File content: string for text, Uint8Array for binary. Undefined on failure.
1-indexed last source line represented by content.
Error message on failure, undefined on success
MIME type of the file, when available
0-indexed offset of the next unread source line. Omitted when the returned text reaches EOF.
1-indexed first source line represented by content.
Text pagination fields are optional so older/custom backends remain valid.
Total number of logical source lines for a text read, when known. Omitted for binary reads and for backends that cannot determine it.
Structured result from backend read operations.
Replaces the previous plain string return, giving callers a programmatic way to distinguish errors from content.
