fix(worker): surface the real reason a Claude run failed instead of a generic exit-code message

StreamAnalyzer now reads subtype/terminal_reason/errors from the CLI's result
event, and TaskRunner builds a specific ErrorMarkdown from them: max_turns names
the turn budget and points at set_task_config + requeue, api_error passes
through the provider's own message (which carries the reset time), and any
other terminal_reason is appended to the previous generic text instead of
staying invisible. Falls through to the old "exited with code N and no result"
text when there's no terminal_reason at all (a real crash).

src/ClaudeDo.Worker/Runner/TaskRunner.cs

@@ -352,6 +352,9 @@ public sealed class TaskRunner
                 },
                 ct);
 
+            if (!result.IsSuccess)
+                result = result with { ErrorMarkdown = BuildFailureMarkdown(result, config.MaxTurns) };
+
             // Update the run record with results. Use CancellationToken.None:
             // this is a terminal write that must always complete, even if the
             // caller's token is already cancelled.
@@ -597,6 +600,28 @@ public sealed class TaskRunner
         return string.Join("\n\n", trimmed);
     }
 
+    public static string? BuildFailureMarkdown(RunResult result, int? configuredMaxTurns)
+    {
+        switch (result.TerminalReason)
+        {
+            case "max_turns":
+                var ofConfigured = configuredMaxTurns is int m ? $" von {m}" : "";
+                return $"Turn-Budget erschöpft ({result.TurnCount}{ofConfigured} Turns). "
+                    + "Erhöhe `maxTurns` am Task (`set_task_config`) und stelle den Task erneut in die Queue "
+                    + "– der Worktree bleibt erhalten.";
+
+            case "api_error":
+                if (!string.IsNullOrWhiteSpace(result.ResultMarkdown)) return result.ResultMarkdown;
+                if (result.Errors.Count > 0) return string.Join(" ", result.Errors);
+                return result.ErrorMarkdown;
+
+            default:
+                return string.IsNullOrWhiteSpace(result.TerminalReason)
+                    ? result.ErrorMarkdown
+                    : $"{result.ErrorMarkdown} (terminal_reason: {result.TerminalReason})";
+        }
+    }
+
     public static string BuildRetryPrompt(string? capturedError)
     {
         var basePrompt = PromptFiles.ReadOrDefault(PromptKind.Retry);