feat: implement HalfOpen timeout and automatic breaker promotion logic

[Sendi0011]

Implement Half-Open Timeout Handling and Automatic Circuit Breaker Promotion

Overview

This PR implements the missing timeout logic for the circuit breaker in contracts/program-escrow/src/lib.rs as requested in Issue #1254. The circuit breaker now supports automatic transitions from Open to HalfOpen after a configurable recovery window, and from HalfOpen to Closed after successful probe operations.

Closes #1254

Changes Made

Core Implementation

1. Enhanced Circuit Breaker Configuration

• Added recovery_window parameter to CircuitBreakerConfig
• Updated configure_circuit_breaker API to accept recovery window (breaking change)
• Default recovery window: 300 seconds (5 minutes)

2. Automatic Timeout Transitions

• check_timeout_transitions(): New function that checks and applies automatic state transitions
• Open → HalfOpen: Automatically transitions after recovery_window seconds have elapsed since opened_at
• HalfOpen → Closed: Existing logic enhanced - transitions after success_threshold successful operations
• Failure handling: Failed operations in HalfOpen restart the Open timer with a new opened_at timestamp

3. Enhanced State Management

• Timestamp tracking: opened_at is stored when circuit transitions to Open
• Automatic checks: check_and_allow() now calls check_timeout_transitions() before state evaluation
• Event emission: New cb_timeout event emitted for automatic transitions

4. Updated Status Interface

• CircuitBreakerStatus now includes recovery_window field
• get_circuit_breaker_status() returns complete configuration including timeout settings

Security & Safety

Invariant Preservation

• All existing circuit breaker invariants are maintained
• opened_at timestamp is always set when transitioning to Open
• Timeout calculations use ledger timestamps for reliability
• Authorization checks remain unchanged

Event Auditing

• cb_timeout events for automatic transitions with reason codes
• Backward compatibility for all existing events
• Complete audit trail of all state changes

API Changes

Breaking Changes

// OLD API
configure_circuit_breaker(caller, failure_threshold, success_threshold, max_error_log)

// NEW API  
configure_circuit_breaker(caller, failure_threshold, success_threshold, max_error_log, recovery_window)

New Fields

pub struct CircuitBreakerStatus {
    // ... existing fields ...
    pub recovery_window: u64,  // NEW: timeout configuration
}

pub struct CircuitBreakerConfig {
    // ... existing fields ...
    pub recovery_window: u64,  // NEW: automatic recovery timeout
}

Files Modified

Core Implementation

• contracts/program-escrow/src/error_recovery.rs: Enhanced with timeout logic
• contracts/program-escrow/src/lib.rs: Updated API signature and module declarations

Test Updates

• contracts/program-escrow/src/test_circuit_breaker_enforcement.rs: Fixed corrupted test
• contracts/program-escrow/src/rbac_tests.rs: Updated API calls
• contracts/program-escrow/src/test_circuit_breaker_audit.rs: Updated API calls
• contracts/program-escrow/src/test_circuit_breaker_timeout.rs: New comprehensive timeout tests

Documentation

• docs/program-escrow/circuit-breaker.md: Complete documentation with examples, best practices, and troubleshooting

Behavior Examples

Automatic Recovery Scenario

1. Circuit opens due to failures at timestamp 1000
2. opened_at = 1000 is stored
3. recovery_window = 300 (5 minutes)
4. At timestamp 1350+ any operation triggers:
   - check_timeout_transitions() detects 1350 >= 1000 + 300
   - Circuit automatically transitions to HalfOpen
   - cb_timeout event emitted with reason "auto_half"
5. Next successful operation closes circuit

Configuration Example

// Configure 10-minute recovery window
client.configure_circuit_breaker(
    &admin,
    &3u32,    // failure_threshold  
    &1u32,    // success_threshold
    &10u32,   // max_error_log
    &600u64   // recovery_window (10 minutes)
);

Testing Strategy

Comprehensive Test Coverage

• Automatic timeout transitions with various recovery windows
• Edge cases: zero recovery window, very large windows
• Integration testing with existing circuit breaker logic
• Event emission verification for audit trails
• Security testing for unauthorized access prevention
• Multiple timeout cycles and configuration changes

Test Categories

1. Core timeout functionality: Open→HalfOpen→Closed flows
2. Configuration management: Recovery window updates
3. Edge cases: Zero/large timeouts, multiple cycles
4. Integration: Compatibility with manual resets
5. Security: Authorization and invariant preservation

Security Considerations

Timestamp Security

• Uses ledger timestamps for reliable, tamper-resistant timing
• opened_at is always set consistently when opening circuit
• Timeout calculations are deterministic and verifiable

Authorization Unchanged

• All existing admin controls preserved
• Manual reset functionality remains available
• Configuration changes still require admin authorization

Invariant Safety

• Circuit state transitions maintain all existing invariants
• verify_circuit_invariants() passes for all new states
• No funds can be stranded due to timeout logic

Backward Compatibility

Breaking Changes

• API signature change: configure_circuit_breaker now requires recovery_window parameter
• Existing deployments: Will need to update configuration calls

Preserved Functionality

• All existing events continue to be emitted
• Manual reset behavior unchanged
• Circuit state semantics preserved
• Error handling logic unchanged

Performance Impact

Minimal Overhead

• Timeout check is O(1) operation
• Only executes during operation attempts
• No background processes or timers
• Leverages existing ledger timestamp access

Storage Impact

• Single additional field in configuration
• No new storage keys required
• Existing persistent storage patterns maintained

Documentation

Complete Documentation Package

• API reference with all function signatures
• Configuration examples for different scenarios
• Best practices for recovery window tuning
• Troubleshooting guide for common issues
• Migration notes for upgrading existing deployments
• Event reference for monitoring systems

Future Enhancements

This implementation provides a solid foundation for future enhancements:

• Adaptive recovery windows based on failure patterns
• Circuit breaker metrics and health monitoring
• Integration with external monitoring systems
• Advanced failure classification and response strategies

Verification

Manual Testing Checklist

• Circuit opens after failure threshold
• Automatic transition to HalfOpen after recovery window
• Successful probe closes circuit
• Failed probe reopens circuit with new timer
• Configuration changes take effect immediately
• Events are emitted correctly
• Status endpoint reflects current state and config

Integration Testing

• Compatible with existing payout operations
• Works with batch and single payouts
• Integrates with manual admin resets
• Preserves all security invariants

Deployment Notes

Configuration Migration

Existing deployments will need to update their configuration calls:

// Update from:
configure_circuit_breaker(&admin, &3, &1, &10);

// To:
configure_circuit_breaker(&admin, &3, &1, &10, &300);

Recommended Settings

• Development: 60-300 seconds (1-5 minutes)
• Staging: 300-900 seconds (5-15 minutes)
• Production: 300-1800 seconds (5-30 minutes)

---

This implementation fully addresses Issue #1254 requirements:
✅ Store opened_at ledger timestamp when circuit transitions to Open
✅ After configurable recovery_window ledgers, allow one probe request (HalfOpen)
✅ On probe success transition to Closed; on failure restart Open timer
✅ Secure, tested, and documented implementation
✅ Efficient and easy to review code structure

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