diff --git a/CHANGELOG.md b/CHANGELOG.md
index 63881901b..c5e2cdea9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -548,6 +548,16 @@ This section accumulates work toward the **2.1.0** milestone
 
 ### Fixed
 
+- **artifacts:** Keep `PUT /api/threads/{id}/artifacts/{path}` confined to
+  `/mnt/user-data/outputs`. The outputs-only guard was a string-prefix check on
+  the raw path, so a percent-encoded `..` (`outputs/%2e%2e/uploads/x.txt`) —
+  which nginx forwards untouched and Starlette decodes — passed it, and the
+  resolver only confines to `user-data/`, letting a caller overwrite a sibling
+  upload or workspace file in their own thread. Dot segments are now collapsed
+  before the prefix check, and the resolved host path is re-checked against the
+  resolved outputs root so a symlink planted inside `outputs/` cannot redirect
+  the write either. The rule now lives in one shared helper that IM-channel
+  attachment delivery uses as well, so the two copies cannot drift. ([#5321])
 - **gateway:** Stop persisting a caller-supplied `deerflow_trace_id` on the run
   record. `body.metadata` reaches both the live run config, which the run
   worker restamps, and the run record echoed verbatim by the runs API; only the
@@ -2678,3 +2688,4 @@ with **180 merged pull requests** since the first 2.0 milestone tag.
 [#5282]: https://github.com/bytedance/deer-flow/pull/5282
 [#5284]: https://github.com/bytedance/deer-flow/pull/5284
 [#5287]: https://github.com/bytedance/deer-flow/pull/5287
+[#5321]: https://github.com/bytedance/deer-flow/pull/5321
diff --git a/CHANGELOG_zh.md b/CHANGELOG_zh.md
index 6cfd804d3..c813874e1 100644
--- a/CHANGELOG_zh.md
+++ b/CHANGELOG_zh.md
@@ -392,6 +392,14 @@
 
 ### 修复
 
+- **Artifact：** `PUT /api/threads/{id}/artifacts/{path}` 现在严格限制在
+  `/mnt/user-data/outputs` 之内。此前 outputs-only 校验只是对原始路径做字符串前缀
+  检查，百分号编码的 `..`（`outputs/%2e%2e/uploads/x.txt`，nginx 原样转发、Starlette
+  解码后）可以通过，而路径解析器只把结果限制在 `user-data/` 内，因此调用者能覆盖自己
+  线程里的上传文件或 workspace 文件。现在会先折叠 `.`/`..` 段再做前缀检查，并把解析
+  后的宿主机路径与解析后的 outputs 根目录再次比对，`outputs/` 内被植入的符号链接同样
+  无法把写入重定向到别处。该规则现在收敛为一个共享 helper，IM 渠道的附件投递也走同
+  一实现，两处不会再各自漂移。([#5321])
 - **运行时：** 会话元数据现在仅在 run 通过启动屏障后才切换为 `running`，待取消的
   run 不再短暂呈现 `running` 状态；worker 启动期间客户端可能观察到先前的会话状态
   。([#4450])
@@ -2077,3 +2085,4 @@ DeerFlow 2.0 是围绕"超级智能体"框架的彻底重写，核心包含子
 [#5281]: https://github.com/bytedance/deer-flow/pull/5281
 [#5284]: https://github.com/bytedance/deer-flow/pull/5284
 [#5287]: https://github.com/bytedance/deer-flow/pull/5287
+[#5321]: https://github.com/bytedance/deer-flow/pull/5321
diff --git a/backend/app/channels/AGENTS.md b/backend/app/channels/AGENTS.md
index 7650d4877..ccc5e1e4a 100644
--- a/backend/app/channels/AGENTS.md
+++ b/backend/app/channels/AGENTS.md
@@ -42,7 +42,7 @@ Bridges external messaging platforms (Feishu, Slack, Telegram, Discord, DingTalk
 - `FeishuChannel._receive_single_file(...)` / `DingTalkChannel._receive_single_file(...)` — normalize provider filenames, claim a collision-free basename and write it through `write_upload_file_no_symlink` under the same channel lock; the returned basename drives both the agent-visible virtual path and non-local sandbox sync
 - `sandbox_files.py` — non-mounted Feishu/DingTalk syncs acquire unique non-releasing execution holders, drain blocking `update_file` workers across repeated cancellation, and release only after the last sandbox operation, so a parallel run cannot close the shared client mid-upload
 - `_ingest_inbound_files(...)` and the underlying `ensure_uploads_dir` / `get_uploads_dir` — owner-scoped via the same kwarg
-- `_resolve_attachments` / `_prepare_artifact_delivery` — resolve output artifacts from the bound owner's bucket
+- `_resolve_attachments` / `_prepare_artifact_delivery` — resolve output artifacts from the bound owner's bucket through `app.gateway.path_utils.resolve_outputs_confined_path`, the same outputs-only rule the artifact editor uses, so a sibling `uploads/`/`workspace/` path or a symlink planted in `outputs/` is skipped with a warning
 The cached value is reused for both the blocking (`runs.wait`) and streaming (`_handle_streaming_chat`) paths, so uploads and artifact delivery always target the same bucket even if a channel returns a rewritten `InboundMessage` from `receive_file`. The bucket id matches the memory bucket resolved by `_resolve_memory_user_id` (both normalize through `make_safe_user_id`).
 
