feat(paths): PR6 T6.9 + T6.10 — workspace-scoped Paths

`Paths` learns a new top-level filesystem dimension. Precedence in
descending order:

- workspace_id given (PR6+):
  `{base_dir}/workspaces/{wid}/threads/{tid}/...`
  `{base_dir}/workspaces/{wid}/users/{uid}/memory.json`
  `{base_dir}/workspaces/{wid}/users/{uid}/agents/{name}/...`
- user_id only (legacy user-isolation): unchanged
- neither (very legacy): unchanged

API: every thread/sandbox/host/ACP helper now takes
`workspace_id: str | None = None` alongside the existing `user_id`,
plus `Paths.workspace_dir()` and `_validate_workspace_id()` for safe
id substitution. `resolve_virtual_path` likewise routes through the
new precedence. The migration script in T6.12 will walk the old
`users/{uid}/threads/...` tree and rewrite to the new shape.

15 new tests (workspace shape, validation, sandbox dirs, ACP,
user-memory/agents under workspace, traversal defence) pass; 46
existing path tests stay green.

backend/packages/harness/deerflow/config/paths.py

@@ -10,6 +10,7 @@ VIRTUAL_PATH_PREFIX = "/mnt/user-data"
 
 _SAFE_THREAD_ID_RE = re.compile(r"^[A-Za-z0-9_\-]+$")
 _SAFE_USER_ID_RE = re.compile(r"^[A-Za-z0-9_\-]+$")
+_SAFE_WORKSPACE_ID_RE = re.compile(r"^[A-Za-z0-9_\-]+$")
 
 
 def _default_local_base_dir() -> Path:
@@ -31,6 +32,13 @@ def _validate_user_id(user_id: str) -> str:
     return user_id
 
 
+def _validate_workspace_id(workspace_id: str) -> str:
+    """Validate a workspace ID before using it in filesystem paths."""
+    if not _SAFE_WORKSPACE_ID_RE.match(workspace_id):
+        raise ValueError(f"Invalid workspace_id {workspace_id!r}: only alphanumeric characters, hyphens, and underscores are allowed.")
+    return workspace_id
+
+
 def _join_host_path(base: str, *parts: str) -> str:
     """Join host filesystem path segments while preserving native style.
 
@@ -148,116 +156,129 @@ class Paths:
         """Legacy per-agent memory file: `{base_dir}/agents/{name}/memory.json`."""
         return self.agent_dir(name) / "memory.json"
 
-    def user_dir(self, user_id: str) -> Path:
-        """Directory for a specific user: `{base_dir}/users/{user_id}/`."""
+    def workspace_dir(self, workspace_id: str) -> Path:
+        """Directory for a specific workspace: `{base_dir}/workspaces/{workspace_id}/`.
+
+        PR6 introduces this as the top-level isolation dimension. Per-user
+        state and per-thread state both live underneath their workspace so
+        a user with access to two workspaces never sees state bleed between
+        them on the filesystem.
+        """
+        return self.base_dir / "workspaces" / _validate_workspace_id(workspace_id)
+
+    def user_dir(self, user_id: str, *, workspace_id: str | None = None) -> Path:
+        """Directory for a specific user.
+
+        When ``workspace_id`` is provided (PR6+):
+            ``{base_dir}/workspaces/{wid}/users/{user_id}/``
+
+        Otherwise (legacy layout):
+            ``{base_dir}/users/{user_id}/``
+        """
+        if workspace_id is not None:
+            return self.workspace_dir(workspace_id) / "users" / _validate_user_id(user_id)
         return self.base_dir / "users" / _validate_user_id(user_id)
 
-    def user_memory_file(self, user_id: str) -> Path:
-        """Per-user memory file: `{base_dir}/users/{user_id}/memory.json`."""
-        return self.user_dir(user_id) / "memory.json"
+    def user_memory_file(self, user_id: str, *, workspace_id: str | None = None) -> Path:
+        """Per-user memory file under the active workspace (legacy without)."""
+        return self.user_dir(user_id, workspace_id=workspace_id) / "memory.json"
 
-    def user_agents_dir(self, user_id: str) -> Path:
-        """Per-user root for that user's custom agents: `{base_dir}/users/{user_id}/agents/`."""
-        return self.user_dir(user_id) / "agents"
+    def user_agents_dir(self, user_id: str, *, workspace_id: str | None = None) -> Path:
+        """Per-user root for custom agents under the active workspace."""
+        return self.user_dir(user_id, workspace_id=workspace_id) / "agents"
 
