How to upload files and share them with subagents?

[astromaier (asmaier)]

Is there a canonical way on how to upload files to an agent and share the files with subagents? It seems that file data is stripped from the context, when a subagent is initialized. So is the only way to do it via a FilesystemBackend?

[Barry (barry166)]

Yes, use the DeepAgents filesystem/backend as the handoff point. Subagents are intentionally started with isolated context windows, and the subagent middleware excludes messages when building the subagent state, so file/blob data that only lives in the chat/message context is not something to rely on for delegation.

The usual pattern is: upload or decode the file in the parent, write it to the agent filesystem (write_file or your app-side backend write), then call task(...) with the path and instructions. create_deep_agent(..., backend=...) wires the same backend into the parent FilesystemMiddleware and the declarative subagents' FilesystemMiddleware, so a FilesystemBackend, StateBackend, StoreBackend, etc. is the canonical bridge.

So for local/dev usage, FilesystemBackend(root_dir=...) is fine; for a hosted app, prefer a state/store/sandbox backend and pass stable paths/ids to the subagent rather than trying to pass uploaded file contents through the subagent prompt.