Prologue to Book 2

TBD — placeholder. This prologue hasn't been written yet. It will tell how Som came to the arena, sided with the party and escaped with them (2021-10-13 → 2021-12-22), built from the user's recollection and a single, reluctant citation of the druids' record of the arena (Book 1, block E). See "Som's arrival in the arena is unrecorded" and "The prologue waits on Book 1 block E" in story-context.md. The entry exists now so that Book 2's session stories can start with 2022-01-19.