Add regression test for GetMerchantContracts exception path #1868

Problem

The GetMerchantContracts read path currently has success and empty-list coverage, but not an explicit exception-path test.

Related investigation: TransactionProcessor#1836

Requested change

Add a test that forces an exception from the merchant contracts read path and verifies the failure is surfaced and logged clearly.

Suggested coverage

• TransactionProcessorManager.GetMerchantContracts(...) when the repository throws
• confirm the failure result is returned
• confirm the exception path is not silently converted into an ambiguous success or empty result

Notes

• Keep the test targeted to the explicit exception case.
• Prefer a minimal repro over broad integration coverage unless the issue requires a full database setup.

Acceptance criteria

• Exception-path test exists for merchant contracts retrieval
• The failure behavior is asserted clearly
• The test protects the regression seen in Sentry