Add ConversationLog (start/append/end with monotonic per-convo index)

backend.tests/ConversationLogTests.cs

@@ -0,0 +1,71 @@
+using backend.Conversations;
+using backend.Data;
+using FluentAssertions;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace backend.tests;
+
+public class ConversationLogTests(ApiFactory factory) : IClassFixture<ApiFactory>
+{
+    private readonly ApiFactory _factory = factory;
+
+    private async Task<(AppDbContext db, ConversationLog log, Guid deviceId)> ArrangeAsync()
+    {
+        var scope = _factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+        var log = scope.ServiceProvider.GetRequiredService<ConversationLog>();
+        var deviceId = Guid.NewGuid();
+        return (db, log, deviceId);
+    }
+
+    [Fact]
+    public async Task Start_creates_conversation_row()
+    {
+        var (db, log, deviceId) = await ArrangeAsync();
+
+        var convo = await log.StartAsync(deviceId, default);
+
+        var row = await db.Conversations.FirstAsync(c => c.Id == convo.Id);
+        row.DeviceId.Should().Be(deviceId);
+        row.EndedAt.Should().BeNull();
+        row.EndReason.Should().Be(EndReason.Unknown);
+    }
+
+    [Fact]
+    public async Task Turns_are_persisted_with_monotonic_index_per_conversation()
+    {
+        var (db, log, deviceId) = await ArrangeAsync();
+        var convo = await log.StartAsync(deviceId, default);
+
+        await log.AppendUserAsync(convo.Id, "hi", default);
+        await log.AppendAssistantAsync(convo.Id, "hello there", default);
+        await log.AppendToolAsync(convo.Id, "get_current_time", "{}", "{\"now\":\"2026-06-11T00:00:00Z\"}", default);
+
+        var turns = await db.Turns
+            .Where(t => t.ConversationId == convo.Id)
+            .OrderBy(t => t.Index)
+            .ToListAsync();
+
+        turns.Should().HaveCount(3);
+        turns.Select(t => t.Index).Should().Equal(0, 1, 2);
+        turns.Select(t => t.Role).Should().Equal(TurnRole.User, TurnRole.Assistant, TurnRole.Tool);
+        turns[0].Text.Should().Be("hi");
+        turns[1].Text.Should().Be("hello there");
+        turns[2].ToolName.Should().Be("get_current_time");
+    }
+
+    [Fact]
+    public async Task End_sets_ended_at_and_reason()
+    {
+        var (db, log, deviceId) = await ArrangeAsync();
+        var convo = await log.StartAsync(deviceId, default);
+
+        await log.EndAsync(convo.Id, EndReason.Idle, default);
+
+        var row = await db.Conversations.FirstAsync(c => c.Id == convo.Id);
+        row.EndedAt.Should().NotBeNull();
+        row.EndReason.Should().Be(EndReason.Idle);
+    }
+}

backend/Conversations/ConversationLog.cs

@@ -0,0 +1,63 @@
+using backend.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace backend.Conversations;
+
+public class ConversationLog(AppDbContext db)
+{
+    public async Task<Conversation> StartAsync(Guid deviceId, CancellationToken ct)
+    {
+        var c = new Conversation
+        {
+            DeviceId = deviceId,
+            StartedAt = DateTimeOffset.UtcNow,
+        };
+        db.Conversations.Add(c);
+        await db.SaveChangesAsync(ct);
+        return c;
+    }
+
+    public Task AppendUserAsync(Guid conversationId, string text, CancellationToken ct)
+        => AppendAsync(conversationId, TurnRole.User, text: text, ct: ct);
+
+    public Task AppendAssistantAsync(Guid conversationId, string text, CancellationToken ct)
+        => AppendAsync(conversationId, TurnRole.Assistant, text: text, ct: ct);
+
+    public Task AppendToolAsync(
+        Guid conversationId, string toolName, string argsJson, string resultJson, CancellationToken ct)
+        => AppendAsync(conversationId, TurnRole.Tool,
+            toolName: toolName, argsJson: argsJson, resultJson: resultJson, ct: ct);
+
+    public async Task EndAsync(Guid conversationId, EndReason reason, CancellationToken ct)
+    {
+        var row = await db.Conversations.FirstAsync(c => c.Id == conversationId, ct);
+        row.EndedAt = DateTimeOffset.UtcNow;
+        row.EndReason = reason;
+        await db.SaveChangesAsync(ct);
+    }
+
+    private async Task AppendAsync(
+        Guid conversationId, TurnRole role,
+        string? text = null, string? toolName = null,
+        string? argsJson = null, string? resultJson = null,
+        CancellationToken ct = default)
+    {
+        var next = await db.Turns
+            .Where(t => t.ConversationId == conversationId)
+            .Select(t => (int?)t.Index)
+            .MaxAsync(ct) ?? -1;
+
+        db.Turns.Add(new Turn
+        {
+            ConversationId = conversationId,
+            Index = next + 1,
+            Role = role,
+            Text = text,
+            ToolName = toolName,
+            ToolArgsJson = argsJson,
+            ToolResultJson = resultJson,
+            CreatedAt = DateTimeOffset.UtcNow,
+        });
+        await db.SaveChangesAsync(ct);
+    }
+}

backend/Program.cs

@@ -33,6 +33,7 @@ builder.Services.AddAuthorization();
 builder.Services.AddScoped<backend.Devices.DeviceTokenService>();
 builder.Services.AddScoped<backend.Pairing.PairingService>();
 builder.Services.AddSingleton<backend.Install.InstallScriptBuilder>();
+builder.Services.AddScoped<backend.Conversations.ConversationLog>();
 
 var app = builder.Build();