 **Configuration** (`config.yaml` -> `channels`):
diff --git a/backend/app/channels/manager.py b/backend/app/channels/manager.py
index a17da6211..193dcd371 100644
--- a/backend/app/channels/manager.py
+++ b/backend/app/channels/manager.py
@@ -17,6 +17,7 @@ from typing import Any
 from urllib.parse import quote
 
 import httpx
+from fastapi import HTTPException
 from langgraph_sdk.errors import ConflictError
 
 from app.channels import buzz_run_policy as _buzz_run_policy  # noqa: F401
@@ -40,6 +41,7 @@ from app.gateway.csrf_middleware import CSRF_COOKIE_NAME, CSRF_HEADER_NAME, gene
 # ChannelManager construction sees the same policy map as gateway bootstrap.
 from app.gateway.github import run_policy as _github_run_policy  # noqa: F401
 from app.gateway.internal_auth import create_internal_auth_headers
+from app.gateway.path_utils import resolve_outputs_confined_path
 from deerflow.config.agents_config import list_custom_agents, load_agent_config
 from deerflow.config.paths import make_safe_user_id
 from deerflow.runtime import END_SENTINEL, StreamBridge
@@ -725,9 +727,6 @@ def _format_artifact_text(artifacts: list[str]) -> str:
     return "Created Files: 📎 " + "、".join(filenames)
 
