Phase 1: add loadStateFromBranch — restore last state entry.

Walk branch backwards for skill-reinject:state custom entries per SPEC §6.3;
return structuredClone of valid v1 snapshot or null for full rescan.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/state.ts

@@ -1,4 +1,4 @@
-import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
+import type { ExtensionAPI, SessionEntry } from "@earendil-works/pi-coding-agent";
 
 /** How a skill was first observed in the session (SPEC §6.2). */
 export type SkillSource = "slash" | "skill-block" | "read";
@@ -39,6 +39,37 @@ export function saveState(pi: ExtensionAPI, state: ExtensionState): void {
 	pi.appendEntry<ExtensionState>(STATE_ENTRY_TYPE, state);
 }
 
+function isExtensionState(data: unknown): data is ExtensionState {
+	if (!data || typeof data !== "object") {
+		return false;
+	}
+	const candidate = data as ExtensionState;
+	return (
+		candidate.version === 1 &&
+		(candidate.sessionOverride === null || typeof candidate.sessionOverride === "boolean") &&
+		Array.isArray(candidate.skills) &&
+		(candidate.lastCompactionSource === null ||
+			candidate.lastCompactionSource === "auto" ||
+			candidate.lastCompactionSource === "manual") &&
+		Array.isArray(candidate.pendingReinject)
+	);
+}
+
+/** Latest persisted state on the branch, or null if none (SPEC §6.3). */
+export function loadStateFromBranch(branch: SessionEntry[]): ExtensionState | null {
+	for (let i = branch.length - 1; i >= 0; i--) {
+		const entry = branch[i];
+		if (entry.type !== "custom" || entry.customType !== STATE_ENTRY_TYPE || entry.data === undefined) {
+			continue;
+		}
+		if (!isExtensionState(entry.data)) {
+			continue;
+		}
+		return structuredClone(entry.data);
+	}
+	return null;
+}
+
 export function createInitialState(): ExtensionState {
 	return {
 		version: 1,