-    def user_agent_dir(self, user_id: str, agent_name: str) -> Path:
-        """Per-user per-agent directory: `{base_dir}/users/{user_id}/agents/{name}/`."""
-        return self.user_agents_dir(user_id) / agent_name.lower()
+    def user_agent_dir(self, user_id: str, agent_name: str, *, workspace_id: str | None = None) -> Path:
+        """Per-user per-agent directory under the active workspace."""
+        return self.user_agents_dir(user_id, workspace_id=workspace_id) / agent_name.lower()
 
-    def user_agent_memory_file(self, user_id: str, agent_name: str) -> Path:
-        """Per-user per-agent memory: `{base_dir}/users/{user_id}/agents/{name}/memory.json`."""
-        return self.user_agent_dir(user_id, agent_name) / "memory.json"
+    def user_agent_memory_file(self, user_id: str, agent_name: str, *, workspace_id: str | None = None) -> Path:
+        """Per-user per-agent memory file under the active workspace."""
+        return self.user_agent_dir(user_id, agent_name, workspace_id=workspace_id) / "memory.json"
 
-    def thread_dir(self, thread_id: str, *, user_id: str | None = None) -> Path:
+    def thread_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> Path:
         """
         Host path for a thread's data.
 
-        When *user_id* is provided:
-            `{base_dir}/users/{user_id}/threads/{thread_id}/`
-        Otherwise (legacy layout):
-            `{base_dir}/threads/{thread_id}/`
+        Precedence — workspace beats user, both beat legacy:
 
-        This directory contains a `user-data/` subdirectory that is mounted
-        as `/mnt/user-data/` inside the sandbox.
+        * ``workspace_id`` given (PR6+):
+            ``{base_dir}/workspaces/{wid}/threads/{thread_id}/``
+        * ``user_id`` only (legacy after user-isolation migration):
+            ``{base_dir}/users/{user_id}/threads/{thread_id}/``
+        * neither (very legacy, pre-isolation):
+            ``{base_dir}/threads/{thread_id}/``
+
+        The contained ``user-data/`` subdirectory is mounted as
+        ``/mnt/user-data/`` inside the sandbox regardless of which form is
+        chosen — only the host-side parent differs.
 
         Raises:
-            ValueError: If `thread_id` or `user_id` contains unsafe characters (path
-                        separators or `..`) that could cause directory traversal.
+            ValueError: If any of the supplied ids contains unsafe characters.
         """
+        if workspace_id is not None:
+            return self.workspace_dir(workspace_id) / "threads" / _validate_thread_id(thread_id)
         if user_id is not None:
-            return self.user_dir(user_id) / "threads" / _validate_thread_id(thread_id)
+            return self.base_dir / "users" / _validate_user_id(user_id) / "threads" / _validate_thread_id(thread_id)
         return self.base_dir / "threads" / _validate_thread_id(thread_id)
 
-    def sandbox_work_dir(self, thread_id: str, *, user_id: str | None = None) -> Path:
+    def sandbox_work_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> Path:
         """
         Host path for the agent's workspace directory.
-        Host: `{base_dir}/threads/{thread_id}/user-data/workspace/`
-        Sandbox: `/mnt/user-data/workspace/`
+        Host: ``{thread_dir}/user-data/workspace/``
+        Sandbox: ``/mnt/user-data/workspace/``
         """
-        return self.thread_dir(thread_id, user_id=user_id) / "user-data" / "workspace"
+        return self.thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id) / "user-data" / "workspace"
 
-    def sandbox_uploads_dir(self, thread_id: str, *, user_id: str | None = None) -> Path:
-        """
-        Host path for user-uploaded files.
-        Host: `{base_dir}/threads/{thread_id}/user-data/uploads/`
-        Sandbox: `/mnt/user-data/uploads/`
-        """
-        return self.thread_dir(thread_id, user_id=user_id) / "user-data" / "uploads"
+    def sandbox_uploads_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> Path:
+        """Host path for user-uploaded files; sandbox: ``/mnt/user-data/uploads/``."""
+        return self.thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id) / "user-data" / "uploads"
 
