feat(notes): add_note MCP tool with a per-day agent cap

Agents can write into the user's daily notes, but only within limits:
max 10 agent notes a day, max 500 characters, add only — no edit, no
delete. A new from_agent column separates their lines from the user's
so the cap counts the right ones and the UI can mark them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/ClaudeDo.Worker.Tests/External/NotesMcpToolsTests.cs

@@ -0,0 +1,77 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.External;
+using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Tests.Infrastructure;
+
+namespace ClaudeDo.Worker.Tests.External;
+
+public sealed class NotesMcpToolsTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly ClaudeDoDbContext _ctx;
+    private readonly DailyNoteRepository _notes;
+    private readonly NotesMcpTools _sut;
+    private static readonly DateOnly Today = DateOnly.FromDateTime(DateTime.Today);
+
+    public NotesMcpToolsTests()
+    {
+        _ctx = _db.CreateContext();
+        _notes = new DailyNoteRepository(_ctx);
+        _sut = new NotesMcpTools(_notes, new HubBroadcaster(new CapturingHubContext()));
+    }
+
+    public void Dispose() { _ctx.Dispose(); _db.Dispose(); }
+
+    [Fact]
+    public async Task AddNote_stores_it_on_today_flagged_as_agent_written()
+    {
+        var result = await _sut.AddNote("  Mika decided to keep the daily grouping.  ");
+
+        Assert.True(result.Saved);
+        var row = Assert.Single(await _notes.ListByDayAsync(Today));
+        Assert.Equal("Mika decided to keep the daily grouping.", row.Text);
+        Assert.True(row.FromAgent);
+        Assert.Equal(NotesMcpTools.DailyAgentCap - 1, result.RemainingToday);
+    }
+
+    [Fact]
+    public async Task AddNote_refuses_once_the_daily_cap_is_used_up_and_saves_nothing()
+    {
+        for (var i = 0; i < NotesMcpTools.DailyAgentCap; i++)
+            await _sut.AddNote($"note {i}");
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => _sut.AddNote("one too many"));
+
+        Assert.Contains("cap", ex.Message, StringComparison.OrdinalIgnoreCase);
+        Assert.Equal(NotesMcpTools.DailyAgentCap, (await _notes.ListByDayAsync(Today)).Count);
+    }
+
+    [Fact]
+    public async Task Notes_the_user_wrote_do_not_count_against_the_agent_cap()
+    {
+        for (var i = 0; i < NotesMcpTools.DailyAgentCap; i++)
+            await _notes.AddAsync(Today, $"mine {i}");
+
+        var result = await _sut.AddNote("still allowed");
+
+        Assert.Equal(1, result.AgentNotesToday);
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    public async Task AddNote_rejects_empty_text(string text) =>
+        await Assert.ThrowsAsync<InvalidOperationException>(() => _sut.AddNote(text));
+
+    [Fact]
+    public async Task AddNote_rejects_text_past_the_length_limit()
+    {
+        var tooLong = new string('x', NotesMcpTools.MaxLength + 1);
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => _sut.AddNote(tooLong));
+
+        Assert.Contains(NotesMcpTools.MaxLength.ToString(), ex.Message);
+        Assert.Empty(await _notes.ListByDayAsync(Today));
+    }
+}