Implement runtime health filtering for vMCP backend requests

[yrobla]

Add two-layer health-based filtering to prevent tool calls to unhealthy backends. This protects users from timeouts and connection failures when backends become unhealthy during active sessions.

Large PR Justification

This is a complex feature that involves filtering unhealthy backends and remove them from capabilities. It also requires complex testing, so the PR can't be splitted.

[github-actions]

Large PR Detected

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## Large PR Justification

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- Generated code that cannot be split
- Large refactoring that must be atomic
- Multiple related changes that would break if separated
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[codecov]

Codecov Report

❌ Patch coverage is 53.44828% with 81 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.06%. Comparing base (24a6b2c) to head (598e21d).

Files with missing lines	Patch %	Lines
...perator/controllers/virtualmcpserver_controller.go	39.78%	54 Missing and 2 partials ⚠️
cmd/vmcp/app/commands.go	0.00%	8 Missing ⚠️
pkg/vmcp/health/monitor.go	0.00%	6 Missing ⚠️
pkg/vmcp/server/adapter/handler_factory.go	72.72%	3 Missing and 3 partials ⚠️
cmd/thv-operator/pkg/vmcpconfig/converter.go	0.00%	3 Missing ⚠️
pkg/vmcp/discovery/manager.go	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                             Coverage Diff                              @@
##           feat/issue-3036-healthcheck-circuitbreaker    #3144    +/-   ##
============================================================================
  Coverage                                       57.05%   57.06%            
============================================================================
  Files                                             342      343     +1     
  Lines                                           34332    34434   +102     
============================================================================
+ Hits                                            19589    19650    +61     
- Misses                                          13126    13167    +41     
  Partials                                         1617     1617            

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[Copilot]

Pull request overview

This PR implements two-layer health-based filtering to protect users from timeouts and connection failures when backends become unhealthy during active sessions. Layer 1 filters backends at capability discovery time (in the middleware), excluding unhealthy backends' tools/resources/prompts from being advertised to clients. Layer 2 performs runtime health checks before executing tool/resource/prompt requests, rejecting calls to backends that became unhealthy after session initialization.

Key changes:

• Added StatusProvider interface and IsBackendUsable helper function for health status queries
• Implemented backend health filtering in discovery middleware
• Added runtime health checks in handler factory before tool/resource/prompt execution

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/vmcp/health/monitor.go	Adds StatusProvider interface and IsBackendUsable helper for health status queries
pkg/vmcp/discovery/health_filter.go	Implements backend filtering logic to exclude unhealthy/unauthenticated backends from capabilities
pkg/vmcp/discovery/health_filter_test.go	Comprehensive unit tests for health filtering logic including edge cases
pkg/vmcp/discovery/middleware.go	Integrates health filtering into discovery middleware (Layer 1 filtering)
pkg/vmcp/discovery/middleware_test.go	Tests for middleware health filtering behavior
pkg/vmcp/server/adapter/handler_factory.go	Adds runtime health checks before tool/resource/prompt execution (Layer 2 filtering)
pkg/vmcp/server/adapter/handler_factory_test.go	Tests for runtime health checks in handler factory
pkg/vmcp/server/server.go	Updates health monitor initialization order and middleware setup
test/e2e/thv-operator/virtualmcp/virtualmcp_circuit_breaker_test.go	E2E tests verifying both filtering layers work correctly
examples/vmcp-config.yaml	Updates comments to document health monitoring and capability filtering behavior
examples/operator/virtual-mcps/vmcp_health_monitoring.yaml	Enhanced documentation explaining capability filtering when health monitoring is enabled

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[github-actions]

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

Large PR justification has been provided. Thank you!

[Copilot]

Pull request overview

Copilot reviewed 22 out of 22 changed files in this pull request and generated 1 comment.

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