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>

domain/workspaces/workspace_session.py

@@ -0,0 +1,99 @@
+"""WorkspaceSession - an immutable snapshot of which project a turn belongs
+to and where it may touch the filesystem (R06-T01).
+
+``state.py::AppContext.active_project_id`` is a single mutable field read by
+every background worker thread. ``ui/workspace_tab.py::_load_current`` writes
+it (and the related ``config._project_history_dir``) on the UI thread the
+moment the user switches projects - while a turn already running on a
+worker thread may read either field mid-switch and end up acting on the
+OTHER project's workspace/history for the rest of its run (the race
+R06-T04 fixes).
+
+The fix, same shape as R04's ``ConversationExecutionRequest``: capture the
+workspace facts a turn needs ONCE, on the thread that knows which project is
+selected, into one frozen object. Whatever the user does to the UI afterwards,
+the turn keeps using the workspace it was handed at submit time.
+
+Pure domain code: stdlib only, no Qt, no network. It does touch ``Path`` (not
+plain strings, unlike ``ConversationExecutionRequest``) because its whole job
+is path-containment checking - a snapshot with no room to answer "is this
+path mine" would not replace what ``ToolContext.resolve`` currently does
+inline.
+"""
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Tuple
+
+
+@dataclass(frozen=True)
+class WorkspaceSession:
+    """Everything a turn needs to know about ITS workspace, fixed at the
+    moment it was submitted.
+
+    Attributes:
+        project_id: the project this turn belongs to (``""`` when no project
+            is selected - e.g. the Code tab, which has no project concept).
+        workspace_root: the project's sandbox root (``Project.workspace_dir()``).
+        sandbox_dir: the ``.scratch`` subtree inside ``workspace_root`` used for
+            generator/helper scripts, never a final deliverable (see
+            ``infrastructure/filesystem/file_tools.py::_flatten_rel``).
+        allowed_paths: every root a tool call may read/write under. Almost
+            always just ``(workspace_root,)``; a project with a custom
+            ``output_dir`` outside the managed workspace tree still resolves
+            to exactly one root - the tuple exists so a future caller (e.g. a
+            step scoped to a shared input folder) can widen it without a
+            shape change.
+    """
+
+    project_id: str
+    workspace_root: Path
+    sandbox_dir: Path
+    allowed_paths: Tuple[Path, ...] = field(default_factory=tuple)
+
+    def __post_init__(self) -> None:
+        """Không khai đường dẫn cho phép thì mặc định đúng một đường: thư mục gốc của
+        phiên. Để rỗng nghĩa là KHÔNG cho phép gì cả, không phải cho phép tất.
+        """
+        if not self.allowed_paths:
+            object.__setattr__(self, "allowed_paths", (self.workspace_root,))
+
+    @classmethod
+    def from_project(cls, project) -> "WorkspaceSession":
+        """Build a session from a ``core.projects.Project``. ``project`` is
+        typed loosely (not imported) so this module has no dependency on
+        ``core/`` - the caller (``core/projects.py`` itself, or
+        ``application/conversations``) already has the Project in hand."""
+        root = Path(project.workspace_dir())
+        return cls(project_id=project.project_id, workspace_root=root,
+                   sandbox_dir=root / ".scratch", allowed_paths=(root,))
+
+    @classmethod
+    def unscoped(cls, workspace_root: Path) -> "WorkspaceSession":
+        """A session for callers with no project concept (e.g. the Code tab,
+        which sandboxes to a plain folder rather than a ``Project``)."""
+        root = Path(workspace_root)
+        return cls(project_id="", workspace_root=root, sandbox_dir=root / ".scratch")
+
+    def is_allowed(self, path: Path) -> bool:
+        """True when ``path`` resolves inside one of :attr:`allowed_paths`.
+
+        Same containment rule as ``ToolContext.resolve`` (an exact root match
+        or a real descendant), but side-effect-free: it reports the answer
+        instead of raising, so a caller (``FileWorkspaceService``, R06-T05)
+        can decide what "not allowed" means for its own UI instead of
+        catching a ``ToolError``.
+        """
+        try:
+            resolved = Path(path).expanduser().resolve()
+        except OSError:
+            return False
+        for allowed in self.allowed_paths:
+            root = Path(allowed).resolve()
+            if resolved == root or root in resolved.parents:
+                return True
+        return False
+
+
+__all__ = ["WorkspaceSession"]