fix(precompile-storage): clear stale dynamic tails after Cobalt

[arjun-dureja]

Summary

• clear retired backing slots when shorter Bytes, String, or Vec<T> values overwrite longer values
• preserve legacy storage and gas behavior before Cobalt
• route zero writes through normal SSTORE accounting so EIP-2200/EIP-3529 refunds propagate

Implementation

• add typed StorageSemantics::{Legacy, Cobalt} selected by BasePrecompiles
• thread the selected semantics through direct and dynamically looked-up B-20 precompiles
• clear long bytes/string chunks before writing new metadata
• clear fully retired packed vector slots and recursively delete retired unpacked elements
• preserve handler-based vector pushes so reused pre-Cobalt dynamic slots are cleaned correctly
• reject static writes before preparatory cleanup SLOADs

Scope

This prevents new stale tails at and after Cobalt and cleans legacy tails when their metadata remains reachable. Historical orphaned slots whose old length metadata was already overwritten cannot be discovered without a separate state migration or high-water metadata.

Testing

• cargo +nightly fmt --all -- --check
• cargo test -p base-precompile-storage --all-features
• cargo test -p base-common-precompiles
• cargo test -p base-common-evm
• cargo check -p base-precompile-storage --no-default-features
• RISC0_SKIP_BUILD_KERNELS=1 BASE_SUCCINCT_ELF_STUB=1 cargo clippy -p base-precompile-storage -p base-common-precompiles -p base-common-evm --all-targets -- -D warnings

References

• BOP-339
• Tempo #3840
• Base #3693

[linear]

BOP-339

[cb-heimdall]

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