@@ -54,6 +54,40 @@ function historyFilePath(storagePath: string, taskId: string): string {
 	return path.join(storagePath, "tasks", taskId, GlobalFileNames.historyItem)
 }
 
+// The delete locks the file it unlinks, and the spelling of that path is whatever the
+// store was given: `delete` hands `deleteJsonFile` a joined path, `deleteJsonFile` hands it
+// to `withFileLock`, and `withFileLock` only `path.resolve`s it -- the canonicalisation
+// through fs/promises realpath happens deeper, when the lock file itself is placed, so it
+// never reaches this spy. On the Windows runner the two spellings of one temp file differ
+// (C:/Users/runneradmin/... and its NTFS 8.3 alias C:/Users/RUNNER~1/...), so comparing the
+// key by text holds on a developer box and misses there. File identity is the comparison
+// that holds on both spellings, which is how the landed
+// src/utils/__tests__/safeWriteJson.interruption.test.ts handles the same hazard.
+async function fileIdentity(candidate: string): Promise<string | null> {
+	try {
+		const stats = await actualFs.stat(candidate)
+		return `${stats.dev}:${stats.ino}`
+	} catch {
+		return null
+	}
+}
+
+async function lockKeyNamesTheSameFile(lockKey: unknown, expectedPath: string): Promise<boolean> {
+	if (typeof lockKey !== "string") {
+		return false
+	}
+	// The unlink removes the file and leaves the per-task directory in place, so both sides
+	// still carry an identity here. Case is folded because it is not significant on Windows,
+	// where the alias spelling appears.
+	const expectedDirectory = await fileIdentity(path.dirname(expectedPath))
+	const keyDirectory = await fileIdentity(path.dirname(lockKey))
+	return (
+		expectedDirectory !== null &&
+		keyDirectory === expectedDirectory &&
+		path.basename(lockKey).toLowerCase() === path.basename(expectedPath).toLowerCase()
+	)
+}
+
 function storeInternals(store: TaskHistoryStore): {
 	cache: Map<string, HistoryItem>
 	taskFileMtimes: Map<string, number>
@@ -152,14 +186,23 @@ describe("TaskHistoryStore best-effort deletion semantics", () => {
 			const store = createStore()
 			await store.initialize()
 			await store.upsert(makeHistoryItem({ id: "locked-delete" }))
+			// The lock spy is created once for the whole file, so clear it to make the
+			// assertion below about this delete and not about every case before it.
+			vi.mocked(withFileLock).mockClear()
 			onWrite.mockClear()
 
 			await expect(store.delete("locked-delete")).resolves.toBeUndefined()
 
-			expect(vi.mocked(withFileLock)).toHaveBeenCalledWith(
-				historyFilePath(storagePath, "locked-delete"),
-				expect.any(Function),
+			const lockCalls = vi.mocked(withFileLock).mock.calls
+			expect(lockCalls).toHaveLength(1)
+			// The lock is taken for the file the delete unlinked, under a function body: the key
+			// is pinned by identity rather than by text, and the arity and the body are pinned
+			// alongside it so an argument dropped or swapped cannot slip through.
+			expect(lockCalls[0]).toHaveLength(2)
+			expect(await lockKeyNamesTheSameFile(lockCalls[0][0], historyFilePath(storagePath, "locked-delete"))).toBe(
+				true,
 			)
+			expect(lockCalls[0][1]).toBeTypeOf("function")
 			await expect(fs.access(historyFilePath(storagePath, "locked-delete"))).rejects.toMatchObject({
 				code: "ENOENT",
 			})
 
@@ -0,0 +1,51 @@
+import * as fs from "fs/promises"
+import * as os from "os"
+import * as path from "path"
+
+import { safeWriteText } from "../safeWriteText"
+
+// No fs mocks in this file: the point is to assert what a real filesystem ends up
+// holding after a publish attempt, which the mocked spec cannot show. The failure is
+// provoked with real filesystem semantics rather than with a stubbed call.
+describe("safeWriteText against a real filesystem", () => {
+	let dir: string
+
+	beforeEach(async () => {
+		dir = await fs.mkdtemp(path.join(os.tmpdir(), "safe-write-text-int-"))
+	})
+
+	afterEach(async () => {
+		await fs.rm(dir, { recursive: true, force: true })
+	})
+
+	it("publishes the new bytes and leaves no staging or backup residue", async () => {
+		const targetPath = path.join(dir, "target.txt")
+		await fs.writeFile(targetPath, "old bytes")
+
+		// No platform override: the real platform's own durability and ACL steps run.
+		// A failed icacls restore in a throwaway temp directory is reported, not thrown,
+		// so the publish still lands.
+		await safeWriteText(targetPath, "new bytes", { backup: true })
+
+		expect(await fs.readFile(targetPath, "utf8")).toBe("new bytes")
+		expect(await fs.readdir(dir)).toEqual(["target.txt"])
+	})
+
+	it("leaves the target bytes untouched when the commit cannot replace it", async () => {
+		// A regular file cannot be renamed over a directory, so the commit rename itself fails on a
+		// real filesystem with no mocking at all. No backup is asked for: with backup:true the run
+		// stopped one step earlier, at the backup copy hitting the same EISDIR, and the commit rename
+		// this test is named for never ran.
+		const targetPath = path.join(dir, "target-dir")
+		await fs.mkdir(targetPath)
+		const inside = path.join(targetPath, "payload.txt")
+		await fs.writeFile(inside, "original bytes")
+
+		await expect(safeWriteText(targetPath, "new data")).rejects.toThrow()
+
+		// The directory and its content are exactly as they were, and no backup copy
+		// or staging directory was left behind next to them.
+		expect(await fs.readFile(inside, "utf8")).toBe("original bytes")
+		expect(await fs.readdir(dir)).toEqual(["target-dir"])
+	})
+})