fix: support USDT and other non-standard ERC20 tokens

[Anand-0037]

Summary

Support ERC-20 tokens such as USDT that do not return a boolean from transferFrom.

• handle optional return values in single and batch payments
• preserve token revert data
• reject false or malformed return values
• add regression coverage for standard and no-return tokens, including batch rollback

Verification

• focused regression tests: 13 passed
• complete contract suite: 41 passed
• Ethereum mainnet-fork USDT smoke tests: 3 passed
• forge build
• git diff --check

The mainnet-fork check used USDT at block 25948877; the RPC-dependent test was kept out of the permanent test suite.

Closes #86

Summary by CodeRabbit

• Bug Fixes

  • Improved invoice payments to support ERC-20 tokens that omit return values or use non-standard response formats.
  • Invalid transfer responses now fail safely, while token-provided revert messages and errors are preserved.
  • Batch payments continue to roll back completely when any transfer fails.

• Tests

  • Added coverage for successful, failed, reverted, and malformed token transfer responses, including validation of non-contract token addresses.

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📥 Commits

Reviewing files that changed from the base of the PR and between e299e8a and 9a49e61.

📒 Files selected for processing (2)

• contracts/src/Chainvoice.sol
• contracts/test/NoReturnERC20.t.sol

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Walkthrough

Chainvoice now handles optional and non-standard ERC-20 transferFrom return data for single and batch invoice payments. Tests cover success, failure, revert bubbling, malformed data, and batch rollback behavior.

Changes

ERC-20 transfer handling

Layer / File(s)	Summary
Safe transfer integration contracts/src/Chainvoice.sol	Adds _safeTransferFrom with assembly-based return-data validation and revert bubbling. payInvoice and payInvoicesBatch use the helper.
Transfer behavior validation contracts/test/NoReturnERC20.t.sol	Adds a configurable ERC-20 mock and tests for no-return, boolean, malformed, reverted, and batch transfer cases. Helper functions validate invoice, balance, fee, and allowance state.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested labels: Solidity Lang

Suggested reviewers: atharva0506

Merge Risk: ⚪ Minimal · up to 9a49e

The updated payment paths support non-standard ERC-20 return values without an active merge-blocking issue.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue #86 requires payments with ERC-20 tokens whose transferFrom returns no value. Chainvoice._safeTransferFrom uses a low-level call, accepts zero-length return data, and is used by both `payInv…
Out of Scope Changes check	✅ Passed	The changes stay within issue #86. The helper, return-data validation, revert bubbling, rollback coverage, and token-behavior tests directly support safe payments with non-standard ERC-20 tokens. The …
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: adding support for USDT and other non-standard ERC-20 tokens.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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_{A rabbit hops where token calls once failed
No-return coins now cross the trail
True and false are checked with care
Reverts return through open air
Batches roll back when paths derail
Chainvoice guards the payment trail}

_{Comment @coderabbitai help to get the list of available commands.}

[Anand-0037]

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[Anand-0037]

pr is ready for review, main design point is the custom handling of optional transferFrom return data in single and batch payments.