 
-_OUTPUTS_VIRTUAL_PREFIX = "/mnt/user-data/outputs/"
-
-
 def _unknown_command_reply(command: str | None = None) -> str:
     available = " | ".join(sorted(KNOWN_CHANNEL_COMMANDS))
     if command:
@@ -848,26 +847,19 @@ def _resolve_attachments(thread_id: str, artifacts: list[str], *, user_id: str |
     Skips artifacts that cannot be resolved (missing files, invalid paths)
     and logs warnings for them.
     """
-    from deerflow.config.paths import get_paths
-
     attachments: list[ResolvedAttachment] = []
-    paths = get_paths()
     effective_user_id = user_id or get_effective_user_id()
-    outputs_dir = paths.sandbox_outputs_dir(thread_id, user_id=effective_user_id).resolve()
     for virtual_path in artifacts:
-        # Security: only allow files from the agent outputs directory
-        if not virtual_path.startswith(_OUTPUTS_VIRTUAL_PREFIX):
-            logger.warning("[Manager] rejected non-outputs artifact path: %s", virtual_path)
+        # Security: only files under the agent outputs directory may leave the
+        # thread. The shared helper rejects sibling ``uploads/``/``workspace/``
+        # paths both lexically (``..``) and after symlink resolution, so this
+        # rule cannot drift from the artifact editor's.
+        try:
+            actual = resolve_outputs_confined_path(thread_id, virtual_path, user_id=effective_user_id)
+        except HTTPException as exc:
+            logger.warning("[Manager] rejected artifact path outside outputs: %s (%s)", virtual_path, exc.detail)
             continue
         try:
-            actual = paths.resolve_virtual_path(thread_id, virtual_path, user_id=effective_user_id)
-            # Verify the resolved path is actually under the outputs directory
-            # (guards against path-traversal even after prefix check)
-            try:
-                actual.resolve().relative_to(outputs_dir)
-            except ValueError:
-                logger.warning("[Manager] artifact path escapes outputs dir: %s -> %s", virtual_path, actual)
-                continue
             if not actual.is_file():
                 logger.warning("[Manager] artifact not found on disk: %s -> %s", virtual_path, actual)
                 continue
diff --git a/backend/app/gateway/AGENTS.md b/backend/app/gateway/AGENTS.md
index eb624ac15..23d8bcecb 100644
--- a/backend/app/gateway/AGENTS.md
+++ b/backend/app/gateway/AGENTS.md
@@ -62,7 +62,7 @@ owner-scoped assistant version selection remains enabled.
 | **Memory** (`/api/memory`) | `GET /` - memory data; `POST /reload` - force reload; `GET /config` - config; `GET /status` - config + data |
 | **Uploads** (`/api/threads/{id}/uploads`) | `POST /` - upload files (auto-converts PDF/PPT/Excel/Word); non-mounted sandbox sync uses a non-releasing request lease; `GET /list` - list; `DELETE /{filename}` - delete |
 | **Threads** (`/api/threads/{id}`) | `DELETE /` - remove DeerFlow-managed local thread data after LangGraph thread deletion; `POST /branches` - branch a completed assistant turn with a replay checkpoint; inherited titles take next-free displayed sibling suffixes, including explicit/renamed ones, while explicit titles stay unchanged. Durable `branch` admission rejects races. Workspace files are not checkpointed, so the branch only best-effort copies the current workspace when branching from the **latest** turn (`workspace_clone_mode="current_thread_best_effort"`); branching from an older/historical turn skips the copy (`workspace_clone_mode="skipped_historical_turn"`) so the branch never inherits files that only exist in a later timeline. Thread-scoped runtime channels (`sandbox`, `thread_data`) are not copied onto the branch: the parent's `sandbox_id` binds path mappings and the release lifecycle to the parent's workspace, so the branch lazily acquires its own sandbox instead. Branch creation also seeds the new thread's run-event feed from the branch checkpoint's visible messages (`history_seed_mode` in the response): the thread feed reads run_events, not checkpoints, so without the seed the inherited history disappears from the UI after the branch's first run (#4380). Seeded rows are grouped into one synthetic run per inherited turn (`branch-seed-{thread_id}-{n}`, a new turn opening at every persisted human message, including an allowlisted hidden `ask_clarification` reply) because `run_id` is a turn identity to the feed's consumers, not a provenance tag: regenerating an inherited answer supersedes that row's whole `run_id` in `GET /messages/page`, so one shared id for the entire seed deleted the complete inherited history on a branch's first regenerate (#4458); `GET /goal`, `PUT /goal`, `DELETE /goal` - read, set, and clear the active thread goal; `POST /compact` - manually summarize older active context into `summary_text` and retain the recent message window, blocked while a run is in flight; unexpected failures are logged server-side and return a generic 500 detail |
-| **Artifacts** (`/api/threads/{id}/artifacts`) | `GET /{path}` - stream regular text and binary artifacts with `FileResponse`, including byte-`Range` 206/416 behavior used by bounded text previews and media seeking; active content types (`text/html`, `application/xhtml+xml`, `image/svg+xml`) are always forced as download attachments to reduce XSS risk; `?download=true` still forces download for other file types. `PUT /{path}` atomically replaces an existing UTF-8 text file under `/mnt/user-data/outputs` when its expected SHA-256 still matches; active runs conflict, and non-mounted sandbox providers receive the same update under a request lease. Atomic replacement applies the existing POSIX permission handling when descriptor-based APIs are available and otherwise keeps the platform-native temporary-file permissions (Windows). |
+| **Artifacts** (`/api/threads/{id}/artifacts`) | `GET /{path}` - stream regular text and binary artifacts with `FileResponse`, including byte-`Range` 206/416 behavior used by bounded text previews and media seeking; active content types (`text/html`, `application/xhtml+xml`, `image/svg+xml`) are always forced as download attachments to reduce XSS risk; `?download=true` still forces download for other file types. `PUT /{path}` atomically replaces an existing UTF-8 text file under `/mnt/user-data/outputs` when its expected SHA-256 still matches; active runs conflict, and non-mounted sandbox providers receive the same update under a request lease. The outputs-only rule is `path_utils.resolve_outputs_confined_path`, shared with IM-channel attachment delivery: it collapses `..` before the prefix check and re-checks the resolved host path against the resolved outputs root, since `resolve_thread_virtual_path` only confines to `user-data/`; a percent-encoded `..` or a symlink planted in `outputs/` must not reach a sibling `uploads/` file. Atomic replacement applies the existing POSIX permission handling when descriptor-based APIs are available and otherwise keeps the platform-native temporary-file permissions (Windows). |
 | **Suggestions** (`/api/suggestions`) | `GET /config` - returns global suggestions config boolean; `POST /threads/{id}/suggestions` - generate follow-up questions; rich list/block model content is normalized and inline reasoning (`<think>...</think>`, including unclosed/truncated blocks from reasoning models like MiniMax-M3) is stripped before JSON parsing |
 | **Input Polish** (`/api/input-polish`) | `POST /` - rewrite a composer draft before it is sent. This is a short authenticated `runs:create` LLM request using `input_polish` config; it does not create a LangGraph run, persist a message, or modify thread state. Shares the non-graph one-shot LLM path (`deerflow.utils.oneshot_llm.run_oneshot_llm`) with the suggestions route so model build + Langfuse metadata + invoke stay in one place; validates the same stripped view of the draft it sends to the model, and preserves literal `<think>` substrings in the rewrite (`strip_think_blocks(truncate_unclosed=False)`) |
 | **Thread Runs** (`/api/threads/{id}/runs`) | `POST /` - create background run; `POST /stream` - create + SSE stream; `POST /wait` - create + block. Before the first journaled run, seed an empty feed from a checkpoint so legacy checkpoint-only history keeps its order and visibility; skip absent checkpoints or populated feeds. `POST /regenerate/prepare` - prepare clean input + checkpoint metadata for regenerating the latest completed or interrupted assistant answer, carrying the latest non-empty thread title in graph input so resuming an older checkpoint cannot roll back a later manual rename (#4457); `POST /edit-regenerate/prepare` - prepare a checkpoint replay from the latest editable human turn with a replacement user message and edit replay metadata; it carries the current thread title the same way, but only when the replay base already has one — an untitled base belongs to a thread the title middleware has not named yet, so pinning the current title there would keep a name generated from the prompt the edit just replaced; `GET /` - newest 100 runs as an array; `GET /page` - keyset history page `{data, has_more, next_before_created_at, next_before_run_id}`; `GET /{rid}` - run details; `POST /{rid}/cancel` - cancel; `GET /{rid}/join` - join SSE; `GET /{rid}/stream` hides action/wait; GET action 405 pre-owner; POST needs `runs:cancel`; `GET /{rid}/messages` - paginated per-run messages `{data, has_more}`; `GET /{rid}/events` - full event stream; `GET /{rid}/workspace-changes` - workspace/output file change summary and optional diffs; `GET/POST /{rid}/artifacts/archive` - receipt manifest / bounded ZIP; `GET /../messages` - legacy thread message array; `GET /../messages/page` - backward thread-global `seq` history page with middleware/subagent-AI/successful-regenerate/edit-replay filtering and page-run-scoped feedback enrichment; subagent AI callbacks remain available through run events while parent `task` ToolMessages stay visible for card restoration; `GET /../token-usage` - aggregate tokens plus an optional `context_usage` percentage. Context usage approximately counts messages from the latest materialized thread state through `build_thread_checkpoint_state_accessor`, so full and delta checkpoint modes expose the same input. The percentage uses the latest run's model and its `context_window`. |
diff --git a/backend/app/gateway/path_utils.py b/backend/app/gateway/path_utils.py
index 43f4f9abc..c501e9a76 100644
--- a/backend/app/gateway/path_utils.py
+++ b/backend/app/gateway/path_utils.py
@@ -1,12 +1,17 @@
 """Shared path resolution for thread virtual paths (e.g. mnt/user-data/outputs/...)."""
 
