# K1566–K1570: per-handle offset and seek

Each successful read-only open owns an independent cursor. A read completion advances only that handle's offset by the actual returned byte count, which must not exceed the requested count. Zero-byte and short completions preserve the untransferred portion. A successful seek publishes the new offset atomically.

`Start`, `Current`, and `End` seek bases use signed 128-bit arithmetic before narrowing to a 64-bit offset. Negative and overflowing results fail without changing either cursor. An invalid completion or unknown handle likewise leaves the table unchanged. The positive case performs a short read followed by two seeks while the other handle stays at zero. The negative case injects negative and overflowing seeks, then demonstrates that the other handle still progresses.

This is a bounded two-handle in-memory model. Disk-backed reads and a userspace seek ABI remain separate work; product release acceptance is still open.