feat: extract constants module (P2-10)

Centralises magic numbers and string literals into src/config/constants.ts
(FEED_MAX_BYTES, MAX_FEED_ITEMS, MAX_METADATA_EMAILS, ADMIN_COOKIE_MAX_AGE,
FORWARD_EMAIL_IPS_CACHE_TTL_MS, DEFAULT_LEASE_SECONDS, MAX_LEASE_SECONDS,
FEEDS_LIST_KEY). Consumers updated in storage.ts and feed-fetcher.ts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/config/constants.ts

@@ -0,0 +1,23 @@
+/** Maximum total size of emails stored per feed (bytes). */
+export const FEED_MAX_BYTES = 524288; // 512 KB
+
+/** Cache TTL for ForwardEmail.net IP list (milliseconds). */
+export const FORWARD_EMAIL_IPS_CACHE_TTL_MS = 24 * 60 * 60 * 1000; // 24 hours
+
+/** Admin session cookie max-age (seconds). */
+export const ADMIN_COOKIE_MAX_AGE = 60 * 60 * 24 * 7; // 1 week
+
+/** Maximum number of feed items exposed in RSS/Atom responses. */
+export const MAX_FEED_ITEMS = 20;
+
+/** Maximum number of email entries kept in feed metadata. */
+export const MAX_METADATA_EMAILS = 50;
+
+/** Default WebSub lease duration (seconds). */
+export const DEFAULT_LEASE_SECONDS = 86400; // 24 hours
+
+/** Maximum WebSub lease duration (seconds). */
+export const MAX_LEASE_SECONDS = 30 * 24 * 3600; // 30 days
+
+/** KV key for the global feed list. */
+export const FEEDS_LIST_KEY = "feeds:list";

src/utils/feed-fetcher.ts

@@ -1,6 +1,5 @@
 import { Env, FeedConfig, FeedMetadata, EmailData } from "../types";
-
-const MAX_FEED_ITEMS = 20;
+import { MAX_FEED_ITEMS } from "../config/constants";
 
 export interface FeedData {
   feedConfig: FeedConfig;

src/utils/storage.ts

@@ -5,6 +5,7 @@ import {
   FeedList,
   EmailMetadata,
 } from "../types";
+import { MAX_METADATA_EMAILS } from "../config/constants";
 
 /**
  * Store email data in KV
@@ -49,10 +50,13 @@ async function updateFeedMetadata(
   // Add new email to the beginning of the list
   metadata.emails.unshift(emailMetadata);
 
-  // Keep only the last 50 emails in the metadata; delete orphaned KV entries
-  const toDelete = metadata.emails.length > 50 ? metadata.emails.slice(50) : [];
+  // Keep only the last MAX_METADATA_EMAILS in the metadata; delete orphaned KV entries
+  const toDelete =
+    metadata.emails.length > MAX_METADATA_EMAILS
+      ? metadata.emails.slice(MAX_METADATA_EMAILS)
+      : [];
   if (toDelete.length > 0) {
-    metadata.emails = metadata.emails.slice(0, 50);
+    metadata.emails = metadata.emails.slice(0, MAX_METADATA_EMAILS);
   }
 
   await Promise.all([