refactor(audience): move SESSION_START/SESSION_END constants to core

Both the SDK and pixel use these event names — they belong in
@imtbl/audience-core so both surfaces import from one place.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ImmutableJeffrey

packages/audience/core/src/config.ts

@@ -17,4 +17,7 @@ export const SESSION_COOKIE = '_imtbl_sid';
 export const COOKIE_MAX_AGE_SECONDS = 365 * 24 * 60 * 60 * 2; // 2 years
 export const SESSION_MAX_AGE = 30 * 60; // 30 minutes in seconds
 
+export const SESSION_START = 'session_start';
+export const SESSION_END = 'session_end';
+
 export const getBaseUrl = (environment: Environment): string => BASE_URLS[environment];

packages/audience/core/src/index.ts

@@ -34,6 +34,8 @@ export {
   COOKIE_NAME,
   SESSION_COOKIE,
   SESSION_MAX_AGE,
+  SESSION_START,
+  SESSION_END,
 } from './config';
 
 export { generateId, getTimestamp, isBrowser } from './utils';

packages/audience/sdk/src/config.ts

@@ -10,11 +10,3 @@ export const LOG_PREFIX = '[audience]';
 
 /** Default consent source when consentSource is not provided in config. */
 export const DEFAULT_CONSENT_SOURCE = 'WebSDK';
-
-// --- Auto-tracked event names ---
-// These are fired by the SDK lifecycle, not by studio code.
-
-/** Fired on init (or consent upgrade from none) when no active session cookie exists. */
-export const SESSION_START = 'session_start';
-/** Fired on explicit shutdown(). Not fired on tab close or consent revocation. */
-export const SESSION_END = 'session_end';

packages/audience/sdk/src/sdk.test.ts

@@ -1,8 +1,8 @@
 import {
-  COOKIE_NAME, SESSION_COOKIE, INGEST_PATH, CONSENT_PATH,
+  COOKIE_NAME, SESSION_COOKIE, INGEST_PATH, CONSENT_PATH, SESSION_START, SESSION_END,
 } from '@imtbl/audience-core';
 import { Audience } from './sdk';
-import { LIBRARY_NAME, SESSION_START, SESSION_END } from './config';
+import { LIBRARY_NAME } from './config';
 
 // --- Test fixtures ---
 const TEST_USER = { uid: 'user@example.com', provider: 'email' } as const;

packages/audience/sdk/src/sdk.ts

@@ -26,11 +26,13 @@ import {
   collectAttribution,
   getOrCreateSession,
   createConsentManager,
+  SESSION_START,
+  SESSION_END,
 } from '@imtbl/audience-core';
 import { DebugLogger } from './debug';
 import type { AudienceConfig } from './types';
 import {
-  LIBRARY_NAME, LIBRARY_VERSION, LOG_PREFIX, DEFAULT_CONSENT_SOURCE, SESSION_START, SESSION_END,
+  LIBRARY_NAME, LIBRARY_VERSION, LOG_PREFIX, DEFAULT_CONSENT_SOURCE,
 } from './config';
 
 /**