[Feature]: Partial Milestone Payment Release

[SudiptaPaul-31]

🔍 Problem Statement

Description

Implement secure partial payment releases for milestone-based contracts. This allows clients to approve and release funds for individual milestones while ensuring escrow balance integrity and preventing double spending.

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Requirements

• Each milestone has an allocated amount — defined at contract creation.
• Client approves individual milestones — approval triggers release of that milestone’s funds.
• Contract releases only that milestone's funds — no excess withdrawal allowed.
• Prevent double spending/double release — enforce idempotency checks.
• Track remaining escrow balance — update after each release.
• Emit contract events — log approvals, releases, and balance updates.

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Acceptance Criteria

• ✅ Remaining escrow balance is tracked — contract state reflects updated balance after each release.
• ✅ Released amount cannot exceed milestone allocation — strict enforcement of limits.
• ✅ All important actions emit contract events — visible in transaction logs for transparency.
• ✅ Double release attempts are rejected — contract prevents duplicate payouts.
• ✅ Client-only authorization — only the client can approve and trigger milestone releases.
• ✅ Comprehensive contract tests — cover valid releases, invalid attempts, and edge cases.

📈 Expected Impact

High — Would significantly improve user experience

[israeloluwasegun293-stars]

@israeloluwasegun293-stars has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello, maintainer...
Please, kindly assign me this, i can handle it perfectly. Thanks!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @israeloluwasegun293-stars to this issue.