Struct TreeClient 

pub struct TreeClient { /* private fields */ }

Client-side sparse vote commitment tree.

Mirrors the server tree via incremental sync. Marks specific positions for witness generation:

• Wallet: marks its own VAN position (for ZKP #2)
• Helper server: marks delegated VC positions (for ZKP #3)

Implementations

impl TreeClient

pub fn empty() -> Self

Create an empty client tree.

pub fn mark_position(&mut self, position: u64)

Register a leaf position for witness generation.

When [sync] encounters this position, the leaf is inserted with Retention::Marked so that [witness] can later produce a Merkle authentication path for it. All other positions are inserted as Retention::Ephemeral (prunable).

Must be called before syncing past the position. This matches the production pattern where the wallet knows its VAN index from MsgDelegateVote before it syncs the block that contains it, and the helper server knows the delegated VC index from the share payload before it syncs.

Calling this for a position that has already been synced has no effect (the leaf is already in the tree as ephemeral).

pub fn sync<A: TreeSyncApi>( &mut self, api: &A, ) -> Result<(), SyncError<A::Error>>

Sync the client tree from a TreeSyncApi source.

Fetches block commitments from the server (incrementally, from the last synced height) and inserts them into the local tree. Each block’s leaves are checkpointed at the block’s height.

Retention: Positions registered via [mark_position] are inserted with Retention::Marked so witnesses can be generated for them. All other positions use Retention::Ephemeral, allowing ShardTree to prune their subtree data once it’s no longer needed. This keeps the client tree sparse — only the subtrees touching marked positions are fully materialized.

Safety checks (these catch corrupted data or protocol mismatches):

• Each block’s start_index must match the client’s expected next position.
• After checkpointing each block, the client’s root is verified against the server’s root at that height (the consistency check described in the README).

pub fn witness(&self, position: u64, anchor_height: u32) -> Option<MerklePath>

Generate a Merkle authentication path for the leaf at position, valid at the given checkpoint anchor_height.

Returns None if the position or checkpoint is invalid, or if the position was not marked.

pub fn root_at_height(&self, height: u32) -> Option<Fp>

Root at a specific checkpoint height (for anchor verification).

After sync, this should match the server’s root at the same height.

pub fn root(&self) -> Fp

Current root (at the latest synced checkpoint).

pub fn size(&self) -> u64

Number of leaves synced.

pub fn last_synced_height(&self) -> Option<u32>

Latest synced block height.