fix(checkpoint): flush captured members through update handles on Windows

On native Windows every runtime.checkpoint_artifacts capture and materialize
aborts with EPERM -4048 fsync: copyComponent flushes each copied member
through a read-only handle (open(destination, "r") + sync()), and Windows
FlushFileBuffers requires update access. loopx-project#6415 made the flush read-only so an
ordinary non-root POSIX controller can capture a read-only participant's
0o444 copy, and the flush itself is deliberate (loopx-project#6258). Keep the flush on
every platform: open the staged copy for update, and when the copy is
read-only (POSIX 0o444 mode or the Windows read-only attribute) grant owner
access only for the sync, then restore the reviewed mode before the copy is
witnessed or published. The checkpoint artifact suite gains a read-only
participant case and the established Windows symlink host-privilege guard;
14 of 14 tests pass on native Windows (was 5 of 13).

Signed-off-by: JasonBuildAI <jasonbuildai@gmail.com>

Author: JasonBuildAI

loopx/control_plane/runtime/checkpoint_artifacts.ts

@@ -4,7 +4,7 @@
  */
 import {createHash} from "node:crypto";
 import {createReadStream} from "node:fs";
-import {copyFile, lstat, mkdir, mkdtemp, open, readFile, readdir, rm} from "node:fs/promises";
+import {chmod, copyFile, lstat, mkdir, mkdtemp, open, readFile, readdir, rm} from "node:fs/promises";
 import {dirname, isAbsolute, join, resolve, sep} from "node:path";
 import type {JsonObject} from "../effect_program.ts";
 import {jsonObject, requireJsonObject, requireNonEmptyString} from "../runtime_decode.ts";
@@ -114,6 +114,28 @@ async function sqliteSidecar(path: string, suffixes: string[]): Promise<boolean>
   try {return (await lstat(database)).isFile() && await sqliteFile(database);}
   catch (error) {if ((error as NodeJS.ErrnoException).code === "ENOENT") return false; throw error;}
 }
+async function syncCopiedFile(path: string): Promise<void> {
+  const handle = await open(path, "r+");
+  try {await handle.sync();} finally {await handle.close();}
+}
+/** Flush a freshly copied checkpoint member through an updatable handle.
+ * copyFile preserves a read-only participant's mode, and Windows
+ * FlushFileBuffers rejects read-only handles, so a read-only copy grants owner
+ * access only to this staged copy for the durability sync and restores its
+ * mode before the caller witnesses or publishes it. POSIX syncs a read-only
+ * handle directly, but the update path covers both read-only cases.
+ */
+async function flushCopiedFile(path: string): Promise<void> {
+  try {await syncCopiedFile(path);}
+  catch (error) {
+    const code = (error as NodeJS.ErrnoException).code;
+    if (code !== "EACCES" && code !== "EPERM") throw error;
+    const mode = (await lstat(path)).mode & 0o777;
+    await chmod(path, mode | 0o600);
+    try {await syncCopiedFile(path);}
+    finally {await chmod(path, mode);}
+  }
+}
 async function copyComponent(source: string, destination: string, snapshotDatabases = true): Promise<void> {
   const stat = await lstat(source);
   if (stat.isSymbolicLink()) throw new Error("checkpoint source became a symlink");
@@ -135,10 +157,7 @@ async function copyComponent(source: string, destination: string, snapshotDataba
     // SQLite's existing physical snapshot owner seals committed WAL contents.
     if (snapshotDatabases && await sqliteFile(source)) await snapshotSqliteDatabase(source, destination);
     else await copyFile(source, destination);
-    // copyFile preserves a read-only participant's mode. Syncing its bytes
-    // needs no write access; r+ fails for an ordinary non-root controller.
-    const handle = await open(destination, "r");
-    try {await handle.sync();} finally {await handle.close();}
+    await flushCopiedFile(destination);
   } else throw new Error("checkpoint source contains an unsupported file type");
 }
 function manifestBody(raw: unknown): JsonObject {

tests/control_plane_ts/checkpoint_artifacts.test.ts

@@ -1,6 +1,6 @@
 import assert from "node:assert/strict";
 import test from "node:test";
-import {chmod, mkdir, mkdtemp, readFile, readdir, realpath, rm, symlink, writeFile} from "node:fs/promises";
+import {chmod, mkdir, mkdtemp, readFile, readdir, realpath, rm, stat, symlink, writeFile} from "node:fs/promises";
 import {tmpdir} from "node:os";
 import {join} from "node:path";
 import {checkpointArtifacts} from "../../loopx/control_plane/runtime/checkpoint_artifacts.ts";
@@ -39,6 +39,22 @@ test("capture, verify and inert materialization preserve executable code and emp
     expected_sha256: captured.sha256, destination: join(root, "restored")}), /already exists/);
 });
 
+test("a read-only participant's copied mode survives the durability flush and materialization", async t => {
+  const {root, request} = await fixture(t);
+  await chmod(join(root, "code/solution.sh"), 0o444);
+  const components = request.components;
+  const probe = await checkpointArtifacts({action: "probe", components});
+  const captured = await checkpointArtifacts({...request, components, expected_source_sha256: probe.source_sha256});
+  assert.equal(captured.integrity_verified, true);
+  const copied = join(root, "captured/components/code/solution.sh");
+  assert.equal((await stat(copied)).mode & 0o777, 0o444);
+  await checkpointArtifacts({action: "materialize", root: request.destination, expected_sha256: captured.sha256,
+    destination: join(root, "restored")});
+  const restored = join(root, "restored/components/code/solution.sh");
+  assert.equal(await readFile(restored, "utf8"), "#!/bin/sh\nexit 0\n");
+  assert.equal((await stat(restored)).mode & 0o777, 0o444);
+});
+
 test("changed source, duplicate identities and overlapping sources publish no unit", async t => {
   const {root, request} = await fixture(t);
   await writeFile(join(root, "conversation"), "new native cursor");
@@ -90,8 +106,12 @@ test("symlink sources, nested links and redirected destinations reject without p
   const {root, request} = await fixture(t);
   await symlink(join(root, "code"), join(root, "alias"), process.platform === "win32" ? "junction" : "dir");
   await assert.rejects(checkpointArtifacts({action: "probe", components: [{id: "code", source_path: join(root, "alias")}]}), /symlink/);
-  await symlink(join(root, "conversation"), join(root, "code/link"));
-  await assert.rejects(checkpointArtifacts(request), /symlink/);
+  // File symlink creation needs Developer Mode or admin on Windows; the
+  // junction cases still cover redirected sources and destinations.
+  if (process.platform !== "win32") {
+    await symlink(join(root, "conversation"), join(root, "code/link"));
+    await assert.rejects(checkpointArtifacts(request), /symlink/);
+  }
   await assert.rejects(checkpointArtifacts({...request, destination: join(root, "alias/capture")}), /symlink/);
 });