Fix resolver role rotation in settlement contract

[dDevAhmed]

📚 Overview

Old settlement contracts retain privileges after upgrade.

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🌊 Drips Context

This is a security risk affecting protocol governance.

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❗ Problem

• New role granted
• Old role NOT revoked

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✅ Expected Behavior

• Only current settlement contract has resolver role

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🧠 Implementation Guidelines

• Track previous contract
• Revoke role on update
• Emit rotation event

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✅ Acceptance Criteria

• Old contract loses role
• Tests confirm role rotation

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⏳ Complexity

Medium

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🏷 Labels

audit, security, drips-wave