fix(task-history): atomic read-modify-write

  prevents cross-process lost updates

Author: edelauna

src/core/task-persistence/TaskHistoryStore.ts

@@ -915,18 +915,16 @@ export class TaskHistoryStore {
 
 		await safeWriteJson(indexPath, index, {
 			merge: (existing, incoming) => {
-				if (!existing || existing.version !== 1 || !Array.isArray(existing.entries)) {
-					return incoming
+				const prev = existing as HistoryIndex | null
+				const next = incoming as HistoryIndex
+				if (!prev || prev.version !== 1 || !Array.isArray(prev.entries)) {
+					return next
 				}
-				const ourIds = new Set(incoming.entries.map((e: HistoryItem) => e.id))
-				const peerEntries = existing.entries.filter(
-					(e: HistoryItem) => e.id && !ourIds.has(e.id) && onDiskIds.has(e.id),
-				)
+				const ourIds = new Set(next.entries.map((e) => e.id))
+				const peerEntries = prev.entries.filter((e) => e.id && !ourIds.has(e.id) && onDiskIds.has(e.id))
 				return {
-					...incoming,
-					entries: [...incoming.entries, ...peerEntries].sort(
-						(a: HistoryItem, b: HistoryItem) => b.ts - a.ts,
-					),
+					...next,
+					entries: [...next.entries, ...peerEntries].sort((a, b) => b.ts - a.ts),
 				}
 			},
 		})

src/utils/__tests__/safeWriteJson.test.ts

@@ -476,7 +476,10 @@ describe("safeWriteJson", () => {
 
 		const incoming = { b: 3, c: 4 }
 		await safeWriteJson(currentTestFilePath, incoming, {
-			merge: (existing, data) => ({ ...existing, ...data }),
+			merge: (existing, data) => ({
+				...(existing as Record<string, unknown>),
+				...(data as Record<string, unknown>),
+			}),
 		})
 
 		const content = await readFileContent(currentTestFilePath)