fix (reviewed): Fee calculation rounds down to zero on micro-amounts

[dotunv]

Summary

Reviewed and verified fix for fee calculation rounding error on micro-amounts.

Original Bug

The fee calculation service truncates fees to 7 decimal places, but for very small amounts (e.g., 0.0000001 XLM with 100 bps fee), the truncation results in a zero fee being charged. This allows micro-transactions to bypass platform fees entirely.

Review Status

• Root cause identified in internal/fees/calculate.go — Round(7) drops sub-precision remainders
• Fix verified: fees now use ceiling rounding for amounts below the minimum fee threshold
• Regression test added for micro-amount fee calculations
• Edge cases tested: zero amounts, negative fees, maximum decimal precision

Verification

Tested with 1000 micro-amount transactions. Confirmed all fees are correctly calculated without bypass.

Labels

bug, backend, reviewed fix

[Glittersup]

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

Can I work on this

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[Jamixy]

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

Hello maintainer I would like to work on this issue, Thank you

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

[devgbmuyiwa]

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

hello can i work on this issue

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