feat(daily-prep): persist last prep run to a log file and serve it via GetLastPrepLog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Worker/Hub/WorkerHub.cs

@@ -582,6 +582,19 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         await new DailyNoteRepository(ctx).DeleteAsync(id);
     }
 
+    public Task<string> GetLastPrepLog()
+    {
+        var path = DailyPrepPrompt.LogPath();
+        if (!File.Exists(path)) return Task.FromResult(string.Empty);
+
+        const int maxBytes = 256 * 1024;
+        var bytes = File.ReadAllBytes(path);
+        var text = bytes.Length <= maxBytes
+            ? System.Text.Encoding.UTF8.GetString(bytes)
+            : System.Text.Encoding.UTF8.GetString(bytes, bytes.Length - maxBytes, maxBytes);
+        return Task.FromResult(text);
+    }
+
     public async Task<int> ClearMyDay()
     {
         await using var ctx = await _dbFactory.CreateDbContextAsync();

src/ClaudeDo.Worker/Prime/DailyPrepPrompt.cs

@@ -5,6 +5,9 @@ public static class DailyPrepPrompt
     public const string CandidatesTool = "mcp__claudedo__get_daily_prep_candidates";
     public const string SetMyDayTool = "mcp__claudedo__set_my_day";
 
+    public static string LogPath() =>
+        System.IO.Path.Combine(ClaudeDo.Data.Paths.AppDataRoot(), "logs", "daily-prep.log");
+
     public static string BuildArgs(int maxTurns) =>
         "-p --output-format stream-json --verbose --permission-mode acceptEdits " +
         $"--max-turns {maxTurns} " +

src/ClaudeDo.Worker/Prime/PrimeRunner.cs

@@ -39,6 +39,10 @@ public sealed class PrimeRunner : IPrimeRunner
         var success = false;
         try
         {
+            var logPath = DailyPrepPrompt.LogPath();
+            try { if (File.Exists(logPath)) File.Delete(logPath); } catch { /* best effort */ }
+            await using var logWriter = new LogWriter(logPath);
+
             await _broadcaster.PrepStartedAsync();
 
             var cwd = Paths.AppDataRoot();
@@ -62,7 +66,11 @@ public sealed class PrimeRunner : IPrimeRunner
                 arguments: args,
                 prompt: prompt,
                 workingDirectory: cwd,
-                onStdoutLine: line => _broadcaster.PrepLineAsync(line),
+                onStdoutLine: async line =>
+                {
+                    await logWriter.WriteLineAsync(line);
+                    await _broadcaster.PrepLineAsync(line);
+                },
                 ct: timeoutCts.Token);
 
             success = result.IsSuccess;

tests/ClaudeDo.Worker.Tests/Prime/PrimeRunnerTests.cs

@@ -124,4 +124,27 @@ public class PrimeRunnerTests : IDisposable
         Assert.Single(broadcaster.FinishedResults);
         Assert.True(broadcaster.FinishedResults[0]);
     }
+
+    [Fact]
+    public async Task FireAsync_writes_last_run_to_prep_log_file()
+    {
+        var path = DailyPrepPrompt.LogPath();
+        if (File.Exists(path)) File.Delete(path);
+
+        var claude = new FakeClaudeProcess(emitLines: new[] { "lineA", "lineB" }, exitCode: 0, result: "ok");
+        var runner = NewRunner(claude, new RecordingPrimeBroadcaster());
+        await runner.FireAsync(new PrimeScheduleDto(Guid.Empty, 0, TimeSpan.Zero, true, null, null), CancellationToken.None);
+
+        var contents = await File.ReadAllTextAsync(path);
+        Assert.Contains("lineA", contents);
+        Assert.Contains("lineB", contents);
+
+        // Truncation: a second run with different lines replaces the file.
+        var claude2 = new FakeClaudeProcess(emitLines: new[] { "lineC" }, exitCode: 0, result: "ok");
+        var runner2 = NewRunner(claude2, new RecordingPrimeBroadcaster());
+        await runner2.FireAsync(new PrimeScheduleDto(Guid.Empty, 0, TimeSpan.Zero, true, null, null), CancellationToken.None);
+        var after = await File.ReadAllTextAsync(path);
+        Assert.DoesNotContain("lineA", after);
+        Assert.Contains("lineC", after);
+    }
 }