test: Add comprehensive unit tests for hardware manager lifecycle

[jra3]

Summary

The hardware manager (internal/hardware/manager.go) currently has 0% test coverage despite being a critical 297-line component responsible for hardware discovery lifecycle management.

Background

The hardware manager coordinates:

• Periodic hardware discovery scheduling
• Performance collector integration
• Graceful startup/shutdown lifecycle
• Error handling and recovery
• Resource cleanup

Missing Test Coverage

Critical Functions (0% coverage):

• NewManager - Constructor validation
• Start - Startup sequence and initial discovery
• Stop - Graceful shutdown coordination
• runPeriodicUpdates - Periodic scheduling logic
• updateHardwareGraph - Core update orchestration
• collectHardwareSnapshot - Performance collector integration

Test Implementation Plan

1. Lifecycle Tests

func TestManager_Lifecycle(t *testing.T) {
    // Test successful Start/Stop coordination
    // Test context cancellation propagation
    // Test WaitGroup synchronization
}

2. Error Handling Tests

func TestManager_StartupErrors(t *testing.T) {
    // Test initial discovery failures (non-fatal)
    // Test performance manager integration errors
    // Test resource store failures
}

3. Periodic Update Tests

func TestManager_PeriodicUpdates(t *testing.T) {
    // Test timer-based updates
    // Test update failure recovery
    // Test shutdown during update
}

4. Collector Integration Tests

func TestManager_CollectorIntegration(t *testing.T) {
    // Test partial collector failures
    // Test collector timeout handling
    // Test snapshot assembly
}

Success Criteria

• Achieve >80% test coverage for manager.go
• Test all public methods and critical private methods
• Cover error paths and edge cases
• Validate proper resource cleanup
• Test concurrent access patterns

Priority

HIGH - This component manages the entire hardware discovery subsystem and lacks any test coverage.

Related

Part of hardware discovery feature testing improvements following initial implementation.