protocol: add canonical Phase 3A contract sources

frames/datagram-v1.md

@@ -0,0 +1,27 @@
+# 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.
+
+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 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.