Add tests for horizontal scaling operator behaviors

[yrobla]

Summary

Adds test coverage for the horizontal scaling operator behaviors introduced in
the companion PRs (THV-0047). The existing unit tests were added incrementally
with each implementation task; this PR closes gaps at three levels:

Unit tests (cmd/thv-operator/controllers/):

• TestConfigMapContent_SessionStorage: verifies ensureVmcpConfigConfigMap
  produces a ConfigMap YAML with sessionStorage populated when
  provider=redis, and absent when nil or memory.
• TestDeploymentForVirtualMCPServer_WithRedisPassword: verifies
  deploymentForVirtualMCPServer injects THV_SESSION_REDIS_PASSWORD as a
  SecretKeyRef env var and never as a plaintext value.

Integration tests (envtest — cmd/thv-operator/test-integration/):

• MCPServer: ScalingConfig (backend_replicas + session_redis) is written
  to the RunConfig ConfigMap when backendReplicas and Redis sessionStorage
  are set; omitted when absent.
• VirtualMCPServer: spec.replicas=3 is reflected in Deployment.Spec.Replicas;
  nil spec.replicas preserves an externally-set replica count across
  reconciliations (HPA-compatible contract, gated on status.observedGeneration).

E2E tests (real Kind cluster — test/e2e/thv-operator/virtualmcp/):

• virtualmcpserver_scaling_test.go: two ordered contexts covering the full
  cluster-level lifecycle:
  • Static: replicas=2 at creation → 2 ready pods, SessionStorageWarning
    condition set.
  • Scale lifecycle (1→2→1): Deployment replicas update in-place, 2 pods come
    up, SessionStorageWarning fires on scale-up and clears on scale-down.

Fixes #4220

Type of change

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

Test plan

• Unit tests (task test)
• Integration tests (task operator-test-integration)
• E2E tests (task thv-operator-e2e-test-run)
• Linting (task lint-fix)

Does this introduce a user-facing change?

No.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.49%. Comparing base (75bb444) to head (2d549d7).

Additional details and impacted files

@@              Coverage Diff               @@
##           issue-4214    #4388      +/-   ##
==============================================
+ Coverage       69.46%   69.49%   +0.03%     
==============================================
  Files             485      485              
  Lines           49814    49585     -229     
==============================================
- Hits            34604    34460     -144     
+ Misses          12530    12457      -73     
+ Partials         2680     2668      -12     

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[Copilot]

Pull request overview

Adds automated coverage around horizontal scaling behaviors in the ToolHive operator, focusing on VirtualMCPServer session storage configuration and Redis password injection, plus integration/e2e coverage for replica behavior and RunConfig scaling fields.

Changes:

• Added VirtualMCPServer e2e scenario coverage for scaling (replicas 1↔2) and SessionStorageWarning condition behavior.
• Added envtest integration coverage for VirtualMCPServer replica handling (explicit replicas + nil/HPA-compat behavior) and MCPServer RunConfig scaling config population.
• Added controller-level unit tests verifying vMCP ConfigMap sessionStorage YAML content and Redis password SecretKeyRef env var injection.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/e2e/thv-operator/virtualmcp/virtualmcpserver_scaling_test.go	New real-cluster e2e coverage for VMCP replica scaling and SessionStorageWarning behavior
cmd/thv-operator/test-integration/virtualmcp/virtualmcpserver_replicas_integration_test.go	New envtest integration checks for VMCP replica passthrough + HPA-compat preservation
cmd/thv-operator/test-integration/mcp-server/mcpserver_runconfig_integration_test.go	Adds integration assertions for RunConfig ScalingConfig presence/absence based on spec
cmd/thv-operator/controllers/virtualmcpserver_vmcpconfig_test.go	Adds unit test for ConfigMap YAML sessionStorage section population/omission
cmd/thv-operator/controllers/virtualmcpserver_deployment_test.go	Adds unit test ensuring Redis password is injected via SecretKeyRef env var (no plaintext)

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[jerm-dro]

question: The tests verify that the infrastructure scales correctly (replica counts, pod readiness, SessionStorageWarning conditions), but they don't send any MCP traffic through the scaled-out vMCP. Is this an intentional gap, or is cross-pod request handling planned for a follow-up?

Without a request hitting a different pod than the one that created the session, we're testing that pods exist but not that horizontal scaling actually works end-to-end. A few approaches that would demonstrate "any pod can handle any request":

• Scale to 2 with Redis, create a session via tools/list, delete the pod that handled it, then send tools/call on the same session and verify it succeeds on the surviving pod
• Scale to 0 and back to 1, then send a request — proves a completely fresh pod with no in-memory state can serve traffic
• Send N requests through the Service and verify responses come back successfully (doesn't prove session affinity, but proves all pods are functional)

No preference on which approach — just looking for something that closes the loop beyond infrastructure assertions.