fix(precompile-storage): clear stale dynamic tail chunks 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]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[github-actions]

install_with_observer hardcodes StorageSemantics::Legacy, unlike the other precompiles (B20Factory, PolicyRegistryPrecompile, BerylLookup) which derive semantics from the upgrade parameter. If a caller uses ActivationRegistry::install_with_observer directly at Cobalt, they'd silently get Legacy semantics.

This is safe today because the central BasePrecompiles::install_with_observer always passes the correct semantics, but consider adding an upgrade parameter (or at least a doc comment warning that this always uses Legacy) to keep the API consistent and prevent future misuse.

[arjun-dureja]

Addressed in 044530b. Activation Registry convenience paths now derive StorageSemantics::Legacy vs StorageSemantics::Cobalt from ActivationAdminConfig::state_enabled, including install_with_config, install_with_observer, and precompile_with_observer. Added a focused test covering static-fallback and state-backed configurations.