Phase 15: call ensureCompactionSourceMarked on session_compact

Safety net when session_before_compact does not run so auto compaction
still sets lastCompactionSource and passes the reinject gate.

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

src/index.ts

@@ -11,6 +11,7 @@ import { registerSkillReinjectCommand, updateSkillReinjectStatusLine } from "./c
 import {
 	consumeCompactionOnSessionCompact,
 	createCompactionRuntime,
+	ensureCompactionSourceMarked,
 	markAutoCompactionBeforeCompact,
 	markManualCompactionFromInput,
 } from "./compaction.js";
@@ -103,6 +104,7 @@ export default function skillReinject(pi: ExtensionAPI): void {
 		const trackedNames = state.skills.map((skill) => skill.name);
 		const keptEntries = getKeptEntries(branch, event.compactionEntry.firstKeptEntryId);
 		const keptPresent = skillsPresentInKeptWindow(keptEntries, trackedNames);
+		ensureCompactionSourceMarked(compactionRuntime);
 		const shouldReinject = consumeCompactionOnSessionCompact(
 			compactionRuntime,
 			state,