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

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

tests/ClaudeDo.Worker.Tests/Runner/RetryPromptTests.cs

@@ -0,0 +1,29 @@
+using ClaudeDo.Worker.Runner;
+
+namespace ClaudeDo.Worker.Tests.Runner;
+
+public class RetryPromptTests
+{
+    [Fact]
+    public void Generic_no_result_error_is_not_appended()
+    {
+        var prompt = TaskRunner.BuildRetryPrompt($"{ClaudeProcess.NoResultPrefix} 1 and no result.");
+        Assert.DoesNotContain("Captured error", prompt);
+        Assert.Contains("did not complete", prompt);
+    }
+
+    [Fact]
+    public void Real_error_is_appended()
+    {
+        var prompt = TaskRunner.BuildRetryPrompt("error CS1002: ; expected");
+        Assert.Contains("Captured error", prompt);
+        Assert.Contains("CS1002", prompt);
+    }
+
+    [Fact]
+    public void Null_error_yields_bare_prompt()
+    {
+        var prompt = TaskRunner.BuildRetryPrompt(null);
+        Assert.DoesNotContain("Captured error", prompt);
+    }
+}