fix(protocol-kit): handle CONTRACT_SIGNATURE in toSafeTransactionType

[indexedfit]

Summary

• Fix toSafeTransactionType in Safe.ts to correctly handle CONTRACT_SIGNATURE confirmations from the Safe Transaction Service
• When signatureType === 'CONTRACT_SIGNATURE', extract the inner signature data from the stored format and create EthSafeSignature with isContractSignature=true
• Without this fix, buildSignatureBytes treats contract signatures as EOA signatures and dumps the full stored blob (header + data) as a flat 65-byte signature, which corrupts the combined signature layout and causes GS021 errors during on-chain execution

Closes #1300

Problem

The Safe Transaction Service stores contract signatures in a specific format:

r(32 bytes) + s(32 bytes) + v(1 byte) + dataLength(32 bytes) + data(N bytes)

When toSafeTransactionType reconstructs a SafeTransaction from TX Service confirmations, it creates EthSafeSignature(owner, signature) for ALL confirmation types — including CONTRACT_SIGNATURE. Since isContractSignature defaults to false, buildSignatureBytes later treats these as EOA signatures and emits the entire stored blob as flat data in the constant part, instead of splitting it into a constant part (with a dynamic offset) and a dynamic part.

This breaks checkNSignatures on-chain when there are multiple signers, because the second signer's 65-byte chunk overlaps with the first signer's oversized blob.

Fix

For CONTRACT_SIGNATURE confirmations:

1. Read the s value (bytes 32–63) from the stored signature to find the offset to the length-prefixed inner data
2. Read the data length at that offset
3. Extract just the inner signature data
4. Create EthSafeSignature(owner, innerData, true) so buildSignatureBytes correctly handles the static/dynamic split

Test plan

• Existing protocol-kit tests pass
• Manual test: execute a multi-signer Safe transaction where one signer is a smart contract (e.g., passkey signer proxy) — the Safe web UI should no longer produce GS021

🤖 Generated with Claude Code

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