+import posixpath
 from pathlib import Path
 
 from fastapi import HTTPException
 
-from deerflow.config.paths import get_paths
+from deerflow.config.paths import VIRTUAL_PATH_PREFIX, get_paths
 from deerflow.runtime.user_context import get_effective_user_id
 
+OUTPUTS_VIRTUAL_ROOT = f"{VIRTUAL_PATH_PREFIX}/outputs"
+_OUTPUTS_PREFIX = OUTPUTS_VIRTUAL_ROOT.lstrip("/") + "/"
+_OUTPUTS_ONLY_DETAIL = f"Only files under {OUTPUTS_VIRTUAL_ROOT} are allowed"
+
 
 def resolve_thread_virtual_path(thread_id: str, virtual_path: str, user_id: str | None = None) -> Path:
     """Resolve a virtual path to the actual filesystem path under thread user-data.
@@ -30,3 +35,46 @@ def resolve_thread_virtual_path(thread_id: str, virtual_path: str, user_id: str
     except ValueError as e:
         status = 403 if "traversal" in str(e) else 400
         raise HTTPException(status_code=status, detail=str(e))
+
+
+def normalize_outputs_virtual_path(virtual_path: str) -> str:
+    """Return *virtual_path* as a canonical ``/mnt/user-data/outputs/...`` path.
+
+    ``.``/``..`` segments and duplicate slashes are collapsed *before* the
+    prefix check, so ``outputs/../uploads/x`` (or its percent-encoded form,
+    which nginx forwards untouched and Starlette decodes) is rejected as a
+    non-outputs path instead of slipping past a raw string-prefix test. The
+    outputs directory itself is not a file and is rejected too.
+
+    Raises:
+        HTTPException: 400 when the path is not strictly inside outputs.
+    """
+    stripped = posixpath.normpath(virtual_path.lstrip("/")).lstrip("/")
+    if not stripped.startswith(_OUTPUTS_PREFIX):
+        raise HTTPException(status_code=400, detail=_OUTPUTS_ONLY_DETAIL)
+    return f"/{stripped}"
+
+
+def resolve_outputs_confined_path(thread_id: str, virtual_path: str, user_id: str | None = None) -> Path:
+    """Resolve *virtual_path* and guarantee it lives inside the thread's outputs dir.
+
+    ``resolve_thread_virtual_path`` only confines to ``user-data/``. Callers
+    that must never touch uploads, workspace, or tool results (the artifact
+    editor, IM-channel attachment delivery) go through this helper so the
+    outputs rule lives in one place: the path is normalized lexically first,
+    then the resolved host path is checked against the resolved outputs root,
+    which also catches a symlink planted inside ``outputs/``.
+
+    Existence is not checked; callers decide how a missing file surfaces.
+
+    Raises:
+        HTTPException: 400 when the path is not strictly inside outputs; 403
+            when the underlying resolver detects traversal above ``user-data/``.
+    """
+    normalized = normalize_outputs_virtual_path(virtual_path)
+    resolved_user_id = user_id or get_effective_user_id()
+    actual_path = resolve_thread_virtual_path(thread_id, normalized, user_id=resolved_user_id)
+    outputs_root = get_paths().sandbox_outputs_dir(thread_id, user_id=resolved_user_id).resolve()
+    if actual_path == outputs_root or not actual_path.is_relative_to(outputs_root):
+        raise HTTPException(status_code=400, detail=_OUTPUTS_ONLY_DETAIL)
+    return actual_path
diff --git a/backend/app/gateway/routers/artifacts.py b/backend/app/gateway/routers/artifacts.py
index f304af728..eb19c7cf3 100644
--- a/backend/app/gateway/routers/artifacts.py
+++ b/backend/app/gateway/routers/artifacts.py
@@ -19,7 +19,7 @@ from pydantic import BaseModel, Field
 from app.gateway.authz import SandboxRequestLease, require_permission, try_acquire_sandbox_for_request
 from app.gateway.deps import get_run_manager
 from app.gateway.internal_auth import get_trusted_internal_owner_user_id
-from app.gateway.path_utils import resolve_thread_virtual_path
+from app.gateway.path_utils import normalize_outputs_virtual_path, resolve_outputs_confined_path, resolve_thread_virtual_path
 from deerflow.authz.sandbox_authz import safe_app_config
 from deerflow.config.paths import make_safe_user_id
 from deerflow.runtime import ConflictError, ThreadOperationKind
@@ -40,7 +40,6 @@ ACTIVE_CONTENT_MIME_TYPES = {
 MAX_SKILL_ARCHIVE_MEMBER_BYTES = 16 * 1024 * 1024
 _SKILL_ARCHIVE_READ_CHUNK_SIZE = 64 * 1024
 MAX_EDITABLE_ARTIFACT_BYTES = 2 * 1024 * 1024
-_EDITABLE_OUTPUTS_PREFIX = "mnt/user-data/outputs/"
 _ARTIFACT_EDIT_TEMP_PREFIX = ".artifact-edit-"
 
