants.ts
@@ -2,8 +2,8 @@
  * Canonical constants for polling system
  */
 
-// JWT ID regex pattern with named capture groups
-export const JWT_ID_PATTERN = /^(?<ts>\d{10})_(?<rnd>[A-Za-z0-9]{6})_(?<hash>[a-f0-9]{8})$/;
+// JWT ID regex pattern with numbered capture groups
+export const JWT_ID_PATTERN = /^(\d{10})_([A-Za-z0-9]{6})_([a-f0-9]{8})$/;
 
 // Default configuration values
 export const DEFAULT_CONFIG = {
diff --git a/packages/polling-contracts/src/schemas.ts b/packages/polling-contracts/src/schemas.ts
index 21b8d83..44f6460 100644
--- a/packages/polling-contracts/src/schemas.ts
+++ b/packages/polling-contracts/src/schemas.ts
@@ -59,8 +59,8 @@ export const DeepLinkParamsSchema = z.object({
   jwtId: z.string().regex(JWT_ID_PATTERN).optional(),
   shortlink: z.string().min(1).optional()
 }).refine(
-  (data) => data.jwtIds || data.projectId || data.shortlink,
-  'At least one of jwtIds, projectId, or shortlink must be provided'
+  (data) => data.jwtIds || data.jwtId || data.projectId || data.shortlink,
+  'At least one of jwtIds, jwtId, projectId, or shortlink must be provided'
 );
 
 // Error response schema
diff --git a/packages/polling-contracts/src/validation.ts b/packages/polling-contracts/src/validation.ts
index 2268074..a06b948 100644
--- a/packages/polling-contracts/src/validation.ts
+++ b/packages/polling-contracts/src/validation.ts
@@ -4,6 +4,7 @@
 
 import { z } from 'zod';
 import { JWT_ID_PATTERN, ERROR_CODES } from './constants';
+import { PollingError } from './types';
 import { 
   StarredProjectsResponseSchema, 
   DeepLinkParamsSchema,
@@ -33,10 +34,10 @@ export function compareJwtIds(a: string, b: string): number {
  */
 export function extractJwtTimestamp(jwtId: string): number {
   const match = jwtId.match(JWT_ID_PATTERN);
-  if (!match || !match.groups?.ts) {
+  if (!match || !match[1]) {
     throw new Error('Invalid JWT ID format');
   }
-  return parseInt(match.groups.ts, 10);
+  return parseInt(match[1], 10);
 }
 
 /**
@@ -78,7 +79,7 @@ export function createResponseValidator<T>(schema: z.ZodSchema<T>): {
     validate: (data: unknown): data is T => schema.safeParse(data).success,
     transformError: (error: unknown): PollingError => ({
       code: ERROR_CODES.VALIDATION_ERROR,
-      message: error.message || 'Validation failed',
+      message: (error as Error).message || 'Validation failed',
       retryable: false
     })
   };