Oracle Failure & Manipulation Testing

[UlyanaAndrukhiv]

Closes: #149

Note: this PR should be merged after

• Multiple Collateral Types & Cross-Asset Operations Testing #165

Description

Adds comprehensive test coverage for oracle failure modes, extreme price scenarios, and DEX/oracle price deviation circuit breaker to ensure the protocol maintains security when price data is compromised, unavailable, or manipulated.

Tests added (fork_oracle_edge_cases_test.cdc)

Price Feed Failures

• test_oracle_nil_price — oracle returns nil for FLOW; any operation requiring pricing (health check) must revert due to force-unwrap panic

Invalid Price Data

• test_oracle_zero_price — oracle price set to 0.0; position creation fails with PriceOracle must return a price greater than 0.0 if available postcondition
• test_oracle_near_zero_price_extreme_health — FLOW price set to $0.00000001; health drops to near-zero (0.000000016), position becomes liquidatable
• test_oracle_very_large_price_no_overflow — WETH price set to UFix64.max; verifies no overflow in UFix128 math, health returns CEILING_HEALTH, available balance unchanged

DEX/Oracle Price Deviation & Circuit Breaker

• test_dex_oracle_deviation_boundary_exact_threshold — boundary tests for dexOraclePriceDeviationInRange helper at exactly 300 bps, 301 bps, both directions, and equal prices
• test_dex_oracle_deviation_blocks_liquidation — DEX price deviates 16.7% from oracle; liquidation blocked with DEX/oracle price deviation too large
• test_dex_oracle_within_threshold_liquidation_succeeds — DEX price within 3% of oracle; liquidation proceeds normally
• test_governance_tightens_dex_deviation_threshold — governance tightens threshold from 300 bps to 100 bps; previously allowed 2.19% deviation now blocked

Extreme Price Scenarios

• test_flash_crash_triggers_liquidation — FLOW drops 50% ($1.00 → $0.50) in single block; health drops from 1.33 to 0.67, position becomes liquidatable, full liquidation flow executed and verified
• test_flash_pump_increase_doubles_health — FLOW doubles ($1.00 → $2.00); health jumps from 1.6 to 3.2, user borrows at inflated price, price corrects back demonstrating pump-and-dump risk