Function resolveUniqueBackupFileName

resolveUniqueBackupFileName(
    fileName: string,
    existingFileNames: Iterable<string>,
    options?: { caseInsensitive?: boolean },
): string
Picks the first available backup filename in a Windows-style duplicate series. When sermon.mp4 already exists, returns sermon (1).mp4, then sermon (2).mp4, and so on.
Parameters
- fileName: string
  Desired backup filename, including extension.
- existingFileNames: Iterable<string>
  Filenames already present in the target remote directory.
- Optionaloptions: { caseInsensitive?: boolean }
  Matching options for remote filesystem semantics.
  - OptionalcaseInsensitive?: boolean
    When true, treats names as equal regardless of case (SMB).
Returns string
A filename that does not collide with existingFileNames under the chosen rules.

Throws
When every slot from the base name through MAX_BACKUP_FILE_COPY_SUFFIX is already occupied (not expected in practice).
- Defined in lib/backup-filename.ts:492