fix(server): tolerate the missing directory fsync on Windows#9569

Note

Low Risk Narrow platform-specific errno handling around fsync; Unix behavior is unchanged except opening temp files as read-write for sync.

Overview Fixes durable writes on Windows for boot-service install files and service-launcher state/backup paths that atomically rename temp files then fsync the parent directory.

Temp-file flushes now open handles with r+ instead of read-only, because Windows refuses to sync without write access. Directory fsync still runs on Unix for crash safety, but EPERM is ignored on Windows where directory sync is unsupported and NTFS is expected to journal the rename.

In serviceLauncher.ts, directory sync is centralized in syncDirectory (with the same EPERM rule) and writeServiceState calls that helper instead of inlining directory sync.

^{Reviewed by Cursor Bugbot for commit 4c642ebd4f8cd9ef61e2fc03210ea536506be7ac. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Tolerate missing directory fsync on Windows in bootService file writer

The durable file-writing path in bootService.ts previously failed on Windows because the platform does not support directory fsync. The temp-file flush handle is now opened in read-write mode, and directory sync errors are ignored only when they return EPERM, while other errors still propagate. This lets the write complete on Windows without weakening error handling elsewhere.

^{Macroscope summarized 4c642eb.}