diff --git a/ENVIRONMENT_VARIABLES_AND_SECRETS.md b/ENVIRONMENT_VARIABLES_AND_SECRETS.md
index 1da1650..4f52741 100644
--- a/ENVIRONMENT_VARIABLES_AND_SECRETS.md
+++ b/ENVIRONMENT_VARIABLES_AND_SECRETS.md
@@ -33,6 +33,8 @@ The Rust smart contracts in `contract/` contain no runtime environment variables
 
 The listener is the only service with server-side secrets. All variables below are read from `process.env` in `listener/src/config.ts` (and supporting files) at startup.
 
+Variables marked **Required** are checked by `validateRequiredEnvVars()` in `listener/src/config.ts` before the rest of the config is loaded. If any are missing, `loadConfig()` throws a `ConfigError` listing every missing variable and the process exits instead of starting with an invalid configuration.
+
 ### 2.1 Logging / runtime
 
 | Variable | Default | Required | Description |
@@ -52,7 +54,7 @@ The listener is the only service with server-side secrets. All variables below a
 
 | Variable | Default | Required | Description |
 |---|---|---|---|
-| `CONTRACT_ADDRESSES` | `[]` | **Yes** (for any useful work) | JSON array of contract objects to monitor. See shape below. |
+| `CONTRACT_ADDRESSES` | *(none — enforced at startup)* | **Yes** | JSON array of contract objects to monitor. Missing this variable prevents the listener from starting; see note above. |
 
