fix(channels): scope IM files and helper commands to owner (#3579)

* fix(channels): scope IM files and helper commands to owner

* fix(memory): honor bound IM owner for /memory gateway endpoints

The channel manager already attaches X-DeerFlow-Owner-User-Id for /memory
and /models, but the memory router resolved user_id solely from
get_effective_user_id(), which returns the synthetic internal user
(DEFAULT_USER_ID) for channel workers. A bound IM /memory therefore read
the default/internal memory instead of the connection owner's.

Resolve the owner via _resolve_memory_user_id(request) across all
/api/memory* endpoints: trusted internal callers act for the owner header,
browser/API callers fall back to get_effective_user_id(). Mirrors the
threads router's get_trusted_internal_owner_user_id pattern, completing
acceptance criterion #3 of #3539.

Add end-to-end tests asserting the resolved user_id (not just that the
header is sent) and that a spoofed owner header from a browser user is
ignored.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(channels): align memory bucket and reuse cached storage owner

Address PR #3579 review feedback:

- Memory router now sanitizes the trusted owner header via make_safe_user_id
  before routing, matching the channel file pipeline
  (_safe_user_id_for_run/prepare_user_dir_for_raw_id). A bound owner id needing
  sanitization now resolves to the same bucket as its files/uploads instead of
  500ing in _validate_user_id.
- _handle_chat reuses the storage_user_id cached at the top of the method for
  artifact delivery instead of re-deriving _channel_storage_user_id(msg), so
  uploads and outputs cannot drift to different buckets if a channel rewrites
  the InboundMessage in receive_file.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(channels): stage unbound IM files under the run's user bucket

Address PR #3579 review feedback (#5): _channel_storage_user_id now mirrors
_resolve_run_params' identity policy, falling back to safe(msg.user_id) instead
of returning None for unbound auth-enabled channels.

Previously an unbound msg ran under safe(platform_user_id) but staged uploads
under get_effective_user_id() in the dispatcher task (unset contextvar ->
"default"), so files landed in users/default/... while the agent read from
users/{safe_platform_user_id}/.... Bound and unbound channels now write where
the agent reads. Returns None only when no identity is available.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(channels): reuse cached storage owner in streaming artifact delivery

Address PR #3579 review feedback (#6): thread the storage_user_id resolved in
_handle_chat into _handle_streaming_chat instead of re-deriving
_channel_storage_user_id(msg) in the finally block. Avoids re-running
_safe_user_id_for_run (and its possible filesystem touch) on the streaming-error
path and guarantees artifact delivery targets the same bucket as the uploads.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* docs(channels): document owner-scoped IM file storage

Address PR #3579 review feedback (#4): the IM Channels and File Upload sections
still described pre-PR default-bucket behaviour. Document that receive_file,
_ingest_inbound_files/ensure_uploads_dir/get_uploads_dir, and
_resolve_attachments/_prepare_artifact_delivery are owner-scoped via the user_id
kwarg, and that the bucket matches the memory bucket from _resolve_memory_user_id.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* refactor(channels): unify run identity and storage bucket resolution

Address PR #3579 review feedback (#3): _resolve_run_params no longer duplicates
the owner-resolution rule inline. After the #5 fix the inline block and
_channel_storage_user_id computed the identical sanitized-with-platform-fallback
value, so the run identity now calls the same helper, making it the single
source of truth for run_context["user_id"] and the file/artifact storage bucket.

_owner_headers stays deliberately separate: it sends the raw owner id over HTTP
for the gateway to re-resolve (no sanitize, no platform fallback), documented on
both helpers. test_run_identity_matches_storage_bucket pins the two together so
they cannot drift again.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/channels/base.py

@@ -178,7 +178,7 @@ class Channel(ABC):
                 except Exception:
                     logger.exception("[%s] failed to upload file %s", self.name, attachment.filename)
 
-    async def receive_file(self, msg: InboundMessage, thread_id: str) -> InboundMessage:
+    async def receive_file(self, msg: InboundMessage, thread_id: str, *, user_id: str | None = None) -> InboundMessage:
         """
         Optionally process and materialize inbound file attachments for this channel.
 
@@ -190,8 +190,10 @@ class Channel(ABC):
         Args:
             msg: The inbound message, possibly containing file metadata in msg.files.
             thread_id: The resolved DeerFlow thread ID for sandbox path context.
+            user_id: Optional DeerFlow storage user ID for user-scoped channel workers.
 
         Returns:
             The (possibly modified) InboundMessage, with text and/or files updated as needed.
         """
+        del user_id
         return msg