Refresh Gypsum Messaging Stream

Refresh the Gypsum messaging framework context stream.

Optionally pass version_metadata to track training rationale: { "version_metadata": { "Headline": {"content_version_id": "uuid", "change_rationale": "Updated per brand guidelines"}, "Persona: CTO": {"content_version_id": "uuid", "change_rationale": "Refined pain points"} }, "change_source": "training", "change_rationale": "Bulk update after training session" }