add background body prefetch for recent messages (last 30 days)

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

Packages/MagnumOpusCore/Sources/SyncEngine/SyncCoordinator.swift

@@ -121,6 +121,8 @@ public final class SyncCoordinator {
 			emit(.newMessages(count: envelopes.count, mailbox: remoteMailbox.name))
 		}
 
+		await prefetchBodies(mailboxId: mailboxId)
+
 		try store.updateMailboxSync(
 			id: mailboxId,
 			uidValidity: status.uidValidity,
@@ -128,6 +130,26 @@ public final class SyncCoordinator {
 		)
 	}
 
+	/// Fetch full bodies for recent messages that don't have bodyText yet
+	private func prefetchBodies(mailboxId: String) async {
+		let thirtyDaysAgo = ISO8601DateFormatter().string(
+			from: Calendar.current.date(byAdding: .day, value: -30, to: Date())!
+		)
+		do {
+			let messages = try store.messages(mailboxId: mailboxId)
+			let recent = messages.filter { $0.bodyText == nil && $0.date >= thirtyDaysAgo }
+			for message in recent.prefix(50) {
+				guard !Task.isCancelled else { break }
+				let (text, html) = try await imapClient.fetchBody(uid: message.uid)
+				if text != nil || html != nil {
+					try store.storeBody(messageId: message.id, text: text, html: html)
+				}
+			}
+		} catch {
+			// Background prefetch failure is non-fatal
+		}
+	}
+
 	private func envelopeToRecord(
 		_ envelope: FetchedEnvelope, accountId: String, mailboxId: String
 	) -> MessageRecord {