-    def sandbox_outputs_dir(self, thread_id: str, *, user_id: str | None = None) -> Path:
-        """
-        Host path for agent-generated artifacts.
-        Host: `{base_dir}/threads/{thread_id}/user-data/outputs/`
-        Sandbox: `/mnt/user-data/outputs/`
-        """
-        return self.thread_dir(thread_id, user_id=user_id) / "user-data" / "outputs"
+    def sandbox_outputs_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> Path:
+        """Host path for agent-generated artifacts; sandbox: ``/mnt/user-data/outputs/``."""
+        return self.thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id) / "user-data" / "outputs"
 
-    def acp_workspace_dir(self, thread_id: str, *, user_id: str | None = None) -> Path:
+    def acp_workspace_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> Path:
         """
-        Host path for the ACP workspace of a specific thread.
-        Host: `{base_dir}/threads/{thread_id}/acp-workspace/`
-        Sandbox: `/mnt/acp-workspace/`
+        Host path for the ACP workspace of a specific thread; sandbox: ``/mnt/acp-workspace/``.
 
         Each thread gets its own isolated ACP workspace so that concurrent
         sessions cannot read each other's ACP agent outputs.
         """
-        return self.thread_dir(thread_id, user_id=user_id) / "acp-workspace"
+        return self.thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id) / "acp-workspace"
 
-    def sandbox_user_data_dir(self, thread_id: str, *, user_id: str | None = None) -> Path:
-        """
-        Host path for the user-data root.
-        Host: `{base_dir}/threads/{thread_id}/user-data/`
-        Sandbox: `/mnt/user-data/`
-        """
-        return self.thread_dir(thread_id, user_id=user_id) / "user-data"
+    def sandbox_user_data_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> Path:
+        """Host path for the user-data root; sandbox: ``/mnt/user-data/``."""
+        return self.thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id) / "user-data"
 
-    def host_thread_dir(self, thread_id: str, *, user_id: str | None = None) -> str:
+    def host_thread_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> str:
         """Host path for a thread directory, preserving Windows path syntax."""
+        if workspace_id is not None:
+            return _join_host_path(self._host_base_dir_str(), "workspaces", _validate_workspace_id(workspace_id), "threads", _validate_thread_id(thread_id))
         if user_id is not None:
             return _join_host_path(self._host_base_dir_str(), "users", _validate_user_id(user_id), "threads", _validate_thread_id(thread_id))
         return _join_host_path(self._host_base_dir_str(), "threads", _validate_thread_id(thread_id))
 
-    def host_sandbox_user_data_dir(self, thread_id: str, *, user_id: str | None = None) -> str:
+    def host_sandbox_user_data_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> str:
         """Host path for a thread's user-data root."""
-        return _join_host_path(self.host_thread_dir(thread_id, user_id=user_id), "user-data")
+        return _join_host_path(self.host_thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id), "user-data")
 
-    def host_sandbox_work_dir(self, thread_id: str, *, user_id: str | None = None) -> str:
+    def host_sandbox_work_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> str:
         """Host path for the workspace mount source."""
-        return _join_host_path(self.host_sandbox_user_data_dir(thread_id, user_id=user_id), "workspace")
+        return _join_host_path(self.host_sandbox_user_data_dir(thread_id, workspace_id=workspace_id, user_id=user_id), "workspace")
 
-    def host_sandbox_uploads_dir(self, thread_id: str, *, user_id: str | None = None) -> str:
+    def host_sandbox_uploads_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> str:
         """Host path for the uploads mount source."""
-        return _join_host_path(self.host_sandbox_user_data_dir(thread_id, user_id=user_id), "uploads")
+        return _join_host_path(self.host_sandbox_user_data_dir(thread_id, workspace_id=workspace_id, user_id=user_id), "uploads")
 
-    def host_sandbox_outputs_dir(self, thread_id: str, *, user_id: str | None = None) -> str:
+    def host_sandbox_outputs_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> str:
         """Host path for the outputs mount source."""
-        return _join_host_path(self.host_sandbox_user_data_dir(thread_id, user_id=user_id), "outputs")
+        return _join_host_path(self.host_sandbox_user_data_dir(thread_id, workspace_id=workspace_id, user_id=user_id), "outputs")
 
-    def host_acp_workspace_dir(self, thread_id: str, *, user_id: str | None = None) -> str:
+    def host_acp_workspace_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> str:
         """Host path for the ACP workspace mount source."""
-        return _join_host_path(self.host_thread_dir(thread_id, user_id=user_id), "acp-workspace")
+        return _join_host_path(self.host_thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id), "acp-workspace")
 
-    def ensure_thread_dirs(self, thread_id: str, *, user_id: str | None = None) -> None:
+    def ensure_thread_dirs(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> None:
         """Create all standard sandbox directories for a thread.
 
