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.

src/server/graph.ts

@@ -1,6 +1,6 @@
 import * as fs from "node:fs";
 import { LEDGER_FILES, POSITIONS_FILE } from "../../config.ts";
-import type { GraphSnapshot } from "../core/contracts.ts";
+import type { GraphClusterGroup, GraphSnapshot } from "../core/contracts.ts";
 import type { GraphCostSummary } from "../core/cost-summary.ts";
 import { graphCostSummary } from "../core/cost-summary.ts";
 import { graphSnapshot } from "../core/graph.ts";
@@ -23,6 +23,24 @@ export function graphView(): GraphSnapshot {
 	return graphSnapshot(stores);
 }
 
+/** GET /api/graph/clusters — the birth-session groups the graph view
+ *  renders, resolved to node ids for the practice picker (owner ruling
+ *  2026-09-29: cluster→nodeIds resolves in the UI; the API stays
+ *  graph-domain). Reuses the snapshot's clustering verbatim — same
+ *  ordering (size desc, ties by id) and the same MIN_CLUSTER_SIZE
+ *  presentation filter the canvas honors. A corrupt/empty graph is an
+ *  empty list. */
+export function graphClusters(): GraphClusterGroup[] {
+	const snap = graphSnapshot(stores);
+	return snap.clusters.map((cluster) => ({
+		key: cluster.id,
+		kind: cluster.id in snap.sessions ? "chat" : "notes",
+		label: cluster.label,
+		nodeIds: cluster.members,
+		nodeCount: cluster.members.length,
+	}));
+}
+
 /** The graph view's cost surface (GET /api/graph/costs — the 2026-09 cost
  *  pill): fold every usage channel into stage totals + recent runs. A pure
  *  read over the chat records (chat-front-door runs), the notes sources