diff --git a/src/kept.ts b/src/kept.ts
new file mode 100644
index 0000000..ad0a446
--- /dev/null
+++ b/src/kept.ts
@@ -0,0 +1,10 @@
+import type { SessionEntry } from "@earendil-works/pi-coding-agent";
+
+/** Branch slice from firstKeptEntryId through tail (SPEC §6.4). */
+export function getKeptEntries(branch: SessionEntry[], firstKeptEntryId: string): SessionEntry[] {
+	const startIndex = branch.findIndex((entry) => entry.id === firstKeptEntryId);
+	if (startIndex < 0) {
+		return [];
+	}
+	return branch.slice(startIndex);
+}