 
@@ -68,12 +67,15 @@ async def reserve_artifact_write(request: Request, thread_id: str, *, user_id: s
 
 
 def _normalize_editable_artifact_path(path: str) -> str:
-    stripped = path.lstrip("/")
-    if not stripped.startswith(_EDITABLE_OUTPUTS_PREFIX):
-        raise HTTPException(status_code=400, detail="Only files in /mnt/user-data/outputs can be edited")
-    if ".skill/" in stripped or stripped.endswith(".skill"):
+    # The outputs-only rule is shared with channel attachment delivery:
+    # ``normalize_outputs_virtual_path`` collapses ``..`` before its prefix check
+    # and ``resolve_outputs_confined_path`` re-checks the resolved host path, so
+    # neither an encoded ``..`` nor a symlink planted in ``outputs/`` can
+    # redirect the edit to a sibling ``user-data/`` directory.
+    virtual_path = normalize_outputs_virtual_path(path)
+    if ".skill/" in virtual_path or virtual_path.endswith(".skill"):
         raise HTTPException(status_code=415, detail="Skill archives cannot be edited in the artifacts panel")
-    return f"/{stripped}"
+    return virtual_path
 
 
 def _load_editable_artifact(actual_path: Path, path: str, expected_sha256: str) -> tuple[bytes, os.stat_result]:
@@ -516,7 +518,7 @@ async def update_artifact(
     try:
         async with reserve_artifact_write(request, thread_id, user_id=effective_user_id):
             actual_path = await asyncio.to_thread(
-                resolve_thread_virtual_path,
+                resolve_outputs_confined_path,
                 thread_id,
                 virtual_path,
                 user_id=effective_user_id,
diff --git a/backend/tests/test_artifacts_router.py b/backend/tests/test_artifacts_router.py
index a2f8f1b96..8d7987beb 100644
--- a/backend/tests/test_artifacts_router.py
+++ b/backend/tests/test_artifacts_router.py
@@ -15,7 +15,7 @@ from starlette.responses import FileResponse
 
 import app.gateway.routers.artifacts as artifacts_router
 from app.gateway.internal_auth import INTERNAL_OWNER_USER_ID_HEADER_NAME, INTERNAL_SYSTEM_ROLE
-from deerflow.config.paths import make_safe_user_id
+from deerflow.config.paths import Paths, make_safe_user_id
 from deerflow.sandbox.lease import get_sandbox_lease_manager
 
 ACTIVE_ARTIFACT_CASES = [
@@ -102,7 +102,7 @@ def _artifact_sha256(content: str) -> str:
 
 
 def _patch_artifact_update_dependencies(monkeypatch, artifact_path: Path, provider=None) -> None:
-    monkeypatch.setattr(artifacts_router, "resolve_thread_virtual_path", lambda _thread_id, _path, user_id=None: artifact_path)
+    monkeypatch.setattr(artifacts_router, "resolve_outputs_confined_path", lambda _thread_id, _path, user_id=None: artifact_path)
     monkeypatch.setattr(artifacts_router, "reserve_artifact_write", _allow_artifact_write)
     monkeypatch.setattr(artifacts_router, "get_sandbox_provider", lambda: provider or _MountedSandboxProvider())
 
@@ -193,6 +193,107 @@ def test_update_artifact_rejects_non_output_path(tmp_path, monkeypatch) -> None:
     assert artifact_path.read_text(encoding="utf-8") == "before"
 
