feat: harden Python workflow and structured planning

Replace the uv-specific skill with a portable Python skill and rewrite the default user system prompt as a concise, structured Markdown execution policy.

Normalize a single fenced structured-JSON response, retry invalid skill selection with think disabled, validate selected skill output, and make coding plans keep editing and verification in one task.

Document the file_edit patch payload, expose that contract in the tool catalog, and convert malformed patch input into a retryable tool failure instead of terminating the agent task.

Update configuration and runtime tests for the Python skill, exact tool catalog, structured-output retry, and implementation-and-verification planning guidance.

Verified with 82 Agent.Core tests and an agent-mcp Python scheduling scenario with 49 passing unittest cases.

1 files changed, 22 insertions, 6 deletions

diff --git a/src/Agent.Windows/Tools/WindowsToolBackend.cs b/src/Agent.Windows/Tools/WindowsToolBackend.cs
index c432894..5cbf853 100644
--- a/src/Agent.Windows/Tools/WindowsToolBackend.cs
+++ b/src/Agent.Windows/Tools/WindowsToolBackend.cs
@@ -97,6 +97,13 @@ public sealed class WindowsToolBackend(WindowsSandboxSettings settings, ISecurit
                 ErrorCode: ex.Code, ErrorCategory: ex.Category, TargetPath: ex.TargetPath,
                 RequiredPermission: ex.RequiredPermission, Resolution: ex.Resolution));
         }
+        catch (Exception ex) when (ex is ToolValidationException or JsonException or InvalidOperationException)
+        {
+            return Task.FromResult(new ToolExecutionResult(false, ex.Message, false,
+                $"{toolName}:tool.input_invalid:{ex.Message}", RetryAllowed: true,
+                ErrorCode: "tool.input_invalid", ErrorCategory: "tool",
+                Resolution: "Correct the Tool arguments using the published schema and retry."));
+        }
     }
 
     public async Task EndTaskAsync(Guid taskId, bool success, CancellationToken cancellationToken)
@@ -300,12 +307,21 @@ public sealed class WindowsToolBackend(WindowsSandboxSettings settings, ISecurit
     private static string ApplyPatch(string path, string patch)
     {
         string current = File.Exists(path) ? File.ReadAllText(path) : string.Empty;
-        using JsonDocument document = JsonDocument.Parse(patch);
-        string oldText = document.RootElement.GetProperty("old_text").GetString()!;
-        string newText = document.RootElement.GetProperty("new_text").GetString()!;
-        int first = current.IndexOf(oldText, StringComparison.Ordinal);
-        if (first < 0 || current.IndexOf(oldText, first + oldText.Length, StringComparison.Ordinal) >= 0) throw new InvalidOperationException("Patch old_text must match exactly once.");
-        return current[..first] + newText + current[(first + oldText.Length)..];
+        JsonDocument document;
+        try { document = JsonDocument.Parse(patch); }
+        catch (JsonException) { throw new ToolValidationException("Patch must be a JSON object string containing old_text and new_text; unified diff is unsupported."); }
+        using (document)
+        {
+            if (document.RootElement.ValueKind != JsonValueKind.Object ||
+                !document.RootElement.TryGetProperty("old_text", out JsonElement oldElement) || oldElement.ValueKind != JsonValueKind.String ||
+                !document.RootElement.TryGetProperty("new_text", out JsonElement newElement) || newElement.ValueKind != JsonValueKind.String)
+                throw new ToolValidationException("Patch must be a JSON object string containing string old_text and new_text fields.");
+            string oldText = oldElement.GetString()!;
+            string newText = newElement.GetString()!;
+            int first = current.IndexOf(oldText, StringComparison.Ordinal);
+            if (first < 0 || current.IndexOf(oldText, first + oldText.Length, StringComparison.Ordinal) >= 0) throw new InvalidOperationException("Patch old_text must match exactly once.");
+            return current[..first] + newText + current[(first + oldText.Length)..];
+        }
     }
 
     private sealed class TaskContext(TaskResourceJournal journal, TaskAclManager acl, Guid sessionId)