SIMD-0297: Relax Invalid Nonced Transactions Constraint

proposals/0297-relax-invalid-nonce.md

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+---
+simd: '0297'
+title: Relax Invalid Nonced Transactions Constraint
+authors: Tao Zhu (Anza)
+category: Standard
+type: Core
+status: Review
+created: 2025-06-05
+feature:
+---
+
+## Summary
+
+This proposal relaxes the handling of invalid durable nonce transactions during
+block replay. Instead of rejecting the entire block when an invalid nonce is
+encountered, the transaction should be marked as failed, skipped for state
+modifications, but still committed to the block without charging a transaction
+fee.
+
+## Motivation
+
+The current consensus behavior specifies that invalid durable nonce transactions
+should result in block failure during replay. This behavior hinders forward
+compatibility with asynchronous block execution. The goal is to align invalid
+nonce handling with the treatment of other soft transaction failures (e.g.,
+relax fee payer, relax ALT, etc).
+
+## New Terminology
+
+None
+
+## Detailed Design
+
+### Current Behavior
+
+A transaction using a durable nonce fails block replay (causing the entire
+block to be rejected) if any of the following occurs:
+
+- The nonce account is not a statically included account.
+- The nonce account does not exist.
+- The nonce account is not properly initialized.
+- The stored nonce does not match the transaction's recent blockhash.
+- The transaction fails to advance the nonce.
+
+
+### Proposed Change
+
+Update replay logic to handle invalid nonce transactions differently:
+
+1. For failure that can be checked without accessing account state, namely:
+
+   - The nonce account is not a statically included account.
+
+Replay logic remains unchanged - entire block is rejected;
+
+2. For failures require account state to verify, namely: 
+
+   - The nonce account does not exist.
+   - The nonce account is not properly initialized.
+   - The stored nonce does not match the transaction's recent blockhash.
+   - The transaction fails to advance the nonce.
+
+Replay treats these transactions as non-state-modifying and non-fee-charging
+failures, as follows:
+
+   - The transaction is not executed.
+   - The transaction is not included in status cache.
+   - The transaction’s non-execution CU cost (i.e., transaction's static CUs,
+     plus actual CUs for loading accounts) still applies to the block limit.
+   - The transaction is recorded in the block (marked as failed).
+   - No account state is modified, including the nonce account (i.e., nonce is
+     not advanced) and fee payer account (it is not charged with the
+     transaction's fee).
+   - The block is not rejected as long as all other transactions replay
+     successfully.
+
+
+## Alternatives Considered
+
+N/A
+
+## Impact
+
+- Invalid nonce transactions may be included in multiple blocks but will not be
+  charged fees.
+
+- The inclusion of the same nonce transaction in multiple blocks may affect RPC
+  behavior, such as querying a transaction by signature. The exact handling of
+  this is outside the scope of this proposal.
+
+## Security Considerations
+
+The relaxed model still prevents nonce reuse and enforces single-use semantics,
+as the transaction does not advance the nonce if it fails. There is no impact
+on replay safety, and the ledger remains consistent across nodes.
+
+## Backward Compatibility
+
+This change is **not backward compatible** with current validator behavior. It
+must be activated via a feature gate and coordinated with a network upgrade.