fix(sandbox): use succinct endpoint denial reason #1718

Job	Run time
Resolve PR metadata	6s
build-supervisor	-1s
build-gateway	-1s
gpu-e2e	0s
kubernetes-e2e	0s
e2e	0s
GPU E2E result	0s
Core E2E result	0s
Resolve PR metadata	8s
build-supervisor / Resolve build plan	2s
build-gateway / Resolve build plan	4s
build-supervisor / Rust sandbox (amd64) / sandbox (amd64)	2m 59s
build-supervisor / Rust sandbox (arm64) / sandbox (arm64)	3m 34s
build-gateway / Rust gateway (arm64) / gateway (arm64)	7m 58s
build-gateway / Rust gateway (amd64) / gateway (amd64)	6m 35s
build-supervisor / Build supervisor (arm64)	1m 43s
build-supervisor / Build supervisor (amd64)	1m 32s
build-supervisor / Merge supervisor manifest	1m 16s
build-gateway / Build gateway (amd64)	1m 44s
build-gateway / Build gateway (arm64)	1m 45s
gpu-e2e	0s
GPU E2E result	0s
build-gateway / Merge gateway manifest	1m 26s
kubernetes-e2e / Kubernetes E2E (Rust smoke)	9m 38s
e2e / E2E (python)	6m 52s
e2e / E2E (rust-podman)	10m 31s
e2e / E2E (rust-docker)	7m 36s
Core E2E result	2s
	1h 5m 29s

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