Implement circuit breaker for vMCP backend health monitoring

[yrobla]

Add circuit breaker pattern to the vMCP health monitoring system to prevent cascading failures and enable graceful degradation when backends become unhealthy. The circuit breaker fast-fails health checks when backends are down, reducing unnecessary network calls and allowing faster recovery.

Implementation:

• Add circuit breaker to health monitoring system (pkg/vmcp/health/)
• Circuit states map to health states (Closed→Healthy, Open→Unhealthy, HalfOpen→Degraded)
• Per-backend circuit isolation - each backend has independent circuit state
• Configurable failure threshold and timeout for circuit transitions
• Fast-fail behavior skips health checks when circuit is open

Configuration:

• Disabled by default for backward compatibility
• Optional circuit_breaker config in VirtualMCPServer operational settings
• Configurable failure_threshold and timeout parameters

Testing:

• Unit tests for circuit state machine logic (circuit_breaker_test.go)
• Integration tests with health monitor (monitor_test.go)
• End-to-end tests in Kubernetes environment (virtualmcp_circuit_breaker_test.go)
• All tests run in parallel for faster execution

The circuit breaker opens after consecutive failures, transitions to half-open after timeout, and closes on successful recovery. This prevents overwhelming failing backends while maintaining healthy backend availability.

🤖 Generated with Claude Code

Large PR Justification

This PR implements the circuit breaker pattern for vMCP backend health monitoring as a single atomic feature. The circuit breaker logic is tightly coupled across multiple health system components (status tracker, monitor, config) that must work together - splitting would create intermediate states where the feature is incomplete or broken. The configuration flows through multiple layers (YAML → commands → server → monitor → status), and separating config from implementation would leave the system non-functional. Additionally, the circuit states (Closed/Open/HalfOpen) map directly to health states (Healthy/Unhealthy/Degraded), a contract that must be established atomically.

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 88.80597% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.05%. Comparing base (5d3dc03) to head (24a6b2c).

Files with missing lines	Patch %	Lines
cmd/vmcp/app/commands.go	0.00%	8 Missing ⚠️
pkg/vmcp/health/status.go	93.00%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@                        Coverage Diff                        @@
##           feat/issue-3036-healthcheck-3    #3136      +/-   ##
=================================================================
+ Coverage                          56.93%   57.05%   +0.12%     
=================================================================
  Files                                341      342       +1     
  Lines                              34201    34332     +131     
=================================================================
+ Hits                               19471    19589     +118     
- Misses                             13114    13126      +12     
- Partials                            1616     1617       +1     

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Large PR justification has been provided. Thank you!

[github-actions]

✅ Large PR justification has been provided. The size review has been dismissed and this PR can now proceed with normal review.

[Copilot]

Pull request overview

This PR implements a circuit breaker pattern for vMCP backend health monitoring to prevent cascading failures and enable graceful degradation. The circuit breaker fast-fails health checks when backends are down, reducing unnecessary network calls and allowing faster recovery.

Key changes:

• New circuit breaker state machine with three states (Closed, Open, HalfOpen) that map to health states (Healthy, Unhealthy, Degraded)
• Per-backend circuit isolation with independent state tracking for each backend
• Disabled by default for backward compatibility with configurable threshold and timeout parameters

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/vmcp/health/config.go	Defines circuit breaker configuration, validation logic, and state constants
pkg/vmcp/health/config_test.go	Unit tests for circuit breaker configuration validation and state string conversion
pkg/vmcp/health/circuit_breaker_test.go	Comprehensive unit tests for circuit breaker state machine logic and transitions
pkg/vmcp/health/status.go	Integrates circuit breaker into status tracker with state management methods
pkg/vmcp/health/status_test.go	Updates status tracker tests to pass circuit breaker config parameter
pkg/vmcp/health/monitor.go	Implements fast-fail logic by checking circuit state before health checks
pkg/vmcp/health/monitor_test.go	Integration tests for circuit breaker with health monitor including full cycle and backward compatibility tests
cmd/vmcp/app/commands.go	Maps circuit breaker configuration from YAML to health monitor config
cmd/vmcp/README.md	Comprehensive documentation of health monitoring and circuit breaker features
examples/operator/virtual-mcps/vmcp_health_monitoring.yaml	Example configuration demonstrating circuit breaker settings
test/e2e/thv-operator/virtualmcp/virtualmcp_circuit_breaker_test.go	End-to-end Kubernetes tests verifying circuit breaker behavior in production-like environment

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[yrobla]

pending on changes for status reporter abstraction