Reapply "don't require pulling stubs for cloud models" again (#14608)

* Revert "Revert "Reapply "don't require pulling stubs for cloud models"" (#14606)"

This reverts commit 39982a954e.

* fix test + do cloud lookup only when seeing cloud models

---------

Co-authored-by: ParthSareen <parth.sareen@ollama.com>

server/model_resolver.go

@@ -0,0 +1,81 @@
+package server
+
+import (
+	"github.com/ollama/ollama/internal/modelref"
+	"github.com/ollama/ollama/types/model"
+)
+
+type modelSource = modelref.ModelSource
+
+const (
+	modelSourceUnspecified modelSource = modelref.ModelSourceUnspecified
+	modelSourceLocal       modelSource = modelref.ModelSourceLocal
+	modelSourceCloud       modelSource = modelref.ModelSourceCloud
+)
+
+var (
+	errConflictingModelSource = modelref.ErrConflictingSourceSuffix
+	errModelRequired          = modelref.ErrModelRequired
+)
+
+type parsedModelRef struct {
+	// Original is the caller-provided model string before source parsing.
+	// Example: "gpt-oss:20b:cloud".
+	Original string
+	// Base is the model string after source suffix normalization.
+	// Example: "gpt-oss:20b:cloud" -> "gpt-oss:20b".
+	Base string
+	// Name is Base parsed as a fully-qualified model.Name with defaults applied.
+	// Example: "registry.ollama.ai/library/gpt-oss:20b".
+	Name model.Name
+	// Source captures explicit source intent from the original input.
+	// Example: "gpt-oss:20b:cloud" -> modelSourceCloud.
+	Source modelSource
+}
+
+func parseAndValidateModelRef(raw string) (parsedModelRef, error) {
+	var zero parsedModelRef
+
+	parsed, err := modelref.ParseRef(raw)
+	if err != nil {
+		return zero, err
+	}
+
+	name := model.ParseName(parsed.Base)
+	if !name.IsValid() {
+		return zero, model.Unqualified(name)
+	}
+
+	return parsedModelRef{
+		Original: parsed.Original,
+		Base:     parsed.Base,
+		Name:     name,
+		Source:   parsed.Source,
+	}, nil
+}
+
+func parseNormalizePullModelRef(raw string) (parsedModelRef, error) {
+	var zero parsedModelRef
+
+	parsedRef, err := modelref.ParseRef(raw)
+	if err != nil {
+		return zero, err
+	}
+
+	normalizedName, _, err := modelref.NormalizePullName(raw)
+	if err != nil {
+		return zero, err
+	}
+
+	name := model.ParseName(normalizedName)
+	if !name.IsValid() {
+		return zero, model.Unqualified(name)
+	}
+
+	return parsedModelRef{
+		Original: parsedRef.Original,
+		Base:     normalizedName,
+		Name:     name,
+		Source:   parsedRef.Source,
+	}, nil
+}