Use Safe as eth_call sender for EIP-1271 contract signature validation

[johanneskares]

Motivation

Fixes the root cause behind safe-global/safe-transaction-service#2937.

On-chain, checkSignatures has the Safe itself call isValidSignature on its owner contracts, so msg.sender is always the Safe. The off-chain check in SafeSignatureContract._check_eip1271 performs a from-less eth_call (msg.sender = address(0)), which diverges from the on-chain semantics it is meant to predict.

For most owner contracts this makes no difference, but signatures from msg.sender-dependent owners always fail validation. The canonical example is the SafeWebAuthnSharedSigner from safe-modules (the standard gas-optimized ERC-4337 passkey setup): it stores each Safe's P-256 public key in the Safe's storage and reads it back via ISafe(msg.sender).getStorageAt(...) — in a from-less call there is no configuration to find, so pure-passkey Safes cannot propose transactions or register delegates with the Transaction Service at all.

Change

SafeSignatureContract.is_valid() (sync and async) already receives safe_address — other signature types like SafeSignatureApprovedHash use it — but the contract-signature path ignored it. This PR threads it into the EIP-1271 eth_call as the sender when provided:

• safe_address given → isValidSignature is called with from = safe_address, mirroring on-chain checkSignatures.
• safe_address not given → unchanged from-less call.

Owner contracts that ignore msg.sender (e.g. a Safe validating through its fallback handler) are unaffected.

Tests

Added sync + async tests deploying a minimal EIP-1271 signer that returns the magic value only when msg.sender matches a configured address (emulating the shared signer's behavior), asserting that validation fails without safe_address and succeeds with it. All existing tests in test_safe_signature.py pass (38 passed locally against a local node).

Notes for safe-transaction-service

The service's proposal endpoints already pass safe_address to is_valid, so they gain shared-signer support with a dependency bump and no code change. The delegates v2 endpoint currently passes the delegator as second argument (is_valid(ethereum_client, owner)); supporting shared-signer delegators there needs a small follow-up passing the request's safe — happy to submit that PR as well.

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[johanneskares]

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[johanneskares]

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[johanneskares]

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