filter thread list by selected mailbox, fix sidebar selection

- threadSummariesFromDB accepts optional mailboxId filter, uses EXISTS subquery
  to show only threads containing messages in the selected mailbox
- add selectMailbox() and selectPerspective() to MailViewModel for clean
  state transitions between folder view and GTD perspective view
- sidebar highlights selected mailbox/perspective, clears state on switch
- default to INBOX mailbox after first sync

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

Apps/MagnumOpus/ViewModels/MailViewModel.swift

@@ -168,12 +168,12 @@ final class MailViewModel {
 		}
 	}
 
-	func startObservingThreads(accountId: String) {
+	func startObservingThreads(accountId: String, mailboxId: String? = nil) {
 		guard let store else { return }
 		threadObservation?.cancel()
 		threadObservation = Task {
 			do {
-				for try await summaries in store.observeThreadSummaries(accountId: accountId) {
+				for try await summaries in store.observeThreadSummaries(accountId: accountId, mailboxId: mailboxId) {
 					self.threads = summaries
 				}
 			} catch {
@@ -184,6 +184,22 @@ final class MailViewModel {
 		}
 	}
 
+	func selectMailbox(_ mailbox: MailboxInfo) {
+		selectedMailbox = mailbox
+		selectedItem = nil
+		items = []
+		guard let accountConfig else { return }
+		startObservingThreads(accountId: accountConfig.id, mailboxId: mailbox.id)
+	}
+
+	func selectPerspective(_ perspective: Perspective) {
+		selectedMailbox = nil
+		selectedThread = nil
+		messages = []
+		loadPerspective(perspective)
+		loadAllPerspectiveCounts()
+	}
+
 	func selectThread(_ thread: ThreadSummary) {
 		selectedThread = thread
 		messageObservation?.cancel()
@@ -231,6 +247,10 @@ final class MailViewModel {
 			// Reload mailboxes after sync (they may have been created on first sync)
 			if let accountConfig {
 				await loadMailboxes(accountId: accountConfig.id)
+				// On first sync, default to INBOX view
+				if selectedMailbox == nil, let inbox = mailboxes.first(where: { $0.name.lowercased() == "inbox" }) {
+					selectMailbox(inbox)
+				}
 			}
 		} catch {
 			let desc = "\(error)"

Apps/MagnumOpus/Views/SidebarView.swift

@@ -9,26 +9,28 @@ struct SidebarView: View {
 			Section("Perspectives") {
 				ForEach(Perspective.allCases) { perspective in
 					Button {
-						viewModel.loadPerspective(perspective)
+						viewModel.selectPerspective(perspective)
 					} label: {
 						Label(perspective.label, systemImage: perspective.systemImage)
 							.badge(viewModel.perspectiveCounts[perspective] ?? 0)
 					}
 					.buttonStyle(.plain)
-					.listItemTint(viewModel.selectedPerspective == perspective ? .accentColor : nil)
+					.listItemTint(viewModel.selectedPerspective == perspective && viewModel.selectedMailbox == nil ? .accentColor : nil)
-					.fontWeight(viewModel.selectedPerspective == perspective ? .semibold : .regular)
+					.fontWeight(viewModel.selectedPerspective == perspective && viewModel.selectedMailbox == nil ? .semibold : .regular)
 				}
 			}
 
 			Section("Mailboxes") {
 				ForEach(viewModel.mailboxes) { mailbox in
 					Button {
-						viewModel.selectedMailbox = mailbox
+						viewModel.selectMailbox(mailbox)
 					} label: {
 						Label(mailbox.name, systemImage: mailbox.systemImage)
 							.badge(mailbox.unreadCount)
 					}
 					.buttonStyle(.plain)
+					.listItemTint(viewModel.selectedMailbox?.id == mailbox.id ? .accentColor : nil)
+					.fontWeight(viewModel.selectedMailbox?.id == mailbox.id ? .semibold : .regular)
 				}
 			}
 		}

Packages/MagnumOpusCore/Sources/MailStore/Queries.swift

@@ -16,16 +16,16 @@ extension MailStore {
 	}
 
 	/// Thread summaries with unread count and latest sender info, ordered by lastDate DESC
-	public func threadSummaries(accountId: String) throws -> [ThreadSummary] {
+	public func threadSummaries(accountId: String, mailboxId: String? = nil) throws -> [ThreadSummary] {
 		try dbWriter.read { db in
-			try Self.threadSummariesFromDB(db, accountId: accountId)
+			try Self.threadSummariesFromDB(db, accountId: accountId, mailboxId: mailboxId)
 		}
 	}
 
 	/// Observe thread summaries reactively — UI updates automatically on DB change.
-	public func observeThreadSummaries(accountId: String) -> AsyncValueObservation<[ThreadSummary]> {
+	public func observeThreadSummaries(accountId: String, mailboxId: String? = nil) -> AsyncValueObservation<[ThreadSummary]> {
 		ValueObservation.tracking { db -> [ThreadSummary] in
-			try Self.threadSummariesFromDB(db, accountId: accountId)
+			try Self.threadSummariesFromDB(db, accountId: accountId, mailboxId: mailboxId)
 		}.values(in: dbWriter)
 	}
 
@@ -44,7 +44,19 @@ extension MailStore {
 
 	// MARK: - Internal helpers
 
-	static func threadSummariesFromDB(_ db: Database, accountId: String) throws -> [ThreadSummary] {
+	static func threadSummariesFromDB(_ db: Database, accountId: String, mailboxId: String? = nil) throws -> [ThreadSummary] {
+		let mailboxFilter: String
+		let arguments: StatementArguments
+
+		if let mailboxId {
+			// Filter threads to only those containing messages in the specified mailbox
+			mailboxFilter = "AND EXISTS (SELECT 1 FROM threadMessage tm2 JOIN message m2 ON m2.id = tm2.messageId WHERE tm2.threadId = t.id AND m2.mailboxId = ?)"
+			arguments = [accountId, mailboxId]
+		} else {
+			mailboxFilter = ""
+			arguments = [accountId]
+		}
+
 		let sql = """
 			SELECT
 				t.id, t.accountId, t.subject, t.lastDate, t.messageCount,
@@ -53,10 +65,10 @@ extension MailStore {
 				(SELECT m.snippet FROM threadMessage tm JOIN message m ON m.id = tm.messageId WHERE tm.threadId = t.id ORDER BY m.date DESC LIMIT 1) as snippet,
 				(SELECT COUNT(*) FROM attachment a JOIN threadMessage tm ON tm.messageId = a.messageId WHERE tm.threadId = t.id) as attachmentCount
 			FROM thread t
-			WHERE t.accountId = ?
+			WHERE t.accountId = ? \(mailboxFilter)
 			ORDER BY t.lastDate DESC
 			"""
-		let rows = try Row.fetchAll(db, sql: sql, arguments: [accountId])
+		let rows = try Row.fetchAll(db, sql: sql, arguments: arguments)
 		return rows.map { row in
 			ThreadSummary(
 				id: row["id"],