Phase 4 tests: DatabaseService migrations + ContextSelectionService DB paths

17 tests against throwaway in-memory DatabaseService instances: all
v1-v8 tables/columns exist post-migration, settings CRUD, conversation
save/load round-trip, instance isolation between separate in-memory
queues, and ContextSelectionService's DB-coupled paths (starring,
excluded-range summaries, smartSelection end to end) that were
previously untestable.

oAITests/DatabaseServiceTests.swift

@@ -0,0 +1,123 @@
+//
+//  DatabaseServiceTests.swift
+//  oAITests
+//
+// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0
+// Copyright (C) 2026 Rune Olsen
+
+import Testing
+import Foundation
+@testable import oAI
+
+@Suite("DatabaseService migrations, against a throwaway in-memory queue")
+struct DatabaseServiceMigrationTests {
+
+    @Test("All v1-v8 tables exist after migration")
+    func allTablesExist() {
+        let db = DatabaseService.makeInMemory()
+        let expectedTables = [
+            "conversations", "messages", "settings", "command_history",
+            "email_logs", "message_metadata", "message_embeddings",
+            "conversation_embeddings", "conversation_summaries",
+        ]
+        for table in expectedTables {
+            #expect(db.tableExists(table), "expected table \(table) to exist")
+        }
+    }
+
+    @Test("v4 adds modelId to messages and primaryModel to conversations")
+    func v4AddsModelColumns() {
+        let db = DatabaseService.makeInMemory()
+        #expect(db.columnNames(in: "messages").contains("modelId"))
+        #expect(db.columnNames(in: "conversations").contains("primaryModel"))
+    }
+
+    @Test("messages table has the expected v1 columns")
+    func messagesTableColumns() {
+        let db = DatabaseService.makeInMemory()
+        let columns = Set(db.columnNames(in: "messages"))
+        let expected: Set<String> = ["id", "conversationId", "role", "content", "tokens", "cost", "timestamp", "sortOrder"]
+        #expect(expected.isSubset(of: columns))
+    }
+
+    @Test("message_metadata table has the expected v6 columns")
+    func messageMetadataColumns() {
+        let db = DatabaseService.makeInMemory()
+        let columns = Set(db.columnNames(in: "message_metadata"))
+        #expect(columns == ["message_id", "importance_score", "user_starred", "summary", "chunk_index"])
+    }
+
+    @Test("conversation_summaries table has the expected v8 columns")
+    func conversationSummariesColumns() {
+        let db = DatabaseService.makeInMemory()
+        let columns = Set(db.columnNames(in: "conversation_summaries"))
+        #expect(columns == ["id", "conversation_id", "start_message_index", "end_message_index", "summary", "token_count", "created_at", "summary_model"])
+    }
+
+    @Test("A nonexistent table reports as absent, not a crash")
+    func nonexistentTableReportsAbsent() {
+        let db = DatabaseService.makeInMemory()
+        #expect(db.tableExists("not_a_real_table") == false)
+    }
+
+    @Test("Two in-memory instances are isolated from each other")
+    func instancesAreIsolated() throws {
+        let dbA = DatabaseService.makeInMemory()
+        let dbB = DatabaseService.makeInMemory()
+
+        _ = try dbA.saveConversation(name: "only in A", messages: [Message(role: .user, content: "hi")])
+
+        #expect(try dbA.listConversations().count == 1)
+        #expect(try dbB.listConversations().count == 0)
+    }
+}
+
+@Suite("DatabaseService settings CRUD, against a throwaway in-memory queue")
+struct DatabaseServiceSettingsTests {
+
+    @Test("Round-trips a plain setting")
+    func roundTripsSetting() {
+        let db = DatabaseService.makeInMemory()
+        db.setSetting(key: "theme", value: "dark")
+        #expect((try? db.loadAllSettings()["theme"]) == "dark")
+    }
+
+    @Test("Deletes a setting")
+    func deletesSetting() {
+        let db = DatabaseService.makeInMemory()
+        db.setSetting(key: "temp", value: "1")
+        db.deleteSetting(key: "temp")
+        #expect((try? db.loadAllSettings()["temp"]) == nil)
+    }
+}
+
+@Suite("DatabaseService conversation + message persistence, against a throwaway in-memory queue")
+struct DatabaseServiceConversationTests {
+
+    @Test("Saving a conversation round-trips its messages via loadConversation")
+    func savesAndLoadsConversation() throws {
+        let db = DatabaseService.makeInMemory()
+        let messages = [
+            Message(role: .user, content: "hello"),
+            Message(role: .assistant, content: "hi there"),
+        ]
+        let saved = try db.saveConversation(name: "Test Chat", messages: messages)
+
+        let loaded = try db.loadConversation(id: saved.id)
+        #expect(loaded?.0.name == "Test Chat")
+        #expect(loaded?.1.map(\.content) == ["hello", "hi there"])
+    }
+
+    @Test("System messages are excluded from persistence")
+    func systemMessagesExcluded() throws {
+        let db = DatabaseService.makeInMemory()
+        let messages = [
+            Message(role: .system, content: "tool call"),
+            Message(role: .user, content: "hello"),
+        ]
+        let saved = try db.saveConversation(name: "Test", messages: messages)
+        let loaded = try db.loadConversation(id: saved.id)
+        #expect(loaded?.1.count == 1)
+        #expect(loaded?.1.first?.content == "hello")
+    }
+}