Address IM channel review comments

backend/app/channels/connection_identity.py

@@ -0,0 +1,44 @@
+"""Helpers for attaching persisted channel connection ownership to inbound messages."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from app.channels.message_bus import InboundMessage
+
+
+async def attach_connection_identity(
+    inbound: InboundMessage,
+    *,
+    repo: Any,
+    provider: str,
+    workspace_id: str | None,
+    fallback_without_workspace: bool = False,
+) -> InboundMessage:
+    """Attach connection metadata to an inbound message when a persisted binding exists."""
+    if repo is None:
+        return inbound
+
+    workspace_candidates: list[str | None] = []
+    if workspace_id:
+        workspace_candidates.append(workspace_id)
+    if fallback_without_workspace:
+        workspace_candidates.append(None)
+    if not workspace_candidates:
+        return inbound
+
+    for candidate in workspace_candidates:
+        connection = await repo.find_connection_by_external_identity(
+            provider=provider,
+            external_account_id=inbound.user_id,
+            workspace_id=candidate,
+        )
+        if connection is None:
+            continue
+
+        inbound.connection_id = connection["id"]
+        inbound.owner_user_id = connection["owner_user_id"]
+        inbound.workspace_id = connection.get("workspace_id")
+        return inbound
+
+    return inbound