# VerseVDI control datagram v1

Phase 3C adds bounded encoded video/audio and sequenced-input channels to the same
transport envelope. The gateway forwards encoded bytes; it does not decode, encode,
transcode, render, or expose provider traffic. Arbitrary binary clipboard data remains
rejected.

All multi-byte integers are unsigned big-endian. The fixed header is 21 bytes:

| Offset | Size | Field | Rule |
|---:|---:|---|---|
| 0 | 2 | magic | ASCII `VD` (`0x56 0x44`) |
| 2 | 1 | version | `1` only |
| 3 | 1 | channel | registered channel identifier |
| 4 | 1 | flags | registry-defined; unknown bits reject |
| 5 | 4 | sequence | session-local wrapping sequence |
| 9 | 8 | timestamp_ms | sender timestamp, bounded by transport skew policy |
| 17 | 1 | fragment_index | zero-based; `0` when not fragmented |
| 18 | 1 | fragment_count | `1` when not fragmented; index less than count |
| 19 | 2 | payload_length | exact payload byte count |

The complete frame is at most 65,536 bytes and `payload_length` is at most 65,515.
Truncated, oversized, unknown-version, unknown-channel, invalid-fragment, and
length-mismatch frames are rejected before allocation proportional to the claimed
payload. Media/provider identifiers are not registered channels.

Registered channels are `control.ack.v1`, `control.cancel.v1`, `clipboard.text.v1`,
`media.video.v1`, `media.audio.v1`, and `input.sequenced.v1`. Media/input frames use
application flow IDs 10, 11, and 12 and a path-MTU-safe payload limit of 1,179 bytes;
larger encoded units use at most 16 validated fragments. Clipboard payloads are UTF-8
JSON text contracts and remain subject to the 65,536-byte text limit and explicit
Server-owned direction, rate, and loop-token policy as defined in
`gateway-clipboard-v1.md`.

Within an active Phase 3C gateway session, `input.sequenced.v1` and the
bidirectional reliable `control.ack.v1` payloads additionally use the exact
provider-neutral grammars in [gateway-input-feedback-v1.md](gateway-input-feedback-v1.md).
Those grammars do not alter this datagram header or make provider traffic visible to
the Verse client.