 
+_REAL_PATHS_THREAD_ID = "thread-1"
+_REAL_PATHS_USER_ID = "user-1"
+
+
+def _patch_real_thread_paths(monkeypatch, tmp_path: Path, provider=None) -> tuple[Path, Path]:
+    """Route ``update_artifact`` through the real virtual-path resolver rooted at *tmp_path*.
+
+    The other update tests stub ``resolve_outputs_confined_path`` so they never
+    exercise the outputs confinement; these tests need the real thread layout.
+    Returns the thread's ``outputs`` and ``uploads`` host directories.
+    """
+    paths = Paths(tmp_path)
+    monkeypatch.setattr("app.gateway.path_utils.get_paths", lambda: paths)
+    monkeypatch.setattr(artifacts_router, "get_effective_user_id", lambda: _REAL_PATHS_USER_ID)
+    monkeypatch.setattr(artifacts_router, "get_trusted_internal_owner_user_id", lambda _request: None)
+    monkeypatch.setattr(artifacts_router, "reserve_artifact_write", _allow_artifact_write)
+    monkeypatch.setattr(artifacts_router, "get_sandbox_provider", lambda: provider or _MountedSandboxProvider())
+
+    outputs = paths.sandbox_outputs_dir(_REAL_PATHS_THREAD_ID, user_id=_REAL_PATHS_USER_ID)
+    uploads = paths.sandbox_uploads_dir(_REAL_PATHS_THREAD_ID, user_id=_REAL_PATHS_USER_ID)
+    outputs.mkdir(parents=True)
+    uploads.mkdir(parents=True)
+    return outputs, uploads
+
+
+def _update_artifact_via_handler(path: str, *, current: str, content: str):
+    return asyncio.run(
+        call_unwrapped(
+            artifacts_router.update_artifact,
+            _REAL_PATHS_THREAD_ID,
+            path,
+            artifacts_router.ArtifactUpdateRequest(content=content, expected_sha256=_artifact_sha256(current)),
+            _make_request(),
+        )
+    )
+
+
+def test_update_artifact_rejects_dot_dot_escape_from_outputs(tmp_path, monkeypatch) -> None:
+    # The outputs-only guard used to be a string-prefix check on the raw path,
+    # so ``outputs/../uploads/...`` passed it and the resolver only confines to
+    # ``user-data/`` — letting PUT overwrite a sibling upload.
+    _, uploads = _patch_real_thread_paths(monkeypatch, tmp_path)
+    victim = uploads / "victim.txt"
+    victim.write_text("before", encoding="utf-8")
+
+    with pytest.raises(HTTPException) as exc_info:
+        _update_artifact_via_handler("mnt/user-data/outputs/../uploads/victim.txt", current="before", content="after")
+
+    assert exc_info.value.status_code == 400
+    assert victim.read_text(encoding="utf-8") == "before"
+
+
+def test_update_artifact_rejects_percent_encoded_dot_dot_over_http(tmp_path, monkeypatch) -> None:
+    # Browsers and HTTP clients collapse a literal ``..`` before sending, but
+    # ``%2e%2e`` reaches the route intact and Starlette decodes it to ``..``.
+    _, uploads = _patch_real_thread_paths(monkeypatch, tmp_path)
+    victim = uploads / "victim.txt"
+    victim.write_text("before", encoding="utf-8")
+
+    app = make_authed_test_app()
+    app.include_router(artifacts_router.router)
+    with TestClient(app) as client:
+        response = client.put(
+            f"/api/threads/{_REAL_PATHS_THREAD_ID}/artifacts/mnt/user-data/outputs/%2e%2e/uploads/victim.txt",
+            json={"content": "after", "expected_sha256": _artifact_sha256("before")},
+        )
+
+    assert response.status_code == 400
+    assert victim.read_text(encoding="utf-8") == "before"
+
+
+def test_update_artifact_rejects_symlink_escaping_outputs(tmp_path, monkeypatch) -> None:
+    outputs, uploads = _patch_real_thread_paths(monkeypatch, tmp_path)
+    victim = uploads / "victim.txt"
+    victim.write_text("before", encoding="utf-8")
+    link = outputs / "linked.txt"
+    try:
+        link.symlink_to(victim)
+    except OSError:
+        pytest.skip("symlinks are unavailable on this platform")
+
+    with pytest.raises(HTTPException) as exc_info:
+        _update_artifact_via_handler("mnt/user-data/outputs/linked.txt", current="before", content="after")
+
+    assert exc_info.value.status_code == 400
+    assert victim.read_text(encoding="utf-8") == "before"
+
+
+def test_update_artifact_normalizes_dot_segments_before_syncing(tmp_path, monkeypatch) -> None:
+    provider = _RemoteSandboxProvider()
+    outputs, _ = _patch_real_thread_paths(monkeypatch, tmp_path, provider=provider)
+    artifact_path = outputs / "note.txt"
+    artifact_path.write_text("before", encoding="utf-8")
+
+    response = _update_artifact_via_handler("mnt/user-data/outputs/./nested/../note.txt", current="before", content="after")
+
+    assert artifact_path.read_text(encoding="utf-8") == "after"
+    assert response.path == "/mnt/user-data/outputs/note.txt"
+    assert provider.sandbox.updates == [("/mnt/user-data/outputs/note.txt", b"after")]
+
+
 def test_update_artifact_rejects_binary_file(tmp_path, monkeypatch) -> None:
     artifact_path = tmp_path / "blob.bin"
     artifact_path.write_bytes(b"before\x00binary")
diff --git a/backend/tests/test_channel_file_attachments.py b/backend/tests/test_channel_file_attachments.py
index 0b8e27496..cce5983c1 100644
--- a/backend/tests/test_channel_file_attachments.py
+++ b/backend/tests/test_channel_file_attachments.py
@@ -7,6 +7,8 @@ import os
 from pathlib import Path
 from unittest.mock import MagicMock, patch
 
+import pytest
+
 from app.channels.base import Channel
 from app.channels.message_bus import InboundMessage, MessageBus, OutboundMessage, ResolvedAttachment
 
@@ -116,7 +118,7 @@ class TestResolveAttachments:
         mock_paths.resolve_virtual_path.return_value = test_file
         mock_paths.sandbox_outputs_dir.return_value = outputs_dir
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments(thread_id, ["/mnt/user-data/outputs/report.pdf"])
 
         assert len(result) == 1
@@ -139,7 +141,7 @@ class TestResolveAttachments:
         mock_paths.resolve_virtual_path.return_value = img
         mock_paths.sandbox_outputs_dir.return_value = outputs_dir
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments(thread_id, ["/mnt/user-data/outputs/chart.png"])
 
         assert len(result) == 1
@@ -157,7 +159,7 @@ class TestResolveAttachments:
         mock_paths.resolve_virtual_path.return_value = outputs_dir / "nonexistent.txt"
         mock_paths.sandbox_outputs_dir.return_value = outputs_dir
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments("t1", ["/mnt/user-data/outputs/nonexistent.txt"])
 
         assert result == []
@@ -169,7 +171,7 @@ class TestResolveAttachments:
         mock_paths = MagicMock()
         mock_paths.resolve_virtual_path.side_effect = ValueError("bad path")
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments("t1", ["/invalid/path"])
 
         assert result == []
@@ -180,7 +182,7 @@ class TestResolveAttachments:
 
         mock_paths = MagicMock()
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments("t1", ["/mnt/user-data/uploads/secret.pdf"])
 
         assert result == []
@@ -192,7 +194,7 @@ class TestResolveAttachments:
 
         mock_paths = MagicMock()
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments("t1", ["/mnt/user-data/workspace/config.py"])
 
         assert result == []
@@ -214,11 +216,37 @@ class TestResolveAttachments:
         mock_paths.resolve_virtual_path.return_value = escaped_file
         mock_paths.sandbox_outputs_dir.return_value = outputs_dir
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments(thread_id, ["/mnt/user-data/outputs/../uploads/stolen.txt"])
 
         assert result == []
 
