Add schema-version negotiation for the encrypted payload prefix (enc:v1 → enc:v2) in data_migration

[Baskarayelu]

📋 Description

The encrypted-payload helpers in data_migration/src/lib.rs use a hardcoded ENCRYPTED_PAYLOAD_PREFIX_V1 ("enc:v1:") for export_to_encrypted_payload / import_from_encrypted_payload. There is no version negotiation: a future enc:v2 payload would fail to parse with no clear path to coexist with enc:v1.

This issue adds prefix-based schema-version negotiation so importers can accept multiple encoded-payload versions and reject unknown ones cleanly.

Why this matters: encoding formats evolve. Hardcoding a single prefix forces a flag-day migration; versioned prefixes let enc:v1 and enc:v2 coexist during rollout and fail closed on unknown versions instead of silently misparsing.

🎯 Requirements & Context

Functional requirements

• Introduce a versioned prefix scheme (enc:v1:, enc:v2:) with an enum mapping prefix → version.
• import_from_encrypted_payload must dispatch on the prefix and reject unknown prefixes with MigrationError::IncompatibleVersion (fail closed).
• Preserve enc:v1 behavior exactly for backward compatibility.
• Keep the existing MAX_ENCRYPTED_PAYLOAD_BYTES size guard, recomputed per version.
• Keep the documented caveat that the prefix is encoding-only and provides no on-chain confidentiality.

Context & constraints

• Soroban SDK 21.7.7; additive — do not break existing enc:v1 round-trips.
• Tests run with cargo test -p data_migration.

🛠️ Suggested Execution

1. Fork & branch

git checkout -b feature/migration-enc-version-negotiation

2. Implement changes

• Add the versioned prefix dispatch in data_migration/src/lib.rs.
• Add /// doc comments on the version negotiation and the no-confidentiality caveat.

3. Test & commit

cargo test -p data_migration

• Cover edge cases: enc:v1 round-trip unchanged, unknown prefix rejected, truncated prefix, and oversize payload per version.

Example commit message

feat(data-migration): add enc:v1→enc:v2 prefix version negotiation, fail closed on unknown

✅ Acceptance Criteria & Guidelines

Requirement	Target
Versioned prefix dispatch, fail-closed on unknown	Required
enc:v1 backward compatibility preserved	Required
Coverage of negotiation paths	≥ 95%, all branches
Doc comments + no-confidentiality caveat	Required
cargo test -p data_migration + cargo clippy clean	Required
Timeframe	96 hours from assignment

💬 Community & Support

Join the Remitwise contributor community on Discord: https://discord.gg/CtQuPZFMA — comment when you pick this up. 🚀

[Dreamstore2046]

Opened PR #1044 for this: https://github.com/Remitwise-Org/Remitwise-Contracts/pull/1044\n\nScope: versioned �nc:v1/�nc:v2 prefix dispatch, v1 export compatibility preserved, unknown versions fail closed with MigrationError::IncompatibleVersion, plus focused negotiation tests and README updates.

[arisu6804]

Please consider assigning this issue to me, as I’m prepared to contribute wherever it’s needed, whether that involves protocol logic, interface creation, service-layer development, visual implementation, or cross-component coordination.

[grantfox-oss]

🦊 GrantFox — @arisu6804 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #1032)
2. Your PR will be reviewed by the Remitwise-Org maintainers

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