W5: probe/teach phases — divider + collapsed teach checks

components/artifacts/plan-divider.tsx

@@ -1,9 +1,29 @@
-import type { ArtifactPartProps } from "@/src/core/contracts";
+import type { ArtifactPartProps, PlanToolResult } from "@/src/core/contracts";
 
 /**
- * Phase divider rendered where plan_init lands in the transcript (W5).
- * Probe → teach transition marker per vision §2 "Two phases".
+ * The probe→teach divider (vision §2 "Two phases, clearly separated").
+ *
+ * Rendered by the artifact registry wherever the session's plan_init part
+ * sits in the transcript — the plan call IS the transition marker, so the
+ * divider marks the seam: probing above, teaching below. Deliberately quiet:
+ * a hairline rule with a small chip, never a banner.
+ *
+ * Renders null until the tool's output is available AND the init succeeded —
+ * a failed first plan_init must not mark the seam (the retry that succeeds
+ * draws the divider at its own, correct spot).
  */
-export function PlanDivider(_props: ArtifactPartProps) {
-	return null;
+export function PlanDivider({ part }: ArtifactPartProps) {
+	if (part.state !== "output-available") return null;
+	const result = part.output as PlanToolResult | undefined;
+	if (!result || result.ok !== true) return null;
+	const nodeCount = result.tree?.nodes?.length ?? 0;
+	return (
+		<div className="my-4 flex w-full items-center gap-3" data-testid="plan-divider">
+			<span className="h-px flex-1 bg-border/80" />
+			<span className="rounded-full border border-border/80 px-2.5 py-0.5 text-[11px] font-medium uppercase tracking-wide text-muted-foreground">
+				Teaching{nodeCount > 0 ? ` · ${nodeCount} node${nodeCount === 1 ? "" : "s"}` : ""}
+			</span>
+			<span className="h-px flex-1 bg-border/80" />
+		</div>
+	);
 }