feat(runtime): implement migration failure recovery — Task 14

[simonovic86]

Summary

Implements robust agent migration with retry, fallback, and lease-aware recovery to handle failures gracefully while preserving the single-instance invariant (EI-1).

Key Components

Migration Retry & Fallback

• internal/migration/retry.go: Error classification (retriable, fatal, ambiguous) and exponential backoff calculation
• MigrateAgentWithRetry: Orchestrates retry loop across multiple candidate peers with fallback
• FS-2 safety: Ambiguous transfers (sent but no confirmation) trigger RECOVERY_REQUIRED rather than retrying to different targets

Peer Registry

• internal/registry/registry.go: Peer discovery with health tracking, caching prices/capabilities, and candidate filtering by price/capability/health
• SelectCandidates: Ordered peer selection for migration fallback

Lease State Transitions

• RevertHandoff(): HANDOFF_INITIATED → ACTIVE_OWNER when migration fails before transfer
• Recover(): RECOVERY_REQUIRED → ACTIVE_OWNER with fresh epoch (major+1) after detecting unresponsive owner
• Lease recovery in tick loop: Auto-recovers from RECOVERY_REQUIRED during periodic ticks

Configuration & CLI

• --migration-retries: Max retry attempts per target (default: 3)
• --migration-retry-delay: Initial backoff delay (default: 1s)
• internal/config/config.go: MigrationMaxRetries, MigrationRetryDelay fields with validation

Main Loop Refactoring

• handleTick(): Encapsulates lease check, agent tick, and divergence verification
• applyCLIOverrides(): Consolidated CLI flag handling
• Tick result enum: Distinguishes normal/fast-path/recovery/stopped outcomes

Supporting Changes

• internal/pricing/service.go: ScanPeerPrices() for bulk peer price queries during migration decisions
• internal/p2p/node.go: ConnectedPeers() for discovering migration candidates
• ROADMAP.md: Updated to Phase 5 (Hardening); Tasks 12–14 marked complete

Safety Properties

• FS-1 (Migration Continuity): Source retains authority until target confirms
• FS-2 (Migration Continuity): Ambiguous transfers do not retry to different targets
• EI-1 (Single Active Instance): Enforced via lease state transitions and registry tracking
• Epoch versioning: Major version increment on recovery prevents stale lease conflicts

Testing

• Comprehensive unit tests for retry classification, backoff, registry filtering, and lease state transitions
• Error path coverage: timeouts, connection failures, rejections, ambiguous cases

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