Add deterministic contract event replay metadata

[grantfox-oss]

Impact: Contract events currently emit raw payloads without deterministic replay metadata, making it difficult for backend consumers and indexers to reconcile repeated or replayed event deliveries.

Affected areas: app/contract/contracts/Folder/src/events.rs, app/contract/contracts/Folder/src/metadata.rs, app/backend/src/ingestion/soroban-event.parser.ts, app/backend/src/ingestion/event.repository.ts, ingestion tests/docs.

Implementation scope:

• Add explicit replay metadata to emitted events, such as originating transaction hash, sequence number, and stable event version.
• Ensure event payloads include enough identity to safely deduplicate repeated deliveries.
• Update backend event parser to persist and validate replay metadata.
• Add tests for event replay, duplicate delivery, and out-of-order handling.

Acceptance criteria:

• Backend indexer can detect duplicate event deliveries using contract-provided metadata.
• Event replay metadata is included in all persisted contract events.
• Tests prove idempotent ingestion on repeated Horizon deliveries.

[Just-Bamford]

Hi maintainer, I'd like to work on this issue. My approach is to introduce a consistent replay metadata contract for all emitted events by including a stable event version and deterministic identity fields required for idempotent processing. I'll update the backend parser and persistence layer to validate and store this metadata, implement deduplication based on the replay identifiers, and add tests covering duplicate deliveries, replay scenarios, and out-of-order events to ensure reliable ingestion.

[feyishola]

Hi im Feyishola a software developer with over 4 years of experience. pls i would love to work on this

[grantfox-oss]

🦊 GrantFox — @feyishola 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 #52)
2. Your PR will be reviewed by the BlockDash-Studios maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@feyishola's PR #63 was approved and merged by @MaryammAli.

🏆 @feyishola: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (223 total points). Track your full progress on GrantFox.

👏 Great work, @feyishola! Keep contributing to BlockDash-Studios.