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>

src/ClaudeDo.Worker/External/NotesMcpTools.cs

@@ -0,0 +1,59 @@
+using System.ComponentModel;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Hub;
+using ModelContextProtocol.Server;
+
+namespace ClaudeDo.Worker.External;
+
+public sealed record AddNoteResult(bool Saved, string Id, int AgentNotesToday, int RemainingToday);
+
+[McpServerToolType]
+public sealed class NotesMcpTools
+{
+    /// <summary>Agent-written notes allowed per day. The user's own notes are never counted or
+    /// capped — this only stops an agent from burying the day in its own bullets.</summary>
+    public const int DailyAgentCap = 10;
+
+    /// <summary>A note is a line, not a report. Longer output belongs in a task or a finding.</summary>
+    public const int MaxLength = 500;
+
+    private readonly DailyNoteRepository _notes;
+    private readonly HubBroadcaster _broadcaster;
+
+    public NotesMcpTools(DailyNoteRepository notes, HubBroadcaster broadcaster)
+    {
+        _notes = notes;
+        _broadcaster = broadcaster;
+    }
+
+    [McpServerTool, Description(
+        "Add one short line to the user's notes for today — the day log they read in ClaudeDo, " +
+        "not a log for you. Write only what the user would want to reread later and would " +
+        "otherwise lose: a decision they made, something you found that changes their plans, " +
+        "something they asked you to remember for the day. Task status, your progress and " +
+        "anything already visible in the task list are noise here. When unsure, don't. " +
+        "Capped at 10 agent notes per day; you cannot edit or delete notes, so a bad one stays " +
+        "until the user removes it.")]
+    public async Task<AddNoteResult> AddNote(
+        [Description("The note itself: one plain sentence, no markdown, no prefix, max 500 characters.")] string text,
+        CancellationToken cancellationToken = default)
+    {
+        var trimmed = (text ?? "").Trim();
+        if (trimmed.Length == 0)
+            throw new InvalidOperationException("text is required.");
+        if (trimmed.Length > MaxLength)
+            throw new InvalidOperationException(
+                $"Note is {trimmed.Length} characters, the limit is {MaxLength}. Shorten it to one line.");
+
+        var today = DateOnly.FromDateTime(DateTime.Today);
+        var used = await _notes.CountAgentNotesAsync(today, cancellationToken);
+        if (used >= DailyAgentCap)
+            throw new InvalidOperationException(
+                $"Daily cap reached: {DailyAgentCap} agent notes already written today. " +
+                "Nothing was saved — tell the user instead of retrying.");
+
+        var note = await _notes.AddAsync(today, trimmed, fromAgent: true, cancellationToken);
+        await _broadcaster.NotesUpdated();
+        return new AddNoteResult(true, note.Id, used + 1, DailyAgentCap - used - 1);
+    }
+}