feat(protocol): add gateway transport authority contracts

frames/datagram-v1.md

@@ -1,7 +1,9 @@
 # VerseVDI control datagram v1
 
-Phase 3A reserves a bounded control-datagram envelope. It does not forward video,
-audio, provider traffic, VM traffic, or arbitrary binary clipboard data.
+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:
 
@@ -22,6 +24,9 @@ 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 Phase 3A channels are `control.ack.v1`, `control.cancel.v1`, and
-`clipboard.text.v1`. Clipboard payloads are UTF-8 JSON text contracts and remain
-subject to the 65,536-byte text limit and explicit authorization.
+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
+authorization.