test: Add confidential mpt bulletproof tests

[oleks-rip]

High Level Overview of Change

Add ConfidentialMPTTransfer and ConfidentialMPTConvertBack bulletproof tests that trying spend / convert more than user have on their balance / convert to MPT.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[oleks-rip]

2026-07-22T19:08:34.7946773Z /__w/rippled/rippled/src/test/app/ConfidentialTransfer_test.cpp:5498:54: runtime error: unsigned integer overflow: 100 - 101 cannot be represented in type 'uint64_t' (aka 'unsigned long')
2026-07-22T19:08:34.7947982Z SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /__w/rippled/rippled/src/test/app/ConfidentialTransfer_test.cpp:5498:54 

This ubsan report about UB(and 2 failing tests) is incorrect

[Copilot]

Pull request overview

Adds a new regression test in the confidential MPT transfer suite to validate that an attempted “overdraft” (sending more than the sender’s confidential balance) is rejected by range-proof verification, and updates UBSan suppressions accordingly.

Changes:

• Add testSendOverdraftBulletproof that constructs a proof manually to bypass client-side checks and verifies ledger-side rejection for overdraft amounts.
• Wire the new test into the existing confidential send negative-test sequence.
• Add an UBSan suppression entry for unsigned overflow in the test file.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/test/app/ConfidentialTransfer_test.cpp	Adds a new overdraft-focused bulletproof/range-proof negative test and hooks it into the test run.
sanitizers/suppressions/ubsan.supp	Adds a UBSan suppression for unsigned wraparound triggered by the new test logic.

Comments suppressed due to low confidence (1)

src/test/app/ConfidentialTransfer_test.cpp:5558

• recipients is constructed but never used. With -Wall (and builds enabling -Werror), this triggers an unused-variable warning/error and will break the build. Since the proof is built directly from c2Vec/pkVec below, this block can be removed.

        // Build recipients for sigma proof
        std::vector<ConfidentialRecipient> recipients;
        recipients.push_back({
            .publicKey = Slice(requireOptional(mptIssuer.getPubKey(alice), "Missing alice pubkey")),
            .encryptedAmount = aliceEncAmt,

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.