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.

2 files changed, 15 insertions, 4 deletions

diff --git a/tests/Agent.Core.Tests/ConfigurationTests.cs b/tests/Agent.Core.Tests/ConfigurationTests.cs
index f6db9f2..64b2d85 100644
--- a/tests/Agent.Core.Tests/ConfigurationTests.cs
+++ b/tests/Agent.Core.Tests/ConfigurationTests.cs
@@ -139,14 +139,14 @@ public sealed class ConfigurationTests
         // Legacy single markdown — should be ignored (not loaded).
         directory.File("skills/legacy.md", "legacy skill");
         // Standard skill directory with frontmatter.
-        directory.File("skills/python-via-uv/SKILL.md", "---\nname: python-via-uv\ndescription: Python execution skill.\n---\n# Python via uv\nInstructions here.");
+        directory.File("skills/python/SKILL.md", "---\nname: python\ndescription: Python execution skill.\n---\n# Python\nInstructions here.");
         // Non-SKILL.md files in skill directory should not be loaded as skills.
-        directory.File("skills/python-via-uv/reference.md", "must not be loaded as a skill");
+        directory.File("skills/python/reference.md", "must not be loaded as a skill");
 
         var skills = SkillLoader.Load(Path.Combine(directory.Path, "skills"));
 
         Assert.Single(skills);
-        Assert.Equal("python-via-uv", skills[0].Name);
+        Assert.Equal("python", skills[0].Name);
         Assert.Equal("Python execution skill.", skills[0].Description);
         Assert.Contains("Instructions here.", skills[0].Instructions);
     }
diff --git a/tests/Agent.Core.Tests/PromptAndRuntimeTests.cs b/tests/Agent.Core.Tests/PromptAndRuntimeTests.cs
index fef5340..6dad528 100644
--- a/tests/Agent.Core.Tests/PromptAndRuntimeTests.cs
+++ b/tests/Agent.Core.Tests/PromptAndRuntimeTests.cs
@@ -284,6 +284,10 @@ public sealed class PromptAndRuntimeTests
         Assert.Equal(AgentTaskState.Completed, completed!.State);
         Assert.Equal([null, false], ollama.ThinkOverrides);
         Assert.All(ollama.Temperatures, value => Assert.Equal(0.7, value));
+        Assert.Contains(ollama.PlanningMessages[0], message =>
+            message.Role == "system" && message.Content.Contains("There is no file_write Tool", StringComparison.Ordinal));
+        Assert.Contains(ollama.PlanningMessages[0], message =>
+            message.Role == "system" && message.Content.Contains("one implementation-and-verification Task", StringComparison.Ordinal));
         Assert.Contains(ollama.PlanningMessages[1], message =>
             message.Role == "system" && message.Content.Contains("Do not call or execute any Tool", StringComparison.Ordinal));
     }
@@ -615,7 +619,14 @@ public sealed class PromptAndRuntimeTests
             Temperatures.Add(temperatureOverride);
             PlanningMessages.Add(messages);
             string content = ThinkOverrides.Count == 2 && succeedOnRetry
-                ? """{"tasks":[{"description":"analyze","dependencies":[],"budget_class":"4K","optimistic_tokens":10,"most_likely_tokens":20,"pessimistic_tokens":30,"requires_external_effect":false}]}"""
+                ? """
+                  Here is the requested plan.
+
+                  ```json
+                  {"tasks":[{"description":"analyze","dependencies":[],"budget_class":"4K","optimistic_tokens":10,"most_likely_tokens":20,"pessimistic_tokens":30,"requires_external_effect":false}]}
+                  ```
+                  The JSON above is the complete plan.
+                  """
                 : "not-json";
             return Task.FromResult(new OllamaResult(content, 1, 1));
         }