fix(operator): apply deprecated VirtualMCPServer inline telemetry

[RaviTharuma]

Summary

Fixes #6276: operator-managed VirtualMCPServer silently ignored
spec.config.telemetry after #4819, so
enablePrometheusMetricsPath: true never registered /metrics. Prometheus
scrapes then hit the MCP streamable-HTTP handler and got HTTP 406 JSON-RPC
(Client must accept text/event-stream) instead of Prometheus text.

This also unblocked collecting Go runtime series for #5860.

Changes

• Restore deprecated inline config.telemetry fallback when
  telemetryConfigRef is unset (TelemetryConfigRef still wins when both set)
• Log a migration warning pointing operators at MCPTelemetryConfig
• Unit tests for inline apply + ref precedence
• Docs: remove false “CEL mutual exclusion” claim; document 406 failure mode
  when telemetry is not configured

Preferred long-term path (unchanged)

apiVersion: toolhive.stacklok.dev/v1beta1
kind: MCPTelemetryConfig
metadata:
  name: vmcp-prometheus
spec:
  prometheus:
    enabled: true

with spec.telemetryConfigRef on VirtualMCPServer.

Test plan

• go test ./cmd/thv-operator/pkg/vmcpconfig/ -run 'TestConverter_InlineTelemetry|TestConverter_TelemetryConfigRefWins|TestConverter_TelemetryNil'
• CI unit / operator tests
• After merge: operator with only inline enablePrometheusMetricsPath: true
  should render telemetry into the vmcp ConfigMap and serve HTTP 200 on
  GET /metrics with Accept: text/plain

Security

No secrets, private hostnames, or customer data in this PR or linked issues.

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[ChrisJBurns]

Awaiting reply to #6276 (comment)

[Copilot]

Pull request overview

Restores operator support for the deprecated VirtualMCPServer.spec.config.telemetry by applying it as a fallback when spec.telemetryConfigRef is unset, so /metrics can be registered again for Prometheus scrapes while still preferring the shared MCPTelemetryConfig path.

Changes:

• Reintroduce inline telemetry normalization fallback (with a migration log message) when telemetryConfigRef is absent.
• Add/adjust unit tests to cover inline-telemetry application and ref-precedence behavior.
• Update observability docs to remove the incorrect “CEL mutual exclusion” claim and document the /metrics → MCP 406 failure mode when telemetry is not configured.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
docs/operator/virtualmcpserver-observability.md	Updates vMCP telemetry docs to describe inline fallback + 406 scrape symptom when telemetry is unset.
docs/observability.md	Aligns general observability docs with vMCP telemetry fallback behavior and failure mode.
cmd/thv-operator/pkg/vmcpconfig/converter.go	Restores deprecated inline telemetry fallback and emits a migration log message.
cmd/thv-operator/pkg/vmcpconfig/converter_test.go	Updates/adds tests for inline telemetry application and TelemetryConfigRef precedence.
cmd/thv-operator/pkg/spectoconfig/telemetry.go	Clarifies function usage in comments now that inline fallback is restored.

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[RaviTharuma]

Closing this in favor of the maintainer direction on #6276.

Restoring deprecated spec.config.telemetry is not what we want. Follow-up will keep inline as a no-op for the operator, emit a Warning so /metrics 406 is not silent, and align the docs with spec.telemetryConfigRef.

[RaviTharuma]

Closing per #6276: do not restore deprecated inline telemetry. Follow-up will add a Warning/validation + docs for the silent no-op.