Discovery-drill prompt-template versioning. Each discovery_prompt_generated event must reference the exact prompt template version used (hash or version_id), so audits can reconstruct WHY a drill unfolded the way it did, not just WHAT the output was. The prompt template is a mutable artifact (file or substrate row); without versioning, a future template change would silently produce wildly different drill behavior with no audit trail of the input. Surfaced by Deepseek in synthesis-validation poll b82e9fff as a NEW hidden obligation that emerged from the synthesis itself, not from Round-1 obligations. Deferred to Cycle 2 (Discovery Drill Prompt + Wizard State + Prompt Versioning) where the prompt template work lands. Implementation TBD in Cycle 2: either store template hash on the event row, or add a prompt_templates substrate table with version pointers.