Add Muxed Account (M...) Address Support to Beneficiary Validation

[maugauwi-hash]

Area: Stellar Address Validation
Priority: Medium
Estimated Time: 2.5 hours

Description:
shared/stellar-validation-spec.md scopes validation to G... ed25519 public keys only. Stellar
also supports muxed accounts (M..., SEP-0023), which some wallets use for sub-account routing. If
a user pastes a muxed address as a beneficiary, both StellarAddress.swift and its Android
counterpart will currently reject it as invalid, even though it may be a legitimate destination.

Tasks:

• Decide whether muxed accounts should be accepted as beneficiary addresses (product decision)
• If yes, update shared/stellar-validation-spec.md with the M-address format and update both validators
• If no, add explicit, distinguishing error copy ("muxed accounts aren't supported yet") rather than
  a generic invalid-address message
• Add shared test fixtures for muxed addresses either way

[Venrable18]

@Venrable18 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Good day maintainer..

I’m a full-stack and test integration developer…. 

Please assign this task to me…



ℹ️ Repo Maintainers: To accept this application, review their application or assign @Venrable18 to this issue.

[Abdulrasaq1515]

@Abdulrasaq1515 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Please assign me, I would do a good job fixing it

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Abdulrasaq1515 to this issue.

[SupremeCarMart100]

@SupremeCarMart100 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer,
I’d really appreciate the opportunity to work on this issue. Having reviewed the acceptance criteria, I’m confident that I can submit a PR after being assigned.
Please kindly assign this issue to me.
Thank you!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @SupremeCarMart100 to this issue.

[longyi2]

@longyi2 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @longyi2 to this issue.

[johnsaviour56-ship-it]

@johnsaviour56-ship-it has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I woulld love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @johnsaviour56-ship-it to this issue.

[drips-wave]

Congratulations, @johnsaviour56-ship-it! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @johnsaviour56-ship-it: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@johnsaviour56-ship-it's PR #345 was approved and merged by @maugauwi-hash.

🏆 @johnsaviour56-ship-it: You earned 40 FoxPoints for this contribution! Your current tier: Builder (1,265 total points). Track your full progress on GrantFox.

👏 Great work, @johnsaviour56-ship-it! Keep contributing to ethos-protocol.