 **Shape:**
 ```json
diff --git a/listener/package.json b/listener/package.json
index ab17054..498caf2 100644
--- a/listener/package.json
+++ b/listener/package.json
@@ -11,8 +11,6 @@
     "test": "node ./node_modules/jest/bin/jest.js",
     "migrate": "ts-node src/scripts/migrate-db.ts",
     "migrate:templates": "ts-node src/scripts/migrate-templates.ts",
-    "typecheck": "node ./node_modules/typescript/bin/tsc --noEmit",
-    "lint": "node ./node_modules/typescript/bin/tsc --noEmit",
     "check-migrations": "ts-node src/scripts/check-migrations.ts",
     "validate:batch": "ts-node src/utils/batch-validator.ts"
   },
diff --git a/listener/src/__tests__/integration.test.ts b/listener/src/__tests__/integration.test.ts
index b3a6d1b..6aacadc 100644
--- a/listener/src/__tests__/integration.test.ts
+++ b/listener/src/__tests__/integration.test.ts
@@ -51,4 +51,29 @@ describe("Full Notification Lifecycle Integration Test", () => {
     // 5. Simulate acknowledgement (event is processed)
     expect(retrievedEvents[0].receivedAt).toBeLessThanOrEqual(Date.now());
   });
+
+  test("evicts oldest events instead of failing when registry is at capacity", () => {
+    const boundedRegistry = new EventRegistry(2);
+    const topic = [xdr.ScVal.scvSymbol("task"), xdr.ScVal.scvSymbol("created")];
+    const value = xdr.ScVal.scvU32(1);
+
+    for (let i = 0; i < 3; i++) {
+      boundedRegistry.addFromInput({
+        eventId: `event-${i}`,
+        contractAddress: "CDNJ3YJ5F4U5YF4O5U6Y7I8U9Y0U1I2O3P4I5U6Y7I8",
+        eventName: "task",
+        ledger: 100 + i,
+        type: "contract",
+        topic,
+        value,
+        txHash: `hash-${i}`,
+      });
+    }
+
+    // The registry should degrade gracefully (evict oldest) rather than
+    // throwing or silently dropping the newest notification.
+    const remaining = boundedRegistry.getEvents();
+    expect(remaining.length).toBe(2);
+    expect(remaining.map((e) => e.eventId)).toEqual(["event-1", "event-2"]);
+  });
 });
diff --git a/listener/src/config.test.ts b/listener/src/config.test.ts
index aaf3670..ccbce80 100644
--- a/listener/src/config.test.ts
+++ b/listener/src/config.test.ts
@@ -5,6 +5,9 @@ describe('Config validation', () => {
 
   beforeEach(() => {
     process.env = { ...originalEnv };
+    // CONTRACT_ADDRESSES is a required variable; give it a valid default so
+    // tests unrelated to required-variable validation aren't affected.
+    process.env.CONTRACT_ADDRESSES = JSON.stringify([{ address: 'CTEST', events: ['*'] }]);
   });
 
   afterEach(() => {
@@ -36,6 +39,15 @@ describe('Config validation', () => {
     expect(() => loadConfig()).toThrow('CONTRACT_ADDRESSES must be valid JSON. Received: not-json');
   });
 
+  it('throws a descriptive error when a required environment variable is missing', () => {
+    delete process.env.CONTRACT_ADDRESSES;
+
+    expect(() => loadConfig()).toThrow(ConfigError);
+    expect(() => loadConfig()).toThrow(
+      'Missing required environment variable(s): CONTRACT_ADDRESSES.'
+    );
+  });
+
   it('throws a descriptive error for invalid integer variables', () => {
     process.env.EVENTS_API_PORT = 'eighty';
 
@@ -44,9 +56,9 @@ describe('Config validation', () => {
   });
 
   it('loads default values when optional environment variables are omitted', () => {
+    process.env.CONTRACT_ADDRESSES = JSON.stringify([{ address: 'CTEST', events: ['*'] }]);
     delete process.env.STELLAR_NETWORK;
     delete process.env.STELLAR_RPC_URL;
-    delete process.env.CONTRACT_ADDRESSES;
     delete process.env.POLL_INTERVAL_MS;
     delete process.env.MAX_RECONNECT_ATTEMPTS;
     delete process.env.RECONNECT_DELAY_MS;
@@ -64,7 +76,7 @@ describe('Config validation', () => {
     expect(config).toMatchObject({
       stellarNetwork: 'testnet',
       stellarRpcUrl: 'https://soroban-testnet.stellar.org:443',
-      contractAddresses: [],
+      contractAddresses: [{ address: 'CTEST', events: ['*'] }],
       pollIntervalMs: 30000,
       maxReconnectAttempts: 5,
       reconnectDelayMs: 5000,
diff --git a/listener/src/config.ts b/listener/src/config.ts
index fe5c962..cea28cc 100644
--- a/listener/src/config.ts
+++ b/listener/src/config.ts
@@ -1,5 +1,4 @@
-import { Config, ContractConfig, DiscordConfig, WebhookSecret, AppCleanupConfig, EventQueueConfig, RetrySchedulerOptions } from './types';
-import { Config, ContractConfig, DiscordConfig, WebhookSecret, AppCleanupConfig, EventQueueConfig, RetrySchedulerOptions, AnalyticsConfig } from './types';
+import { Config, ContractConfig, DiscordConfig, WebhookSecret, ApiKey, AppCleanupConfig, EventQueueConfig, RetrySchedulerOptions, AnalyticsConfig } from './types';
 
 export class ConfigError extends Error {
   constructor(message: string) {
@@ -13,6 +12,22 @@ function trimEnv(name: string): string | undefined {
   return value === undefined ? undefined : value.trim();
 }
 
+// Environment variables the listener cannot safely start without.
+// Keep this list in sync with the "Required" column in
+// ENVIRONMENT_VARIABLES_AND_SECRETS.md.
+const REQUIRED_ENV_VARS = ['CONTRACT_ADDRESSES'];
+
+function validateRequiredEnvVars(): void {
+  const missing = REQUIRED_ENV_VARS.filter((name) => !trimEnv(name));
+
+  if (missing.length > 0) {
+    throw new ConfigError(
+      `Missing required environment variable(s): ${missing.join(', ')}. ` +
+        'Copy .env.example to .env and set them before starting the listener.'
+    );
+  }
+}
+
 function parseIntegerEnv(name: string, defaultValue: string): number {
   const rawValue = trimEnv(name);
   const value = rawValue !== undefined ? rawValue : defaultValue;
@@ -175,6 +190,8 @@ function loadRetrySchedulerConfig(): RetrySchedulerOptions {
 }
 
 export function loadConfig(): Config {
+  validateRequiredEnvVars();
+
   const discord = loadDiscordConfig();
   const rawContractAddresses = parseJsonEnv<unknown>('CONTRACT_ADDRESSES', '[]');
   const rawWebhookSecrets = parseJsonEnv<unknown>('WEBHOOK_SECRETS', '[]');
@@ -182,6 +199,7 @@ export function loadConfig(): Config {
     'RATE_LIMIT_CLIENT_OVERRIDES',
     '{}'
   );
+  const rawApiKeys = parseJsonEnv<unknown>('API_KEYS', '[]');
 
   return {
     stellarNetwork: trimEnv('STELLAR_NETWORK') || 'testnet',
diff --git a/listener/src/services/notification-retry-queue.ts b/listener/src/services/notification-retry-queue.ts
index a9fa5a9..3633fcd 100644
--- a/listener/src/services/notification-retry-queue.ts
+++ b/listener/src/services/notification-retry-queue.ts
@@ -68,15 +68,6 @@ export class NotificationRetryQueue {
     processingTimes: [] as number[],
   };
 
-  // Metrics
-  private metrics = {
-    totalEnqueued: 0,
-    totalProcessed: 0,
-    totalSucceeded: 0,
-    totalFailed: 0,
-    processingTimes: [] as number[],
-  };
-
   constructor(notificationFn: NotificationFn, options?: RetryQueueOptions) {
     this.notificationFn = notificationFn;
     this.baseDelayMs = options?.baseDelayMs ?? DEFAULTS.baseDelayMs;
@@ -120,9 +111,8 @@ export class NotificationRetryQueue {
     });
 
     this.queuedFingerprints.add(fingerprint);
-    this.queue.push({ event, contractConfig, retryCount: 0, nextRetryAt, requestId });
-    this.metrics.totalEnqueued++;
     this.queue.push({ event, contractConfig, retryCount: 0, nextRetryAt, requestId, priority, enqueuedAt: Date.now() });
+    this.metrics.totalEnqueued++;
   }
 
   start(): void {
diff --git a/listener/src/store/event-registry.ts b/listener/src/store/event-registry.ts
index 6d37485..fb3985f 100644
--- a/listener/src/store/event-registry.ts
+++ b/listener/src/store/event-registry.ts
@@ -29,10 +29,6 @@ export class EventRegistry {
     this.cleanupTimer = setInterval(() => this.pruneExpired(), intervalMs);
   }
 
-  setTtlMs(ms: number): void {
-    this.ttlMs = ms;
-  }
-
   stopCleanup(): void {
     if (this.cleanupTimer) {
       clearInterval(this.cleanupTimer);
@@ -119,3 +115,5 @@ export class EventRegistry {
 }
 
 export const eventRegistry = new EventRegistry();
+
+