Contract upgrade and versioning

[codebestia]

Write contracts/docs/concepts-upgrades.md centred on token_transfer's upgrade(env, new_wasm_hash): who may call it, how a new WASM hash is produced and verified, and the storage-compatibility rules that make an upgrade safe.

Acceptance criteria:

• Documents the authorization required to upgrade and the consequence of that key being compromised
• Gives the end-to-end procedure: build, hash, verify, invoke, confirm
• Documents storage-layout compatibility rules — which changes are safe across an upgrade and which corrupt existing state
• States which contracts are upgradeable and which are not

[official-rex]

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

I’d like to work on this issue. I can document the upgrade authorization, WASM hash verification, storage compatibility rules, and upgradeable contracts clearly.

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

[Depo-dev]

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

Hello team.

I’m Depodev, a software engineer with a strong background in building scalable systems and contributing to open-source projects. I’ve taken some time to go through the repository and understand the current implementation, and I’m clear on the issue, its context, and the expected outcome.

I’d love to work on this and take ownership of the fix. I’m confident I can cleanly resolve it while keeping everything aligned with the existing codebase and ensuring all criteria are met. Would appreciate being assigned to this issue.

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

[drips-wave]

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

🧑‍💻 @Depo-dev: 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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[github-actions]

Closed by #592, merged into dev.

[drips-wave]

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

😎 @Depo-dev: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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