Map mcp-go sentinel errors and poll registry version for timely status reports

[yrobla]

Summary

• Map transport.ErrUnauthorized to ErrAuthenticationFailed and transport.ErrLegacySSEServer to ErrBackendUnavailable in wrapBackendError, before the string-based fallback. This ensures 401 responses from mcp-go reach health monitoring as BackendUnauthenticated rather than BackendUnhealthy.
• Add "unauthorized (401)" pattern to IsAuthenticationError to match mcp-go's ErrUnauthorized string format (reversed order vs "401 unauthorized").
• Poll DynamicRegistry.Version() every 2s in periodicStatusReporting and trigger an immediate status report when the version changes, so backend additions/removals are reflected without waiting for the full 30s interval.

Fixes #4278

Type of change

• Bug fix
• New feature
• Refactoring (no behavior change)
• Dependency update
• Documentation
• Other (describe):

Test plan

• Unit tests (task test)
• E2E tests (task test-e2e)
• Linting (task lint-fix)
• Manual testing (describe below)

Changes

File	Change

Does this introduce a user-facing change?

Special notes for reviewers

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.12%. Comparing base (d96dbac) to head (d32dacb).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/vmcp/server/status_reporting.go	88.23%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4317      +/-   ##
==========================================
+ Coverage   69.09%   69.12%   +0.02%     
==========================================
  Files         477      477              
  Lines       48074    48099      +25     
==========================================
+ Hits        33216    33247      +31     
+ Misses      12276    12268       -8     
- Partials     2582     2584       +2     

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[Copilot]

Pull request overview

This PR improves vMCP health/status accuracy when using mcp-go by mapping specific transport-layer sentinel errors to vmcp sentinel errors and by making status reporting react quickly to dynamic backend registry changes (fixing cases where backends could remain “unhealthy” after startup races or registry removals).

Changes:

• Map mcp-go transport sentinel errors (ErrUnauthorized, ErrLegacySSEServer) to vmcp sentinel errors in wrapBackendError prior to string-based fallbacks.
• Expand IsAuthenticationError matching to include mcp-go’s "unauthorized (401)" string format.
• Add registry-version polling (every 2s) to trigger immediate status reports when dynamic backend registries change, plus new unit tests for the behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/vmcp/client/client.go	Maps mcp-go transport sentinel errors to vmcp sentinel errors before string fallbacks.
pkg/vmcp/client/client_test.go	Adds unit tests validating the new wrapBackendError sentinel mappings.
pkg/vmcp/errors.go	Extends auth error string detection to match "unauthorized (401)".
pkg/vmcp/health/checker_test.go	Adds test coverage for the new auth error string format and health categorization expectations.
pkg/vmcp/server/status_reporting.go	Polls dynamic registry version to trigger immediate status reports on backend add/remove changes.
pkg/vmcp/server/status_reporting_test.go	Adds unit test to ensure version changes trigger a status report without waiting for the full interval.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

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[jhrozek]

Code review comment on version-polling interval configuration.

[jhrozek]

that was really just a nit