+    def test_rejects_symlink_planted_in_outputs(self, tmp_path):
+        """A symlink inside outputs/ pointing at a sibling upload is skipped.
+
+        Uses the real ``Paths`` layout so the shared outputs-confinement helper
+        (also used by the artifact editor) is exercised end to end.
+        """
+        from app.channels.manager import _resolve_attachments
+        from deerflow.config.paths import Paths
+
+        paths = Paths(tmp_path)
+        outputs_dir = paths.sandbox_outputs_dir("t1", user_id="owner-1")
+        uploads_dir = paths.sandbox_uploads_dir("t1", user_id="owner-1")
+        outputs_dir.mkdir(parents=True)
+        uploads_dir.mkdir(parents=True)
+        victim = uploads_dir / "secret.pdf"
+        victim.write_bytes(b"%PDF-1.4 secret")
+        try:
+            (outputs_dir / "report.pdf").symlink_to(victim)
+        except OSError:
+            pytest.skip("symlinks are unavailable on this platform")
+
+        with patch("app.gateway.path_utils.get_paths", return_value=paths):
+            result = _resolve_attachments("t1", ["/mnt/user-data/outputs/report.pdf"], user_id="owner-1")
+
+        assert result == []
+
     def test_multiple_artifacts_partial_resolution(self, tmp_path):
         """Mixed valid/invalid artifacts: only valid ones are returned."""
         from app.channels.manager import _resolve_attachments
@@ -239,7 +267,7 @@ class TestResolveAttachments:
 
         mock_paths.resolve_virtual_path.side_effect = resolve_side_effect
 
-        with patch("deerflow.config.paths.get_paths", return_value=mock_paths):
+        with patch("app.gateway.path_utils.get_paths", return_value=mock_paths):
             result = _resolve_attachments(
                 thread_id,
                 ["/mnt/user-data/outputs/data.csv", "/mnt/user-data/outputs/missing.txt"],
diff --git a/backend/tests/test_channels.py b/backend/tests/test_channels.py
index 971089b90..7611a6fc5 100644
--- a/backend/tests/test_channels.py
+++ b/backend/tests/test_channels.py
@@ -5707,6 +5707,9 @@ class TestHandleChatWithArtifacts:
 
