feat(prompts): retry prompt from file, append only real captured errors

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

src/ClaudeDo.Worker/Runner/ClaudeProcess.cs

@@ -6,6 +6,8 @@ namespace ClaudeDo.Worker.Runner;
 
 public sealed class ClaudeProcess : IClaudeProcess
 {
+    public const string NoResultPrefix = "Claude exited with code";
+
     private readonly WorkerConfig _cfg;
     private readonly ILogger<ClaudeProcess> _logger;
 
@@ -100,7 +102,7 @@ public sealed class ClaudeProcess : IClaudeProcess
 
         var error = lastStderr.Length > 0
             ? lastStderr.ToString().Trim()
-            : $"Claude exited with code {exitCode} and no result.";
+            : $"{NoResultPrefix} {exitCode} and no result.";
 
         return new RunResult
         {

src/ClaudeDo.Worker/Runner/TaskRunner.cs

@@ -104,7 +104,7 @@ public sealed class TaskRunner
                 {
                     _logger.LogInformation("Auto-retrying task {TaskId} with session {SessionId}", task.Id, result.SessionId);
                     var retryConfig = resolvedConfig with { ResumeSessionId = result.SessionId };
-                    var retryPrompt = $"The previous attempt failed with:\n\n{result.ErrorMarkdown}\n\nTry again and fix the issues.";
+                    var retryPrompt = BuildRetryPrompt(result.ErrorMarkdown);
 
                     var retryResult = await RunOnceAsync(task.Id, task.Title, slot, runDir, retryConfig, 2, true, retryPrompt, ct);
 
@@ -403,4 +403,14 @@ public sealed class TaskRunner
             .Select(p => p!.Trim());
         return string.Join("\n\n", trimmed);
     }
+
+    public static string BuildRetryPrompt(string? capturedError)
+    {
+        var basePrompt = PromptFiles.ReadOrDefault(PromptKind.Retry);
+        var isReal = !string.IsNullOrWhiteSpace(capturedError)
+            && !capturedError!.StartsWith(ClaudeProcess.NoResultPrefix, StringComparison.Ordinal);
+        return isReal
+            ? $"{basePrompt}\n\nCaptured error from the failed run:\n\n{capturedError!.Trim()}"
+            : basePrompt;
+    }
 }