feature/storage-ttl-v2-and-safe-pause-guards

[preciousadeyemi78]

Feat: Storage TTL v2 & Safe Pause Guards

Overview

This PR delivers two critical operational and security enhancements:

• Storage TTL v2 – Per-record expiration with auto-extend on activity
• Safe Pause Guards – Granular pausing with immutable emergency mode

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Issue 1: Storage TTL Strategy v2 (#307)

Changes

• Implemented per-record TTL helpers that set/extend expiration based on activity
• Defined TTL policies per record type (escrow, dispute, nonce, fee config)
• Added automatic TTL extension on read/write operations for active records
• Added tests simulating aging ledgers to verify retention behavior
• Ensured cleanup pathways do not break active escrows

Acceptance Criteria Met

• ✅ Active records stay alive without manual extension
• ✅ Inactive records expire according to policy
• ✅ Tests validate TTL behavior for multiple record types

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Issue 2: Safe Pause Guards (#306)

Changes

• Implemented emergency mode flag that cannot be reverted (immutable)
• Added granular feature-level pause flags (permission-specific, not global)
• Created minimal "safe-only" allowed entry point list (refunds/withdrawals remain available)
• Added comprehensive tests for every paused/allowed call under each mode
• All state transitions emit auditable events

Acceptance Criteria Met

• ✅ Emergency mode reliably blocks risky entry points
• ✅ Refund/withdrawal safety paths remain available
• ✅ State transitions are auditable via events

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Files Modified

contracts/
├── storage/
│ ├── ttl_[helpers.rs](https://helpers.rs/) # Per-record TTL logic
│ └── ttl_[policy.rs](https://policy.rs/) # Policy definitions per record type
├── security/
│ ├── pause_[guards.rs](https://guards.rs/) # Granular + emergency pause
│ └── safe_[mode.rs](https://mode.rs/) # Safe-only entry point list
└── tests/
├── ttl_[tests.rs](https://tests.rs/) # Aging ledger simulations
└── pause_[tests.rs](https://tests.rs/) # Pause mode coverage

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Evidence

• TTL auto-extend verified on read/write activity
• Inactive records expire correctly per policy
• Emergency mode permanently blocks risky entry points
• Refund/withdraw paths remain functional in emergency mode
• All tests pass with simulated ledger aging
• Events emitted for all pause state transitions

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Closes #307
Closes #306

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[preciousadeyemi78]

@Cedarich please, approve workflow to run.