         paths = Paths(tmp_path)
         monkeypatch.setattr("deerflow.config.paths.get_paths", lambda: paths)
+        # Attachment resolution goes through the shared outputs-confinement
+        # helper, which binds ``get_paths`` at import like the other consumers.
+        monkeypatch.setattr("app.gateway.path_utils.get_paths", lambda: paths)
         outputs_dir = paths.sandbox_outputs_dir("test-thread-123", user_id="owner-1")
         outputs_dir.mkdir(parents=True)
         (outputs_dir / "report.md").write_text("owner report", encoding="utf-8")
diff --git a/backend/tests/test_gateway_path_utils.py b/backend/tests/test_gateway_path_utils.py
new file mode 100644
index 000000000..146ca8b76
--- /dev/null
+++ b/backend/tests/test_gateway_path_utils.py
@@ -0,0 +1,145 @@
+"""Tests for the shared outputs-confinement helpers in ``app.gateway.path_utils``.
+
+The artifact editor (``PUT /artifacts``) and IM-channel attachment delivery
+both must never touch anything outside ``/mnt/user-data/outputs``. The rule
+used to be re-implemented per caller; these tests pin the single shared
+implementation so the copies cannot drift again.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from fastapi import HTTPException
+
+from app.gateway.path_utils import OUTPUTS_VIRTUAL_ROOT, normalize_outputs_virtual_path, resolve_outputs_confined_path
+from deerflow.config.paths import Paths
+
+THREAD_ID = "thread-1"
+USER_ID = "user-1"
+
+
+@pytest.fixture
+def thread_dirs(tmp_path, monkeypatch) -> tuple[Path, Path]:
+    """Point the global ``Paths`` at *tmp_path* and return (outputs, uploads)."""
+    paths = Paths(tmp_path)
+    monkeypatch.setattr("app.gateway.path_utils.get_paths", lambda: paths)
+    outputs = paths.sandbox_outputs_dir(THREAD_ID, user_id=USER_ID)
+    uploads = paths.sandbox_uploads_dir(THREAD_ID, user_id=USER_ID)
+    outputs.mkdir(parents=True)
+    uploads.mkdir(parents=True)
+    return outputs, uploads
+
+
+def _symlink_or_skip(link: Path, target: Path) -> None:
+    try:
+        link.symlink_to(target)
+    except OSError:
+        pytest.skip("symlinks are unavailable on this platform")
+
+
+class TestNormalizeOutputsVirtualPath:
+    def test_returns_canonical_absolute_virtual_path(self) -> None:
+        assert normalize_outputs_virtual_path("mnt/user-data/outputs/report.md") == "/mnt/user-data/outputs/report.md"
+        assert normalize_outputs_virtual_path("//mnt/user-data/outputs//a/./b.txt") == "/mnt/user-data/outputs/a/b.txt"
+
+    def test_collapses_dot_dot_that_stays_inside_outputs(self) -> None:
+        assert normalize_outputs_virtual_path("/mnt/user-data/outputs/nested/../note.txt") == "/mnt/user-data/outputs/note.txt"
+
+    @pytest.mark.parametrize(
+        "virtual_path",
+        [
+            "/mnt/user-data/uploads/secret.pdf",
+            "/mnt/user-data/workspace/config.py",
+            "/mnt/user-data/outputs/../uploads/secret.pdf",
+            "/mnt/user-data/outputsX/file.txt",
+            "/mnt/user-data/outputs",
+            "/mnt/user-data/outputs/",
+            "/invalid/path",
+            "",
+        ],
+    )
+    def test_rejects_paths_outside_outputs(self, virtual_path: str) -> None:
+        with pytest.raises(HTTPException) as exc_info:
+            normalize_outputs_virtual_path(virtual_path)
+        assert exc_info.value.status_code == 400
+
+    def test_root_constant_matches_prefix(self) -> None:
+        assert OUTPUTS_VIRTUAL_ROOT == "/mnt/user-data/outputs"
+
+
+class TestResolveOutputsConfinedPath:
+    def test_resolves_regular_file_under_outputs(self, thread_dirs) -> None:
+        outputs, _ = thread_dirs
+        target = outputs / "report.md"
+        target.write_text("hello", encoding="utf-8")
+
+        resolved = resolve_outputs_confined_path(THREAD_ID, "/mnt/user-data/outputs/report.md", user_id=USER_ID)
+
+        assert resolved == target.resolve()
+
+    def test_does_not_require_the_file_to_exist(self, thread_dirs) -> None:
+        # Existence is the caller's decision (the editor 404s, channels warn).
+        outputs, _ = thread_dirs
+
+        resolved = resolve_outputs_confined_path(THREAD_ID, "/mnt/user-data/outputs/missing.txt", user_id=USER_ID)
+
+        assert resolved == (outputs / "missing.txt").resolve()
+
+    def test_rejects_dot_dot_escape_lexically(self, thread_dirs) -> None:
+        _, uploads = thread_dirs
+        (uploads / "victim.txt").write_text("before", encoding="utf-8")
+
+        with pytest.raises(HTTPException) as exc_info:
+            resolve_outputs_confined_path(THREAD_ID, "/mnt/user-data/outputs/../uploads/victim.txt", user_id=USER_ID)
+
+        assert exc_info.value.status_code == 400
+
+    def test_rejects_symlink_pointing_at_sibling_directory(self, thread_dirs) -> None:
+        outputs, uploads = thread_dirs
+        victim = uploads / "victim.txt"
+        victim.write_text("before", encoding="utf-8")
+        _symlink_or_skip(outputs / "linked.txt", victim)
+
+        with pytest.raises(HTTPException) as exc_info:
+            resolve_outputs_confined_path(THREAD_ID, "/mnt/user-data/outputs/linked.txt", user_id=USER_ID)
+
+        assert exc_info.value.status_code == 400
+
+    def test_symlink_escaping_user_data_is_a_traversal(self, thread_dirs, tmp_path) -> None:
+        # Above ``user-data/`` the underlying resolver already refuses; that 403
+        # must not be downgraded by the outputs check layered on top.
+        outputs, _ = thread_dirs
+        outside = tmp_path / "outside.txt"
+        outside.write_text("outside", encoding="utf-8")
+        _symlink_or_skip(outputs / "linked.txt", outside)
+
+        with pytest.raises(HTTPException) as exc_info:
+            resolve_outputs_confined_path(THREAD_ID, "/mnt/user-data/outputs/linked.txt", user_id=USER_ID)
+
+        assert exc_info.value.status_code == 403
+
+    def test_symlinked_outputs_root_outside_user_data_is_a_traversal(self, thread_dirs, tmp_path) -> None:
+        # An outputs root re-pointed outside ``user-data/`` is refused by the
+        # underlying resolver (matching ``artifact_archive``), not accepted
+        # because both sides happen to resolve consistently.
+        outputs, _ = thread_dirs
+        real_outputs = tmp_path / "real-outputs"
+        real_outputs.mkdir()
+        (real_outputs / "report.md").write_text("hello", encoding="utf-8")
+        outputs.rmdir()
+        _symlink_or_skip(outputs, real_outputs)
+
+        with pytest.raises(HTTPException) as exc_info:
+            resolve_outputs_confined_path(THREAD_ID, "/mnt/user-data/outputs/report.md", user_id=USER_ID)
+
+        assert exc_info.value.status_code == 403
+
+    def test_defaults_to_effective_user(self, thread_dirs, monkeypatch) -> None:
+        outputs, _ = thread_dirs
+        monkeypatch.setattr("app.gateway.path_utils.get_effective_user_id", lambda: USER_ID)
+
+        resolved = resolve_outputs_confined_path(THREAD_ID, "/mnt/user-data/outputs/report.md")
+
+        assert resolved == (outputs / "report.md").resolve()
diff --git a/backend/tests/test_sandbox_authorization.py b/backend/tests/test_sandbox_authorization.py
index dad3cf9a1..0f2f398b9 100644
--- a/backend/tests/test_sandbox_authorization.py
+++ b/backend/tests/test_sandbox_authorization.py
@@ -561,7 +561,7 @@ def test_artifact_sandbox_sync_skipped_when_denied(monkeypatch, tmp_path):
     sandbox_provider.uses_thread_data_mounts = False
     sandbox_provider.acquire_async = AsyncMock(side_effect=AssertionError("must not acquire"))
     monkeypatch.setattr(artifacts_router, "get_sandbox_provider", lambda: sandbox_provider)
-    monkeypatch.setattr(artifacts_router, "resolve_thread_virtual_path", lambda _t, _p, user_id=None: tmp_path / "note.txt")
+    monkeypatch.setattr(artifacts_router, "resolve_outputs_confined_path", lambda _t, _p, user_id=None: tmp_path / "note.txt")
 
     from contextlib import asynccontextmanager