         Directories are created with mode 0o777 so that sandbox containers
@@ -271,24 +292,28 @@ class Paths:
         ACP agent invocation.
         """
         for d in [
-            self.sandbox_work_dir(thread_id, user_id=user_id),
-            self.sandbox_uploads_dir(thread_id, user_id=user_id),
-            self.sandbox_outputs_dir(thread_id, user_id=user_id),
-            self.acp_workspace_dir(thread_id, user_id=user_id),
+            self.sandbox_work_dir(thread_id, workspace_id=workspace_id, user_id=user_id),
+            self.sandbox_uploads_dir(thread_id, workspace_id=workspace_id, user_id=user_id),
+            self.sandbox_outputs_dir(thread_id, workspace_id=workspace_id, user_id=user_id),
+            self.acp_workspace_dir(thread_id, workspace_id=workspace_id, user_id=user_id),
         ]:
             d.mkdir(parents=True, exist_ok=True)
             d.chmod(0o777)
 
-    def delete_thread_dir(self, thread_id: str, *, user_id: str | None = None) -> None:
-        """Delete all persisted data for a thread.
-
-        The operation is idempotent: missing thread directories are ignored.
-        """
-        thread_dir = self.thread_dir(thread_id, user_id=user_id)
+    def delete_thread_dir(self, thread_id: str, *, workspace_id: str | None = None, user_id: str | None = None) -> None:
+        """Delete all persisted data for a thread. Idempotent."""
+        thread_dir = self.thread_dir(thread_id, workspace_id=workspace_id, user_id=user_id)
         if thread_dir.exists():
             shutil.rmtree(thread_dir)
 
-    def resolve_virtual_path(self, thread_id: str, virtual_path: str, *, user_id: str | None = None) -> Path:
+    def resolve_virtual_path(
+        self,
+        thread_id: str,
+        virtual_path: str,
+        *,
+        workspace_id: str | None = None,
+        user_id: str | None = None,
+    ) -> Path:
         """Resolve a sandbox virtual path to the actual host filesystem path.
 
         Args:
@@ -296,7 +321,8 @@ class Paths:
             virtual_path: Virtual path as seen inside the sandbox, e.g.
                           ``/mnt/user-data/outputs/report.pdf``.
                           Leading slashes are stripped before matching.
-            user_id: Optional user ID for user-scoped path resolution.
+            workspace_id: Optional workspace ID for workspace-scoped resolution.
+            user_id: Optional user ID for legacy user-scoped resolution.
 
         Returns:
             The resolved absolute host filesystem path.
@@ -314,7 +340,7 @@ class Paths:
             raise ValueError(f"Path must start with /{prefix}")
 
         relative = stripped[len(prefix) :].lstrip("/")
-        base = self.sandbox_user_data_dir(thread_id, user_id=user_id).resolve()
+        base = self.sandbox_user_data_dir(thread_id, workspace_id=workspace_id, user_id=user_id).resolve()
         actual = (base / relative).resolve()
 
         try:

