refactor(rpc): type the MMR proof leaf as a fixed 32-byte array

[prajwolrg]

Description

getExportEntryMMRProof took its leaf parameter as Vec<u8>, but the only thing the endpoint can do with a leaf is look it up as a 32-byte entry hash. build_export_entry_mmr_proof did the length check itself and returned InvalidLeafLength for anything else, so the wire type was looser than the code behind it. The practical effect was that a wrong-sized leaf still cost a get_block_height round trip to bitcoind before being rejected.

Typing the parameter as [u8; 32] pushes the check into jsonrpsee's parameter deserialization, ahead of the handler. The signature now says what the builder already enforced, and the error variant is no longer reachable, so it is gone along with the test that covered it.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature/Enhancement (non-breaking change which adds functionality or enhances an existing one)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor
• New or updated tests
• Dependency update
• Security fix

Notes to Reviewers

The JSON wire format does not change. Vec<u8> and [u8; 32] both serialize as an array of 32 numbers, so any well-formed request that worked before still works. What changes for a malformed request is where it fails: a jsonrpsee parameter parse error instead of an application error from the handler.

The generated client signature does change for anyone building this crate with the client feature, since the parameter type is part of it. Nothing in this repo calls it.

Checklist

• I have performed a self-review of my code.
• I have commented my code where necessary.
• I have updated the documentation if needed.
• My changes do not introduce new warnings.
• I have added tests that prove my changes are effective or that my feature works.
• New and existing tests pass with my changes.

The removed test asserted the error the type system now makes unrepresentable, so there is nothing left to test at that layer. The remaining build_export_entry_mmr_proof tests pass unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
bin/asm-runner/src/rpc_server.rs	97.81% <100.00%> (-0.11%)	⬇️

... and 1 file with indirect coverage changes

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[github-actions]

Commit: 8fd2a73
SP1 Execution Results

program	cycles	gas
asm-stf	136,427,562	134,143,979
moho	5,223,688	5,525,436

[github-actions]

🔒 AI Security Review (claude-opus-5)

✅ No security issues found.