practice fix — creation is graph-domain: cluster picker, nodeIds-only API (owner ruling 2026-09-29)

Owner ruling: 'problem sets always take in nodes — graph objects' —
practice is graph-domain, not chat-domain. No session-created sets.

API: POST /api/practice/sets takes {nodeIds, params, title?} ONLY —
the chatId branch, UnknownChatError, and the any-provenance filter are
deleted; the selector is nodeIds (readNodes filtered to the selection,
unknown ids drop, empty live intersection → 400 empty_selection);
title optional from the UI (the picker's cluster label), dated default
stays. chatStore leaves the pipeline deps entirely (labels resolve
store-side in the clusters service).

GET /api/graph/clusters (new): the birth-session groups the graph view
renders — graphSnapshot's clusters verbatim (same ordering, same
MIN_CLUSTER_SIZE presentation filter), mapped to {key, kind
chat|notes, label (null when the naming record is gone — honest,
never guessed), nodeIds, nodeCount}; corrupt/empty graph → empty
list. GraphClusterGroup contract in core/contracts/graph.ts (client-
safe — the dialog imports it).

practice-dialog: session picker → cluster picker (rows show label +
proposition count, notes clusters marked); Create posts the cluster's
nodeIds + label as title + params. 400 empty-selection copy reworded
for the vanished-nodes edge ('Nothing practicable is left in that
cluster — the graph changed.'); 503 deep link unchanged. Preselected
mode gone — the dialog is the only creation entry for now (the graph-
view cluster entry comes later with free-form selection).

Sidebar: session right-click 'Practice this session's propositions'
removed (item + state + dialog wiring); the /practice nav row stays.

Tests: pipeline — chatId/any-provenance tests die, nodeIds selection
pins added (unknown-id filtering, dated-default title, title hint
rides, empty/vanished → EmptySelectionError); render — cluster picker
pins (label+count rows, notes kind, unlabeled cluster muted, empty
graph line), preselected pins removed; 16 render + 13 pipeline.

Docs: architecture.md §7 API+UI paragraph rewritten (graph-domain
ruling, /api/graph/clusters, cluster picker as the only entry, no
404-unknown-chat); README creation-flow line updated.

1130/1130, tsc 0, lint 0, build 0.

docs/architecture.md

@@ -380,7 +380,7 @@ Practice turns the graph into problem sets the learner reasons through out loud.
 
 **The jobs pattern — registry, not JobRecords.** Practice runs are NOT Workbench jobs: no `JobStore` records, no steer messages, nothing ever wakes the teacher — a practice run isn't chat-scoped (a set outlives its birth session and has no lesson to re-enter; its result is itself, persisted in its own store and read by its own page). What it shares with the Workbench is the observability surface: a `globalThis` run registry (the module-instance idiom — `__lhPracticeRuns`), one row per set-phase (`setId:generation`, `setId:grading`), feeding the activity dock (GraduationCap rows; abort is set-scoped and idempotent; a boot sweep marks orphaned `partitioning`/`generating` sets as `error "Interrupted (server restarted)"` — the job runner's crash-honesty at set grain). Store writes serialize behind a per-set mutex; the pipeline is the sole writer of `data/practice`.
 
-**API + UI.** `POST /api/practice/sets` (create — `{chatId, params}` or `{nodeIds, params}`; 202 `{id}`, generation fire-and-forget; 400 empty selection/bad params, 404 unknown chat, 503 model/key refusal) · `GET /api/practice/sets` · `GET/DELETE /api/practice/sets/[id]` (delete aborts live runs first) · `POST /api/practice/sets/[id]/answers` (202; 409 when not ready). Surfaces: `/practice` (the list — status/counts rows, delete confirm, the new-set dialog with the three dials and a session picker) and `/practice/[id]` (the exam page — numbered problems, markdown statements with math healing at the display seam, a textarea + focus-gated dictation bar per problem, one Submit per set, the post-grade reveal). Entries: the sidebar's Practice nav row and the session right-click "Practice this session's propositions".
+**API + UI.** Creation is GRAPH-DOMAIN, not chat-domain (owner ruling 2026-09-29: "problem sets always take in nodes — graph objects"): `POST /api/practice/sets` takes `{nodeIds, params, title?}` ONLY — no chatId, no clusterId; the UI resolves a picked cluster to its member node ids and passes the cluster's label as the title. `GET /api/graph/clusters` serves the picker: the birth-session clusters the graph view renders (`graphSnapshot`'s clusters verbatim — same ordering, same MIN_CLUSTER_SIZE presentation filter), each as `{key, kind: "chat"|"notes", label, nodeIds, nodeCount}`; a cluster whose naming record is gone keeps `label: null` — honest, never guessed. 202 `{id}` with generation fire-and-forget; 400 empty selection (empty intersection with live nodes — the vanished-nodes edge) / bad params; 503 model/key refusal. `GET /api/practice/sets` · `GET/DELETE /api/practice/sets/[id]` (delete aborts live runs first) · `POST /api/practice/sets/[id]/answers` (202; 409 when not ready). Surfaces: `/practice` (the list — status/counts rows, delete confirm, the new-set dialog with the three dials and the cluster picker — the ONLY creation entry for now; the graph-view cluster entry comes later with the free-form selection UI) and `/practice/[id]` (the exam page — numbered problems, markdown statements with math healing at the display seam, a textarea + focus-gated dictation bar per problem, one Submit per set, the post-grade reveal). Entry: the sidebar's Practice nav row.
 
 **Model wiring.** Three roles — `partitioner`, `problemGenerator`, `grader` — all pinned to the **strong** slot (quality-critical, one settings edit from cheap) and in `BACKGROUND_MODEL_ROLES` (per-role overrides). The stage agents are single-submit loops on the shared `runSubmitAgent` seam (`submit-agent.ts`, extracted from extraction for exactly this): a `validate` hook turns a bad submit into a tool-input error the model retries against, within `maxTurns 4`; exhaustion fails the stage honestly (the set says so, the chains re-run cleanly on a new set).