Storylines: the same site told several ways, one per visitor, counted

Any text a person reads may be a list, one entry per storyline, every
list the same length. A visitor is given one storyline for the whole
site and reads it on every page and in every mail about their case.
Records and events carry the storyline; GET /report gives counts per
bucket, storyline and state, and nothing else.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GT37Z1Xtfd9pUuQtMTg6Yt

docs/README.md

@@ -11,6 +11,7 @@ engine does with it.
 | [Content reference](content-reference.md) | Every key a content repo may write, and what it does. |
 | [State machines](state-machines.md) | `aggregates.yaml`: stages, who moves a case, mail, deadlines, memberships. |
 | [Access](access.md) | How the Cedar policy is compiled from content, and who may ask it what. |
+| [Storylines](storylines.md) | The same site told several ways: lists of texts, one storyline per visitor, counted per storyline. |
 | [Memberships](memberships.md) | Groups kept by portal itself: a membership as a case, a person as a phone number first, and the provider only saying who. |
 | [Operations](operations.md) | Releasing, deploying, adding a site, environment variables. |
 | [Filesystem routes](design/filesystem-routes.md) | Why the `questions/` tree is the router. |