Feature/delta team/epic r04 (#7)

## Summary

epic r04 - begin refactor

## Change Type

- [x] Cowork feature
- [ ] Bug fix
- [ ] Core AI contribution
- [ ] Test / hardening
- [ ] Performance
- [ ] Documentation

## Related Work

Cowork Task:

Core Repo: http://34.143.229.138/gitea-admin/fsg-ai-core-assets

Core AI Issue:

Core Task:

Related PR:

## Scope

What is intentionally included?

What is intentionally NOT included?

## Validation

- [ ] Unit tests
- [ ] Integration tests
- [ ] Manual verification
- [ ] Regression check

Commands / evidence:

## Security Impact

Permission / credential / network / customer data impact:

## Compatibility

- [ ] No breaking change
- [ ] Breaking change documented

## Reviewer Notes

Anything Cowork reviewers should pay attention to.

---------

Co-authored-by: Anh Tran Nguyen Minh <anhtnm1@fpt.com>
Co-authored-by: Huong Le Thi Thien <huongltt35@fpt.com>
Co-authored-by: Nam Pham Dinh Thanh <nampdt@fpt.com>
Co-authored-by: Vu Dam Tuan <vudt15@fpt.com>
Co-authored-by: Hiep Ha Van <hiephv3@fpt.com>
Co-authored-by: Lam Hoang Van <lamhv7@fpt.com>
Reviewed-on: #7
Co-authored-by: Duy Le Huu <duylh19@fpt.com>

tests/fakes/fake_tool_executor.py

@@ -0,0 +1,71 @@
+"""Fake Tool Executor for isolated, offline agent tool-call verification.
+
+Allows tests to verify tool invocation arguments, mock tool return values,
+and simulate failures/delays without performing unsafe host disk or OS operations.
+"""
+from __future__ import annotations
+
+from typing import Any, Callable, Dict, List, Optional
+
+
+class FakeToolExecutor:
+    """Mock execution engine for agent tool-call dispatching."""
+
+    def __init__(self) -> None:
+        # History of all executed tool invocations: List of {"name": str, "args": dict, "result": dict}
+        self.call_log: List[Dict[str, Any]] = []
+        # Custom handlers registered per tool name
+        self.handlers: Dict[str, Callable[[Dict[str, Any]], Dict[str, Any]]] = {}
+        # Pre-programmed fixed responses keyed by tool name
+        self.mock_responses: Dict[str, Dict[str, Any]] = {}
+        # Default response when no specific handler or response is found
+        self.default_result: Dict[str, Any] = {"ok": True, "output": "Fake tool executed successfully."}
+
+    def register_handler(
+        self,
+        tool_name: str,
+        handler: Callable[[Dict[str, Any]], Dict[str, Any]],
+    ) -> FakeToolExecutor:
+        """Register a dynamic handler function for a specific tool name."""
+        self.handlers[tool_name] = handler
+        return self
+
+    def set_mock_response(
+        self,
+        tool_name: str,
+        result: Dict[str, Any],
+    ) -> FakeToolExecutor:
+        """Set a static return payload for a specific tool name."""
+        self.mock_responses[tool_name] = result
+        return self
+
+    def execute(self, tool_name: str, arguments: Dict[str, Any]) -> Dict[str, Any]:
+        """Execute a tool call using registered mocks and record invocation details."""
+        # 1. Resolve result from handler, preset response, or default fallback
+        if tool_name in self.handlers:
+            result = self.handlers[tool_name](arguments)
+        elif tool_name in self.mock_responses:
+            result = self.mock_responses[tool_name]
+        else:
+            result = dict(self.default_result)
+            result["tool"] = tool_name
+            result["received_args"] = arguments
+
+        # 2. Record execution trace for post-test assertions
+        self.call_log.append({
+            "name": tool_name,
+            "args": dict(arguments),
+            "result": dict(result),
+        })
+
+        return result
+
+    def get_calls_for(self, tool_name: str) -> List[Dict[str, Any]]:
+        """Retrieve all recorded calls for a given tool name."""
+        return [call for call in self.call_log if call["name"] == tool_name]
+
+    def reset(self) -> None:
+        """Clear recorded logs and registered mock responses."""
+        self.call_log.clear()
+        self.handlers.clear()
+        self.mock_responses.clear()