practice: the learner's creation note — optional free-form input carried to partitioner + generators (owner, 2026-09-29)

- dialog: optional 'Anything else?' textarea (typing-only, 2000-char mirror)
- API: body gains note? — trimmed, whitespace-only omitted, hard 400 over 2000
- pipeline: note persisted on the set and threaded to both agent stages
- agents: THE LEARNER'S NOTE prompt block (present only when set) + the
  weighed-never-owed stance pinned in both doctrines
- fix en route: doubled THE PARAMETERS heading in both prompts since slice 3
  (renderParams owns the heading; the literal blocks removed)

app/api/practice/sets/route.ts

@@ -1,8 +1,9 @@
 /**
  * POST /api/practice/sets — create a problem set (202 {id}; generation
  * runs in the background — the fire-and-forget pipeline). Body:
- *   {chatId, params}          — everything this session touched
- *   {nodeIds, params}         — a manual node selection
+ *   {nodeIds, params, title?, note?}  — a node selection, the cluster's
+ *                                     label, and the learner's optional
+ *                                     free-form note
  * Validation + typed-error mapping live in the service (server/practice).
  * GET — the set list (createdAt desc, the store's order).
  */