Group file sharing over MLS

[codebestia]

Encrypt the file once; distribute the file key inside the MLS-encrypted group message. All members derive the same key from group state. Reuses the file subsystem with single-ciphertext group delivery.

Acceptance criteria:

• One file key shared via MLS to the whole group
• Members decrypt with the shared key
• Removed members lose access going forward (post-rekey)

[GdAyo19]

@GdAyo19 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I would love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @GdAyo19 to this issue.

[Olorunfemi20]

@Olorunfemi20 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello! I'm interested in tackling this issue. I've reviewed the task and I'm confident in my ability to deliver a reliable implementation. I'll keep the changes focused, communicate any important findings during development, and submit a well-tested pull request.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Olorunfemi20 to this issue.

[ndyugwu]

@ndyugwu has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

i would like to work on this issue kindly assign me

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

[drips-wave]

Congratulations, @Olorunfemi20! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @Olorunfemi20: 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.

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