backend/tests/test_paths_workspace.py

@@ -0,0 +1,115 @@
+"""PR6 T6.9 / T6.10 — workspace-scoped path resolution.
+
+The Paths class learns a new top-level dimension for multi-tenant
+filesystems: ``{base_dir}/workspaces/{wid}/...``. Precedence:
+
+- ``workspace_id`` given → new shape ``workspaces/{wid}/threads/{tid}/...``
+- only ``user_id`` given → legacy shape ``users/{uid}/threads/{tid}/...``
+- neither → very-legacy shape ``threads/{tid}/...``
+
+Per-user filesystem state (memory.json, custom agents) lives under the
+workspace too: ``workspaces/{wid}/users/{uid}/memory.json`` etc. — so a
+user's memory cannot be reused across workspaces by mistake.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from deerflow.config.paths import Paths
+
+
+@pytest.fixture
+def paths(tmp_path: Path) -> Paths:
+    return Paths(tmp_path)
+
+
+class TestValidateWorkspaceId:
+    def test_valid_workspace_id(self, paths: Paths):
+        d = paths.workspace_dir("ws-abc-123")
+        assert d == paths.base_dir / "workspaces" / "ws-abc-123"
+
+    def test_rejects_path_traversal(self, paths: Paths):
+        with pytest.raises(ValueError, match="Invalid workspace_id"):
+            paths.workspace_dir("../escape")
+
+    def test_rejects_slash(self, paths: Paths):
+        with pytest.raises(ValueError, match="Invalid workspace_id"):
+            paths.workspace_dir("ws/bar")
+
+    def test_rejects_empty(self, paths: Paths):
+        with pytest.raises(ValueError, match="Invalid workspace_id"):
+            paths.workspace_dir("")
+
+
+class TestWorkspaceScopedThreadDir:
+    def test_workspace_takes_precedence_over_user(self, paths: Paths):
+        """When both are given, workspace wins — user_id is recorded in the row, not the filesystem."""
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "threads" / "t1"
+        assert paths.thread_dir("t1", workspace_id="ws-alpha", user_id="alice") == expected
+
+    def test_workspace_only(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "threads" / "t1"
+        assert paths.thread_dir("t1", workspace_id="ws-alpha") == expected
+
+    def test_user_only_still_legacy(self, paths: Paths):
+        """Legacy callers keep the user_id-only shape until migration runs."""
+        expected = paths.base_dir / "users" / "alice" / "threads" / "t1"
+        assert paths.thread_dir("t1", user_id="alice") == expected
+
+    def test_no_ids_very_legacy(self, paths: Paths):
+        expected = paths.base_dir / "threads" / "t1"
+        assert paths.thread_dir("t1") == expected
+
+
+class TestEnsureThreadDirsWorkspace:
+    def test_creates_workspace_layout(self, paths: Paths):
+        paths.ensure_thread_dirs("t1", workspace_id="ws-alpha")
+        root = paths.base_dir / "workspaces" / "ws-alpha" / "threads" / "t1"
+        for sub in ("user-data/workspace", "user-data/uploads", "user-data/outputs", "acp-workspace"):
+            assert (root / sub).is_dir(), f"missing {sub}"
+
+
+class TestSandboxDirsWorkspace:
+    def test_sandbox_work_dir(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "threads" / "t1" / "user-data" / "workspace"
+        assert paths.sandbox_work_dir("t1", workspace_id="ws-alpha") == expected
+
+    def test_sandbox_uploads_dir(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "threads" / "t1" / "user-data" / "uploads"
+        assert paths.sandbox_uploads_dir("t1", workspace_id="ws-alpha") == expected
+
+    def test_sandbox_outputs_dir(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "threads" / "t1" / "user-data" / "outputs"
+        assert paths.sandbox_outputs_dir("t1", workspace_id="ws-alpha") == expected
+
+
+class TestUserMemoryUnderWorkspace:
+    def test_user_memory_file_under_workspace(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "users" / "alice" / "memory.json"
+        assert paths.user_memory_file("alice", workspace_id="ws-alpha") == expected
+
+    def test_user_memory_file_legacy_without_workspace(self, paths: Paths):
+        expected = paths.base_dir / "users" / "alice" / "memory.json"
+        assert paths.user_memory_file("alice") == expected
+
+    def test_user_agents_dir_under_workspace(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "users" / "alice" / "agents"
+        assert paths.user_agents_dir("alice", workspace_id="ws-alpha") == expected
+
+    def test_user_agent_memory_file_under_workspace(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "users" / "alice" / "agents" / "code-reviewer" / "memory.json"
+        assert paths.user_agent_memory_file("alice", "code-reviewer", workspace_id="ws-alpha") == expected
+
+
+class TestVirtualPathResolutionWorkspace:
+    def test_resolve_virtual_path_workspace_scope(self, paths: Paths):
+        expected = paths.base_dir / "workspaces" / "ws-alpha" / "threads" / "t1" / "user-data" / "outputs" / "x.json"
+        actual = paths.resolve_virtual_path("t1", "/mnt/user-data/outputs/x.json", workspace_id="ws-alpha")
+        assert actual == expected.resolve()
+
+    def test_resolve_virtual_path_rejects_traversal_under_workspace(self, paths: Paths):
+        with pytest.raises(ValueError, match="path traversal"):
+            paths.resolve_virtual_path("t1", "/mnt/user-data/../../etc/passwd", workspace_id="ws-alpha")