Summary

Add benchmarked weight infrastructure, UTXO count validation, and actual-weight correction to the process_tokens inherent extrinsic, enabling accurate block weight accounting for the cnight-observation pallet.

🎫 Ticket 📐 Engineering

Motivation

The process_tokens inherent extrinsic previously declared zero weight with DispatchClass::Mandatory, bypassing block weight accounting entirely. Least Authority audit finding Issue H flagged this: without benchmarked weights, the runtime cannot accurately track block capacity consumed by UTXO processing, and there is no upper bound on UTXO batch size.

This implementation adds the FRAME benchmarking infrastructure needed to derive accurate weights, a runtime safety guard on input size, and actual-weight correction via PostDispatchInfo so that block capacity reflects the true processing cost.

Changes

• WeightInfo trait (weights.rs) — New WeightInfo trait with fn process_tokens(n: u32) -> Weight, placeholder SubstrateWeight<T> implementation with conservative estimates, and zero-weight () impl for tests
• Weight annotation (lib.rs) — process_tokens weight changed from (0, DispatchClass::Mandatory) to (T::WeightInfo::process_tokens(MAX_UTXO_COUNT), DispatchClass::Mandatory) declaring worst-case weight up front
• UTXO count guard (lib.rs) — New TooManyUtxos error variant; ensure! guard rejects batches exceeding CardanoTxCapacityPerBlock * UTXO_PER_TX_OVERESTIMATE (default 200 × 64 = 12,800)
• Actual-weight correction (lib.rs) — Return type changed from DispatchResult to DispatchResultWithPostInfo; returns PostDispatchInfo { actual_weight: Some(T::WeightInfo::process_tokens(utxo_count)), pays_fee: Pays::No }
• Pallet constants (lib.rs) — UTXO_PER_TX_OVERESTIMATE = 64, MAX_UTXO_COUNT = 12,800
• Benchmark (benchmarking.rs) — FRAME v2 parameterized benchmark using Registration UTXOs with Linear<0, MAX_UTXO_COUNT>
• Config updates — type WeightInfo: WeightInfo added to pallet Config trait; wired as () in mock runtimes and runtime
• Runtime registration — Pallet registered in define_benchmarks! macro
• Validation tests (validation_tests.rs) — 3 tests using lightweight mock: UTXO guard rejection (TC-01), exact boundary acceptance (TC-02), PostDispatchInfo actual-weight verification (TC-06b)

📌 Submission Checklist

• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason: included
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• No new todos introduced

🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other
• N/A

🗹 TODO before merging

• Ready for review
• Run benchmarks on target hardware to generate production weights (post-merge deployment step)