fix(kserve): a GPU pool at scale-to-zero can be served — the fit check answers without a node and load proceeds

[teemow]

Problem

On gazelle the GPU pool gpu-l4 (cluster-manager, Karpenter, scale-to-zero) had no node, and model-manager refused to serve the first model on it (#90, seen in giantswarm/giantswarm#37714):

check_fit {backend: kserve, preset: qwen3-4b-instruct} → fits: false,
reason: "no eligible node: ip-10-0-164-72…: outside the serving node selector (giantswarm.io/machine-pool=gazelle-gpu-l4); …"

fitCheck needs a node matching the pool selector; with none, Fits is false and Load / Pull return ErrUnfit — but the pending predictor is exactly what makes the autoscaler launch the node. The pool could only be used once something else had scaled it up.

Solution

When the discovery's spec.gpuPool.nodeSelector names a pool no node belongs to yet, and no explicit node was asked for, the fit check answers fits: true with no node, budgetSource: pool-scale-from-zero and a reason that says the pool scales from zero and the fit against its accelerator is unverified. Load and Pull proceed without a node pin: the predictor / download Job carry the pool's toleration and selector (scheduling.go), go Pending, and Karpenter brings the node. Unchanged: an explicit node outside the pool, a pool whose nodes exist but do not fit, and no pool selector at all (no accelerator node).

TestFitCheckPoolScalesFromZero: pool selector set, no pool node → fits without a node; explicit node → refused; Load creates the serving object without a node pin; once a pool node exists the fit is against that node again. CHANGELOG.

Verification

• go test ./... -count=1: every package ok (kserve 2.5 s). golangci-lint run: 0 issues.
• Live cause read on gazelle: the check_fit answer above with the pool at 0 nodes and the discovery ConfigMap's gpuPool.nodeSelector in effect.

Plan bumblebee-plans#46 (D5/D10), epic giantswarm/giantswarm#37639.

Fixes #90.

[circleci-architect]

Published Helm chart model-manager

0.23.3-dev.kserve-poo--e-from-zero.2026-09-16.14-12-23.ha3972ae

Chart	model-manager
Version	0.23.3-dev.kserve-poo--e-from-zero.2026-09-16.14-12-23.ha3972ae
OCI reference	oci://gsoci.azurecr.io/charts/giantswarm/model-manager:0.23.3-dev.kserve-poo--e-from-zero.2026-09-16.14-12-23.ha3972ae
Digest	sha256:6ad72a0f81f0f9860f1dc94bc0f1c4b90250c09650ebab12303874f299025c67
Registry	public — gsoci.azurecr.io
Git catalog	giantswarm-test-catalog (index)

Pull this chart

helm pull oci://gsoci.azurecr.io/charts/giantswarm/model-manager --version 0.23.3-dev.kserve-poo--e-from-zero.2026-09-16.14-12-23.ha3972ae

_{Posted by architect-orb · build 1230 · commit a3972ae · updated in place on every push}