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>

core/projects.py

@@ -44,6 +44,11 @@ STARTER_PROJECT_NAME = "My Workspace"
 
 @dataclass
 class Project:
+    """Một project: id, tên, mô tả, chỉ dẫn chung và thư mục sandbox.
+
+    Chỉ dẫn chung được chèn vào MỌI lượt chat thuộc project, nên đây là chỗ đặt
+    bối cảnh dùng lại thay vì gõ lại ở từng tin nhắn.
+    """
     project_id: str
     name: str
     description: str = ""
@@ -92,6 +97,7 @@ def ensure_starter_project(directory: Path = None) -> Project:
 
 
 def _slugify(name: str) -> str:
+    """Định danh an toàn cho tên file, suy từ tên project."""
     s = "".join(c if (c.isalnum() or c in "-_") else "-" for c in name.strip().lower())
     s = "-".join(filter(None, s.split("-")))
     return s or "project"
@@ -115,11 +121,14 @@ def new_project(name: str, description: str = "", instructions: str = "",
 
 
 def save_project(project: Project, directory: Path = None) -> Path:
+    """Ghi một project ra ``<project_id>.json`` (ghi nguyên tử)."""
     directory = directory or PROJECTS_DIR
-    directory.mkdir(parents=True, exist_ok=True)
     path = directory / f"{project.project_id}.json"
-    path.write_text(json.dumps(asdict(project), ensure_ascii=False, indent=2),
-                    encoding="utf-8")
+    # R06-T02: atomic write — a crash/kill between truncate and write used to
+    # leave a half-written project.json that load_project() then silently
+    # treats as "missing" (see infrastructure/persistence/json/atomic_write.py).
+    from ..infrastructure.persistence.json.atomic_write import write_json
+    write_json(path, asdict(project))
     return path