[BUG] closeVault() fails with USDC balance - account merge requires zero non-native balances

[thisisouvik]

Description

The closeVault() function in backend/src/stellar/vault.ts calls mergeAccount() which merges all XLM back to the user's wallet but does NOT first remove the USDC trustline or transfer any USDC balance. The Stellar protocol requires all non-native asset balances to be zero before an account merge. If a vault holds any USDC, closeVault() will throw op_has_sub_entries and the vault cannot be closed.

Steps to Reproduce

1. Create a savings vault.
2. Send USDC to the vault.
3. Call the vault close endpoint.
4. Observe Stellar error: op_has_sub_entries.

Expected Behavior

Before merging: (1) Transfer all USDC back to user wallet, (2) Remove USDC trustline with changeTrust limit 0, (3) Then merge the account.

Impact

Medium - Users who receive USDC in vaults cannot close them, permanently locking their XLM reserve.

[nwabaj2017]

@nwabaj2017 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello maintainer, I'd be delighted to work on this. Please assign

ℹ️ Repo Maintainers: To accept this application, review their application or assign @nwabaj2017 to this issue.

[sourirashmi2004]

@sourirashmi2004 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

i would like to work in this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @sourirashmi2004 to this issue.

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This issue has been completed by @sourirashmi2004 as part of the Stellar Wave Program's 8th Wave 🥳

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