feat: initialize Kurdistan SDK - independent fork of Polkadot SDK

2025-12-13 15:44:15 +03:00
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+# Bitfield Signing
+
+Validators vote on the availability of a backed candidate by issuing signed bitfields, where each bit corresponds to a
+single candidate. These bitfields can be used to compactly determine which backed candidates are available or not based
+on a 2/3+ quorum.
+
+## Protocol
+
+Input:
+
+There is no dedicated input mechanism for bitfield signing. Instead, Bitfield Signing produces a bitfield representing
+the current state of availability on `StartWork`.
+
+Output:
+
+- `BitfieldDistribution::DistributeBitfield`: distribute a locally signed bitfield
+- `AvailabilityStore::QueryChunk(CandidateHash, validator_index, response_channel)`
+
+## Functionality
+
+Upon receipt of an `ActiveLeavesUpdate`, launch bitfield signing job for each `activated` head referring to a fresh
+leaf. Stop the job for each `deactivated` head.
+
+## Bitfield Signing Job
+
+Localized to a specific relay-parent `r` If not running as a validator, do nothing.
+
+- For each fresh leaf, begin by waiting a fixed period of time so availability distribution has the chance to make
+  candidates available.
+- Determine our validator index `i`, the set of backed candidates pending availability in `r`, and which bit of the
+  bitfield each corresponds to.
+- Start with an empty bitfield. For each bit in the bitfield, if there is a candidate pending availability, query the
+  [Availability Store](../utility/availability-store.md) for whether we have the availability chunk for our validator
+  index. The `OccupiedCore` struct contains the candidate hash so the full candidate does not need to be fetched from
+  runtime.
+- For all chunks we have, set the corresponding bit in the bitfield.
+- Sign the bitfield and dispatch a `BitfieldDistribution::DistributeBitfield` message.