Wire SessionStorage into MCPRemoteProxy for HA support

[aron-muon]

Summary

When MCPRemoteProxy runs with multiple replicas behind a load balancer that doesn't preserve client-IP affinity (e.g. AWS ALB across multiple AZs), every non-initialize request fails with Session not found. The transparent proxy validates Mcp-Session-Id against pod-local in-memory state on every hop — transparent_proxy.go even calls this out:

// Guard: reject non-initialize requests with unknown session IDs.
// When multiple proxyrunner replicas share a Redis session store,
// a valid session will always be found.

The transport layer already supports a Redis-backed session store via runner.ScalingConfig.SessionRedis. MCPServer (#4368) and VirtualMCPServer (#4367) both wire it through. MCPRemoteProxy was the only one missing the symmetric work, leaving HA deployments architecturally broken.

What changed:

• Add MCPRemoteProxySpec.SessionStorage field — same SessionStorageConfig shape used by MCPServer and VirtualMCPServer.
• populateScalingConfigForRemoteProxy — write the non-sensitive Redis parameters (address/db/keyPrefix) into runner.ScalingConfig.SessionRedis.
• buildRedisPasswordEnvVarForRemoteProxy — inject THV_SESSION_REDIS_PASSWORD on the proxy Deployment via SecretKeyRef when sessionStorage.passwordRef is set, so the password never lands in the RunConfig ConfigMap. Mirrors VirtualMCPServer's buildRedisPasswordEnvVar exactly.

The change is intentionally a near-verbatim mirror of the MCPServer / VirtualMCPServer implementations to keep review easy — it's the same pattern reviewers have already accepted twice.

Type of change

• Bug fix
• New feature

Test plan

• Unit tests — go test ./cmd/thv-operator/controllers/... (4 + 4 = 8 new test cases pass; no regressions in existing MCPRemoteProxy suite)
• Build verification — go build ./...
• CRD regenerated with controller-gen v0.17.3

New tests:

• TestPopulateScalingConfigForRemoteProxy mirrors TestPopulateScalingConfig from mcpserver_runconfig_test.go. 4 cases including a serialization check that verifies the password never leaks into the RunConfig.
• TestBuildRedisPasswordEnvVarForRemoteProxy mirrors TestBuildRedisPasswordEnvVar from virtualmcpserver_deployment_test.go. 4 cases covering nil / memory / redis-no-pwd / redis-with-pwd.

API Compatibility

• This PR does not break the v1beta1 API. The added field (spec.sessionStorage) is optional and behaves identically to the existing nil case when omitted.

Changes

File	Lines	Change
cmd/thv-operator/api/v1beta1/mcpremoteproxy_types.go	+16	Add SessionStorage *SessionStorageConfig with kubebuilder docs explaining the transparent_proxy session-validation requirement
cmd/thv-operator/api/v1beta1/zz_generated.deepcopy.go	+5	Generated DeepCopyInto for the new field (controller-gen v0.17.3)
cmd/thv-operator/controllers/mcpremoteproxy_runconfig.go	+28	New populateScalingConfigForRemoteProxy helper, called before runConfig is returned
cmd/thv-operator/controllers/mcpremoteproxy_deployment.go	+30	New buildRedisPasswordEnvVarForRemoteProxy + call site appending it to the proxy env
cmd/thv-operator/controllers/mcpremoteproxy_runconfig_test.go	+88	TestPopulateScalingConfigForRemoteProxy (4 cases)
cmd/thv-operator/controllers/mcpremoteproxy_deployment_test.go	+63	TestBuildRedisPasswordEnvVarForRemoteProxy (4 cases)
deploy/charts/operator-crds/files/crds/toolhive.stacklok.dev_mcpremoteproxies.yaml	+114	Generated sessionStorage subschema in CRD

Does this introduce a user-facing change?

Yes. New optional field MCPRemoteProxy.spec.sessionStorage enabling Redis-backed shared session state across replicas — required for HA when the upstream load balancer doesn't preserve client-IP affinity. Same shape as MCPServer.spec.sessionStorage so existing operators already know the pattern.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.88%. Comparing base (9211a36) to head (c52a373).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5237      +/-   ##
==========================================
+ Coverage   67.86%   67.88%   +0.02%     
==========================================
  Files         610      610              
  Lines       62522    62550      +28     
==========================================
+ Hits        42431    42465      +34     
+ Misses      16910    16902       -8     
- Partials     3181     3183       +2     

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