practice fix follow-up — the picker lists EVERY birth-session group (owner ruling)

Owner escalation on deviation 1: practice availability must not
inherit a visual-rendering threshold. graphClusters() now runs
birthSessionPartition(snap.nodes) directly (same size-desc/id-asc
ordering) instead of reading the snapshot's MIN_CLUSTER_SIZE-filtered
clusters array — MIN_CLUSTER_SIZE stays a hull-drawing rule only.
Label join mirrors the snapshot's (chat title / notes path, null when
the naming record is gone). Contract doc + architecture.md sentence
corrected to match; empty-picker copy reworded ('once a session births
its first proposition' — no 3+ mechanics). Render pins: new empty line
+ a 1- and 2-proposition group listing pin. 1130/1130, tsc 0, lint 0,
build 0.

components/practice-dialog.tsx

@@ -104,7 +104,7 @@ export function PracticeDialogBody({
 					))}
 					{clusters.length === 0 && (
 						<div className="px-3 py-2 text-sm text-muted-foreground">
-							No clusters yet — a cluster appears once a session births 3+ propositions.
+							No clusters yet — a cluster appears once a session births its first proposition.
 						</div>
 					)}
 				</div>