Updates API.md and S3a discovery doc to reflect submitter-details
handling and the draft/submit split.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Carried over from the prior discovery session. Lists the 12 gaps (4 hard
blockers, 8 soft) that S2c closes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>