OMA output_file is opt-in declared deliverables

In project-open-managed-agents, output_file is not a default-on write to /mnt/session/outputs/. It is an opt-in tool (same configs gate as browser / run_dynamic_worker) that marks a file as a session deliverable.

Enable via agent toolset config, e.g. agent_toolset_20260401 with { "name": "output_file", "enabled": true }. Declared files emit agent.output_declared into the session event log and surface in the Console Artifacts tab.

Marketing copy on https://oma.duyet.net names this under Building Blocks → Artifacts.

Why: Operators want intentional keep-this artifacts, not every sandbox write. How to apply: Do not assume output_file is always present; check agent configs. Full Artifacts panel listing is a separate slice.