feat(solana-indexer): PR 7.3 decode settlements via the shared interface parser

[squadgazzz]

Description

The settlement decoder hand-rolled the BeginSettle and FinalizeSettle wire layout and stubbed the auction id and the buy-side amounts. It had to: the shared settlement-interface parser needed an on-chain AccountView, which the indexer cannot get off-chain. cowprotocol/solana-programs#80 makes that parser generic over the account type, so the indexer now decodes with its own Pubkey type and drops the duplicated layout and the placeholders.

Changes

• Decode CreateOrder, CreateBuffer, BeginSettle, and FinalizeSettle through the interface parser.
• Fill the real auction id from the parsed BeginSettle (was a placeholder).
• Fill the real buy-side amount from the FinalizeSettle pushes (was a placeholder).
• Read transfer amounts little-endian to match the on-chain encoder (was big-endian).
• Pair pushes to orders positionally, order i is paid by push i, per the on-chain invariant.
• Drop the hand-rolled parse_begin_settle_orders and the account-position constants.

How to test

Updated unit tests.

[squadgazzz]

This will be updated once cowprotocol/solana-programs#80 is merged.

[claude]

Claude finished @squadgazzz's task in 3m 15s —— View job

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PR Review: decode settlements via the shared interface parser

• Read the PR diff and changed files
• Understand the new interface parser integration
• Review decoder.rs changes for correctness
• Review tests
• Post inline comments and summary

This is a clean simplification — dropping the hand-rolled BeginSettle/FinalizeSettle layout and the account-position constants in favor of the now-generic settlement_interface parser is the right move, and it correctly removes the auction-id / buy-amount placeholders. The little-endian fix and the generic Pubkey bridge (to_sdk_pubkey) look right, and the tests were updated to match the real wire.

One substantive point, left as an inline comment:

• Silent zip truncation in decode_settlements_finalized. Pairing orders to pushes by position relies on the "exactly one push per order, same PDA order" invariant (acknowledged in the PR body). But orders.iter().zip(received) silently truncates on a count mismatch, which is inconsistent with the rest of this function's warn-and-skip / untrusted-stream posture. A pushes.len() == orders.len() guard would surface a broken invariant instead of emitting a misaligned settlement.

Nits I did not flag (already acknowledged / fine): the Cargo.toml branch = pin is called out in your own review comment as temporary until solana-programs#80 merges; the auction_id as i64 -> u64 cast is documented as non-negative in practice.

I couldn't compile locally (the settlement-interface git dependency isn't fetchable in this sandbox), so I reviewed the parser integration by reasoning about the diff rather than by building — worth confirming cargo check / the updated unit tests pass in CI.
• solana-indexer/PR7.3-interface-parser

[claude]

zip silently truncates to the shorter of orders / received. This function otherwise warns-and-skips on every layout mismatch (BeginSettle/FinalizeSettle parse failures) and treats the gRPC stream as untrusted (saturating adds), but here a pushes.len() != orders.len() mismatch — i.e. a violation of the "exactly one push per order" invariant this pairing relies on — produces a partial/misaligned trade set with no signal.

Consider guarding it explicitly so a broken invariant surfaces rather than silently corrupting the settlement:

if finalize_input.pushes.len() != begin_input.orders.len() {
    tracing::warn!(
        instruction_index = begin.instruction_index,
        orders = begin_input.orders.len(),
        pushes = finalize_input.pushes.len(),
        "BeginSettle/FinalizeSettle order/push count mismatch, skipping"
    );
    continue;
}

This is also the one place the correctness of amount_received_delta hinges entirely on pushes being 1:1 and in the same PDA order as orders — worth an explicit check now that the resolver is stubbed and the misalignment wouldn't show up in the emitted events yet.