Perform a one-time (per local account) cleanup made necessary by the retention policy change — mark articles older than the 90-day window as read. This way users won’t get a flood of old, unread articles when they run this new version.

Frameworks/Account/Account.swift

@@ -279,7 +279,19 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
 		webFeedMetadataFile.load()
 		opmlFile.load()
 
+		var shouldHandleRetentionPolicyChange = false
+		if type == .onMyMac {
+			let didHandlePolicyChange = metadata.performedApril2020RetentionPolicyChange ?? false
+			shouldHandleRetentionPolicyChange = !didHandlePolicyChange
+		}
+
 		DispatchQueue.main.async {
+			if shouldHandleRetentionPolicyChange {
+				// Handle one-time database changes made necessary by April 2020 retention policy change.
+				self.database.performApril2020RetentionPolicyChange()
+				self.metadata.performedApril2020RetentionPolicyChange = true
+			}
+
 			self.database.cleanupDatabaseAtStartup(subscribedToWebFeedIDs: self.flattenedWebFeeds().webFeedIDs())
 			self.fetchAllUnreadCounts()
 		}

Frameworks/Account/AccountMetadata.swift

@@ -24,6 +24,7 @@ final class AccountMetadata: Codable {
 		case lastArticleFetchEndTime
 		case endpointURL
 		case lastCredentialRenewTime = "lastCredentialRenewTime"
+		case performedApril2020RetentionPolicyChange
 	}
 
 	var name: String? {
@@ -92,6 +93,14 @@ final class AccountMetadata: Codable {
 		}
 	}
 
+	var performedApril2020RetentionPolicyChange: Bool? {
+		didSet {
+			if performedApril2020RetentionPolicyChange != oldValue {
+				valueDidChange(.performedApril2020RetentionPolicyChange)
+			}
+		}
+	}
+
 	weak var delegate: AccountMetadataDelegate?
 	
 	func valueDidChange(_ key: CodingKeys) {

Frameworks/ArticlesDatabase/ArticlesDatabase.swift

@@ -277,6 +277,24 @@ public final class ArticlesDatabase {
 		articlesTable.deleteArticlesNotInSubscribedToFeedIDs(subscribedToWebFeedIDs)
 		articlesTable.deleteOldStatuses()
 	}
+
+	/// Do database cleanups made necessary by the retention policy change in April 2020.
+	///
+	/// The retention policy for feed-based systems changed in April 2020:
+	/// we keep articles only for as long as they’re in the feed.
+	/// This change could result in a bunch of older articles suddenly
+	/// appearing as unread articles.
+	///
+	/// These are articles that were in the database,
+	/// but weren’t appearing in the UI because they were beyond the 90-day window.
+	/// (The previous retention policy used a 90-day window.)
+	///
+	/// This function marks everything as read that’s beyond that 90-day window.
+	/// It’s intended to be called only once on an account.
+	public func performApril2020RetentionPolicyChange() {
+		precondition(retentionStyle == .feedBased)
+		articlesTable.markOlderStatusesAsRead()
+	}
 }
 
 // MARK: - Private

Frameworks/ArticlesDatabase/ArticlesTable.swift

@@ -580,6 +580,22 @@ final class ArticlesTable: DatabaseTable {
 			}
 		}
 	}
+
+	/// Mark statuses beyond the 90-day window as read.
+	///
+	/// This is not intended for wide use: this is part of implementing
+	/// the April 2020 retention policy change for feed-based accounts.
+	func markOlderStatusesAsRead() {
+		queue.runInDatabase { databaseResult in
+			guard let database = databaseResult.database else {
+				return
+			}
+
+			let sql = "update statuses set read = true where dateArrived<?;"
+			let parameters = [self.articleCutoffDate] as [Any]
+			database.executeUpdate(sql, withArgumentsIn: parameters)
+		}
+	}
 }
 
 // MARK: - Private