test: add llm-proxy agent thread e2e

[casey-brooks]

Summary

• Adds TestAgentRespondsToThreadMessageViaLLMProxy to the go-core E2E suite.
• Covers user/API token/org/provider/model/agent/thread setup, sends hi, and waits for the deterministic Hi! How are you? agent response.
• Uses the existing TestLLM endpoint and existing harness helpers; no commercial LLM keys required.
• Creates the agent and agent env with the user identity context so llm-proxy sees a user-owned API token and model authorization matches the model's organization membership.
• Related to CI: run E2E test for thread message → agent execution → response llm-proxy#57.

Tests

• nix shell nixpkgs#gcc nixpkgs#buf -c bash -c 'cd /workspace/e2e/suites/go-core && buf generate && go test -count=1 -tags "e2e svc_agents_orchestrator svc_llm_proxy" -run "TestLLMProxyURLDefaultUsesIngress|TestLLMProxyURLExplicitOverride|TestLLMGatewayConnectEndpointPath" ./tests && go test -count=1 -tags "e2e svc_agents_orchestrator svc_llm_proxy" -run "^$" ./tests && go vet -tags "e2e svc_agents_orchestrator svc_llm_proxy" ./tests'
  • e2e helper tests: 3 passed, 0 failed, 0 skipped.
  • e2e compile-only check: 0 passed, 0 failed, 0 skipped.
  • lint/vet passed with no errors.

[casey-brooks]

Test & Lint Summary

• cd /workspace/e2e/suites/go-core && go test -count=1 -tags 'e2e svc_agents_orchestrator svc_llm_proxy' -run 'TestLLMProxyURLDefaultUsesIngress|TestLLMProxyURLExplicitOverride|TestLLMGatewayConnectEndpointPath' ./tests — 3 passed, 0 failed, 0 skipped.
• cd /workspace/e2e/suites/go-core && go test -count=1 -tags 'e2e svc_agents_orchestrator svc_llm_proxy' -run '^$' ./tests — 0 passed, 0 failed, 0 skipped; compile-only check passed.
• cd /workspace/e2e/suites/go-core && go vet -tags 'e2e svc_agents_orchestrator svc_llm_proxy' ./tests — lint/vet passed with no errors.

Full TestAgentRespondsToThreadMessageViaLLMProxy execution requires in-cluster services; local direct run from this workspace failed at dialing agents:50051, as expected outside the E2E cluster.