fix(model): report why a backend state directory fails

process.New applies its options and discards the error they return. When
WithTemporaryStateDir could not create a directory, StateDir stayed
empty and every later option went unapplied, so the failure surfaced
from Run as "mkdir : no such file or directory" naming no path.

That message cost a full day of diagnosis on a worker whose volume was
full: the real errno was ENOSPC and nothing reported it.

The loader now creates the directory itself and returns the underlying
error with the path attached.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Assisted-by: Claude Code:claude-opus-5 [golangci-lint]

pkg/model/process.go

@@ -231,6 +231,16 @@ func (ml *ModelLoader) StartProcess(grpcProcess, id string, serverAddress string
 	return ml.startProcess(grpcProcess, id, serverAddress, args...)
 }
 
+// newProcessStateDir creates the directory a backend process uses for its pid,
+// state and log files, and reports why when it cannot.
+func newProcessStateDir() (string, error) {
+	dir, err := os.MkdirTemp(os.TempDir(), "go-processmanager")
+	if err != nil {
+		return "", fmt.Errorf("creating backend process state directory under %s: %w", os.TempDir(), err)
+	}
+	return dir, nil
+}
+
 func (ml *ModelLoader) startProcess(grpcProcess, id string, serverAddress string, args ...string) (*process.Process, error) {
 	// Make sure the process is executable
 	// Check first if it has executable permissions
@@ -261,8 +271,19 @@ func (ml *ModelLoader) startProcess(grpcProcess, id string, serverAddress string
 	// and the GPU would silently fall back to CPU). No-op for other backends.
 	env = append(env, vulkanICDEnv(workDir)...)
 
+	// Resolve the state directory here rather than through
+	// process.WithTemporaryStateDir(). process.New applies its options but
+	// discards the error they return, so a temp directory that cannot be
+	// created leaves StateDir empty and every later option unapplied. Run()
+	// then reported "mkdir : no such file or directory" with no path, hiding
+	// the real cause (a full volume, or a TMPDIR that no longer resolves).
+	stateDir, err := newProcessStateDir()
+	if err != nil {
+		return nil, err
+	}
+
 	grpcControlProcess := process.New(
-		process.WithTemporaryStateDir(),
+		process.WithStateDir(stateDir),
 		process.WithName(filepath.Base(grpcProcess)),
 		process.WithArgs(append(args, []string{"--addr", serverAddress}...)...),
 		process.WithEnvironment(env...),

pkg/model/process_statedir_test.go

@@ -0,0 +1,38 @@
+package model
+
+import (
+	"os"
+	"path/filepath"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Backend process state directory", func() {
+	It("reports why the state directory could not be created", func() {
+		// A worker whose volume is full, or whose TMPDIR no longer resolves,
+		// cannot get a state directory. go-processmanager's New() drops the
+		// option error, leaving StateDir empty, and Run() then failed with
+		// "mkdir : no such file or directory" naming no path at all. Resolving
+		// the directory here keeps the real cause attached.
+		GinkgoT().Setenv("TMPDIR", filepath.Join(GinkgoT().TempDir(), "does-not-exist"))
+
+		dir, err := newProcessStateDir()
+		Expect(err).To(HaveOccurred())
+		Expect(dir).To(BeEmpty())
+		Expect(err.Error()).To(ContainSubstring("backend process state directory"))
+		Expect(err.Error()).To(ContainSubstring("does-not-exist"),
+			"the error must name the directory it could not create")
+	})
+
+	It("returns a usable directory when the temp location works", func() {
+		GinkgoT().Setenv("TMPDIR", GinkgoT().TempDir())
+
+		dir, err := newProcessStateDir()
+		Expect(err).ToNot(HaveOccurred())
+		Expect(dir).ToNot(BeEmpty())
+		info, statErr := os.Stat(dir)
+		Expect(statErr).ToNot(HaveOccurred())
+		Expect(info.IsDir()).To(BeTrue())
+	})
+})