When store_media_file returns a data URI (non-CoPilot graph executions
without workspace_id), the result was silently discarded. Binary files
would lose their content, keeping only a "[Binary file: N bytes]"
placeholder. Now the data URI is stored in content_str on the success
path too, not just in the except fallback.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>