feat: initialize Kurdistan SDK - independent fork of Polkadot SDK

pezkuwi/roadmap/implementers-guide/src/runtime/dmp.md

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+# DMP Pallet
+
+A module responsible for Downward Message Processing (DMP). See [Messaging Overview](../messaging.md) for more details.
+
+## Storage
+
+Storage layout required for implementation of DMP.
+
+```rust
+/// The downward messages addressed for a certain para.
+DownwardMessageQueues: map ParaId => Vec<InboundDownwardMessage>;
+/// A mapping that stores the downward message queue MQC head for each para.
+///
+/// Each link in this chain has a form:
+/// `(prev_head, B, H(M))`, where
+/// - `prev_head`: is the previous head hash or zero if none.
+/// - `B`: is the relay-chain block number in which a message was appended.
+/// - `H(M)`: is the hash of the message being appended.
+DownwardMessageQueueHeads: map ParaId => Hash;
+```
+
+## Initialization
+
+No initialization routine runs for this module.
+
+## Routines
+
+Candidate Acceptance Function:
+
+* `check_processed_downward_messages(P: ParaId, relay_parent_number: BlockNumber, processed_downward_messages: u32)`:
+    1. Checks that `processed_downward_messages` is at least 1 if `DownwardMessageQueues` for `P` is not empty at the
+       given `relay_parent_number`.
+    1. Checks that `DownwardMessageQueues` for `P` is at least `processed_downward_messages` long.
+
+Candidate Enactment:
+
+* `prune_dmq(P: ParaId, processed_downward_messages: u32)`:
+    1. Remove the first `processed_downward_messages` from the `DownwardMessageQueues` of `P`.
+
+Utility routines.
+
+`queue_downward_message(P: ParaId, M: DownwardMessage)`: 1. Check if the size of `M` exceeds the
+    `config.max_downward_message_size`. If so, return an error. 1. Wrap `M` into `InboundDownwardMessage` using the
+    current block number for `sent_at`. 1. Obtain a new MQC link for the resulting `InboundDownwardMessage` and replace
+    `DownwardMessageQueueHeads` for `P` with the resulting hash. 1. Add the resulting `InboundDownwardMessage` into
+    `DownwardMessageQueues` for `P`.
+
+## Session Change
+
+1. For each `P` in `outgoing_paras` (generated by `Paras::on_new_session`):
+    1. Remove all `DownwardMessageQueues` of `P`.
+    1. Remove `DownwardMessageQueueHeads` for `P`.