[CT-13] Implement reputation score time-decay function

[mftee]

Problem

A carrier who performed excellently two years ago but has been inactive retains their peak score indefinitely. Old ratings are weighted equally with recent ones, meaning the score does not reflect a carrier's current reliability — a key piece of information for shippers choosing between carriers.

Proposed Solution

Implement a time-decay weighting algorithm in a new reputation contract inside contracts/package/reputation-decay/ that reduces the influence of older ratings on the composite score.

Note: All work must be done inside the contracts/package/ directory. Do not modify any existing contract files outside this folder.

Acceptance Criteria

• Ratings less than 365 days old contribute at 100% weight
• Ratings between 365-730 days old contribute at 70% weight
• Ratings older than 730 days contribute at 40% weight
• get_decayed_score(user_id, current_ledger_time) applies decay weights and returns the adjusted composite score (0-1000)
• Decay thresholds and weight factors are configurable at contract initialization (stored in persistent storage)
• Unit tests verify decay math for ratings at exactly 0 days, 366 days, and 731 days old using fixed input values and expected outputs

[limxiy]

@limxiy has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I’d like to work on this issue. I have experience implementing scoring and weighted-calculation logic in Soroban smart contracts, and I can build the reputation decay contract with configurable thresholds and deterministic decay calculations.

Planned implementation:

• Create the new reputation-decay contract inside contracts/package/

• Implement configurable decay thresholds and weight factors stored in persistent storage during initialization

• Add get_decayed_score(user_id, current_ledger_time) to calculate weighted composite reputation scores

• Apply decay rules:

  • <365 days → 100% weight
  • 365–730 days → 70% weight

  • 730 days → 40% weight

• Ensure scores are normalized within the 0–1000 range

• Add unit tests validating exact decay behavior at 0 days, 366 days, and 731 days using fixed expected outputs

All work will remain scoped to:

• contracts/package/reputation-decay/

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

[Menjay7]

@Menjay7 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi! I’m a full-stack developer with a strong blockchain background. I’d love to handle this issue and can deliver a clean, reliable solution. Kindly assign it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Menjay7 to this issue.

[Blckjiggy]

@Blckjiggy has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Can this be assigned to me? I'd like to work on this

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

[drips-wave]

Congratulations, @limxiy! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @limxiy: 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

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