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, 0 deletions

diff --git a/src/Agent.Core/Runtime/StructuredJson.cs b/src/Agent.Core/Runtime/StructuredJson.cs
new file mode 100644
index 0000000..e0c1650
--- /dev/null
+++ b/src/Agent.Core/Runtime/StructuredJson.cs
@@ -0,0 +1,22 @@
+namespace Agent.Core.Runtime;
+
+internal static class StructuredJson
+{
+    public static string Unwrap(string content)
+    {
+        string value = content.Trim();
+        int fenceStart = value.IndexOf("```", StringComparison.Ordinal);
+        if (fenceStart < 0) return value;
+        int firstLineEnd = value.IndexOf('\n', fenceStart);
+        if (firstLineEnd < 0) return value;
+        string opening = value[fenceStart..firstLineEnd].TrimEnd('\r');
+        if (!string.Equals(opening, "```", StringComparison.Ordinal) &&
+            !string.Equals(opening, "```json", StringComparison.OrdinalIgnoreCase))
+            return value;
+
+        int fenceEnd = value.IndexOf("```", firstLineEnd + 1, StringComparison.Ordinal);
+        if (fenceEnd < 0 || value.IndexOf("```", fenceEnd + 3, StringComparison.Ordinal) >= 0)
+            return value;
+        return value[(firstLineEnd + 1)..fenceEnd].Trim();
+    }
+}