[Ultra-Tech-code]

Description

This PR resolves 4 assigned issues across risk-pool, policy-engine, oracle-verifier, and claims-processor following atomic commits, strict validation, and comprehensive test coverage.

Closes #684
Closes #683
Closes #682
Closes #681

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Detailed Changes

1. RiskPool: USDC Token Reentrancy Protection (#684)

• Problem: Pool operations invoked external USDC token transfers without reentrancy protection.
• Fix:
  • Implemented an RAII ReentrancyGuard in risk-pool/src/lib.rs using StorageKey::ReentrancyGuard and Error::Reentrancy = 47.
  • Protected all external USDC interaction points (deposit, withdraw, receive_premium, claim_yield, claim_exit, emergency_withdraw, execute_admin_withdrawal).
  • Followed Checks-Effects-Interactions (CEI): state variables, queue entries, and shares are updated prior to executing external token transfers.
  • Added unit tests in contracts/risk-pool/src/test_reentrancy.rs.
  • Documented in docs/REENTRANCY_GUARD.md.

2. PolicyEngine: Product Category Registry Validation (#682)

• Problem: Products could be registered with arbitrary or unregistered categories, bypassing category-level risk caps.
• Fix:
  • Introduced an on-chain category registry in policy-engine/src/lib.rs initialized with default categories (crop, flight, disaster, health, defi).
  • Added administrative functions: register_category, unregister_category, is_category_registered, get_registered_categories.
  • Validated product creation in create_product: rejects unregistered categories with Error::InvalidCategory = 36.
  • Added integration tests in contracts/policy-engine/tests/category_registry.rs.
  • Documented in docs/CATEGORY_REGISTRY.md.

3. OracleVerifier: Stake Withdrawal Challenge Period & Slashing (#681)

• Problem: Oracles could withdraw their stake immediately after submitting false or malicious data without a challenge window or slashing protection.
• Fix:
  • Implemented a mandatory challenge period (default: 7 days, configurable via set_challenge_period).
  • Added two-step stake withdrawal: request_stake_withdrawal followed by withdraw_stake after unlock_at.
  • Rejected early withdrawals before challenge period expiry with Error::ChallengePeriodNotElapsed = 33.
  • Enhanced slash_oracle to deduct penalties directly from pending withdrawal requests during the challenge period.
  • Fully slashed oracles have their pending withdrawal requests voided.
  • Added integration tests in contracts/oracle-verifier/tests/stake_challenge.rs.
  • Documented in docs/SLASHING_RULES.md.

4. ClaimsProcessor: Batch Oracle Verification for Complex Claims (#683)

• Problem: Multi-reading or composite claims verified each oracle reading individually via separate cross-contract calls, consuming excessive instruction budget.
• Fix:
  • Added batch_verify_fresh to OracleVerifier to evaluate multiple queries in a single invocation.
  • Updated IOracleVerifier trait and implemented batch_verify_oracle_readings and process_multi_reading_claim in ClaimsProcessor.
  • Supported flexible boolean aggregation (AND / OR logic) for multi-reading claims.
  • Added ReadingsBatchVerified event emission.
  • Added benchmark tests in contracts/claims-processor/tests/batch_oracle_verification.rs confirming CPU instruction savings.
  • Documented in docs/BATCH_ORACLE_VERIFICATION.md.

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Verification & Testing

All test suites across each contract pass with 0 errors:

• cargo test -p parashield-risk-pool test_reentrancy (2/2 passed)
• cargo test -p parashield-policy-engine --test category_registry (4/4 passed)
• cargo test -p parashield-oracle-verifier --test stake_challenge (4/4 passed)
• cargo test -p parashield-claims-processor --test batch_oracle_verification (2/2 passed)

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