fix: harden model catalog projections

tools/tht/internal/modelprojection/projection.go

@@ -21,6 +21,8 @@ const (
 	ComposeFile    = "compose.models.yaml"
 )
 
+var renameProjectionDirectory = os.Rename
+
 type runtimeCatalog struct {
 	SchemaVersion             int                          `json:"schemaVersion"`
 	DefaultSession            string                       `json:"defaultSession"`
@@ -87,10 +89,11 @@ func Render(installation config.Installation) (map[string][]byte, error) {
 		if model.Session == nil {
 			continue
 		}
-		enabled = append(enabled, model.ID)
 		if model.SessionAdapter == nil || model.SessionAdapter.Mode != "openai_compatible" {
+			enabled = append(enabled, model.ID)
 			continue
 		}
+		enabled = append(enabled, model.Provider+"/"+model.UpstreamModel)
 		provider := customProviders[model.Provider]
 		provider.BaseURL = model.Endpoint.BaseURL
 		provider.API = "openai-completions"
@@ -137,52 +140,84 @@ func Render(installation config.Installation) (map[string][]byte, error) {
 	}, nil
 }
 
-// Generate atomically replaces each generated adapter after the complete candidate has rendered.
+// Generate publishes all adapters as one directory generation. A failed replacement restores the
+// previous directory, so callers never observe a successfully returned mixed generation.
 func Generate(installation config.Installation) error {
 	artifacts, err := Render(installation)
 	if err != nil {
 		return err
 	}
-	paths := sortedArtifactPaths(artifacts)
-	for _, relative := range paths {
-		destination := filepath.Join(installation.GeneratedDirectory(), filepath.FromSlash(relative))
-		// The generated catalog contains references to secret environment variable names, never
-		// secret values. Core runs as an unprivileged container user and must be able to traverse
-		// the bind-mounted host directories and read the projections.
+	target := installation.GeneratedDirectory()
+	parent := filepath.Dir(target)
+	if err := os.MkdirAll(parent, 0o755); err != nil {
+		return fmt.Errorf("create model projection parent: %w", err)
+	}
+	candidate, err := os.MkdirTemp(parent, ".model-projections-candidate-*")
+	if err != nil {
+		return fmt.Errorf("create model projection candidate: %w", err)
+	}
+	defer func() { _ = os.RemoveAll(candidate) }()
+	if err := writeProjectionCandidate(candidate, artifacts); err != nil {
+		return err
+	}
+
+	info, statErr := os.Lstat(target)
+	if os.IsNotExist(statErr) {
+		if err := renameProjectionDirectory(candidate, target); err != nil {
+			return fmt.Errorf("publish model projection generation: %w", err)
+		}
+		return nil
+	}
+	if statErr != nil {
+		return fmt.Errorf("inspect current model projection generation: %w", statErr)
+	}
+	if !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {
+		return fmt.Errorf("current model projection path is not a regular directory")
+	}
+	previous, err := absentTemporaryPath(parent)
+	if err != nil {
+		return fmt.Errorf("reserve previous model projection generation: %w", err)
+	}
+	if err := renameProjectionDirectory(target, previous); err != nil {
+		return fmt.Errorf("prepare model projection generation replacement: %w", err)
+	}
+	if err := renameProjectionDirectory(candidate, target); err != nil {
+		if restoreErr := renameProjectionDirectory(previous, target); restoreErr != nil {
+			return fmt.Errorf("publish model projection generation: %v; restore previous generation: %w", err, restoreErr)
+		}
+		return fmt.Errorf("publish model projection generation: %w", err)
+	}
+	_ = os.RemoveAll(previous)
+	return nil
+}
+
+func writeProjectionCandidate(directory string, artifacts map[string][]byte) error {
+	if err := os.Chmod(directory, 0o755); err != nil {
+		return fmt.Errorf("protect model projection candidate: %w", err)
+	}
+	for _, relative := range sortedArtifactPaths(artifacts) {
+		destination := filepath.Join(directory, filepath.FromSlash(relative))
 		if err := os.MkdirAll(filepath.Dir(destination), 0o755); err != nil {
 			return fmt.Errorf("create model projection directory: %w", err)
 		}
-		if err := os.Chmod(filepath.Dir(destination), 0o755); err != nil {
-			return fmt.Errorf("protect model projection directory: %w", err)
-		}
-		temporary, err := os.CreateTemp(filepath.Dir(destination), ".projection-*")
-		if err != nil {
-			return fmt.Errorf("create model projection candidate: %w", err)
-		}
-		temporaryName := temporary.Name()
-		published := false
-		defer func() {
-			if !published {
-				_ = os.Remove(temporaryName)
-			}
-		}()
-		if err := temporary.Chmod(0o644); err == nil {
-			_, err = temporary.Write(artifacts[relative])
-		}
-		if closeErr := temporary.Close(); err == nil {
-			err = closeErr
-		}
-		if err != nil {
+		if err := os.WriteFile(destination, artifacts[relative], 0o644); err != nil {
 			return fmt.Errorf("write model projection candidate: %w", err)
 		}
-		if err := os.Rename(temporaryName, destination); err != nil {
-			return fmt.Errorf("publish model projection: %w", err)
-		}
-		published = true
 	}
 	return nil
 }
 
+func absentTemporaryPath(parent string) (string, error) {
+	path, err := os.MkdirTemp(parent, ".model-projections-previous-*")
+	if err != nil {
+		return "", err
+	}
+	if err := os.Remove(path); err != nil {
+		return "", err
+	}
+	return path, nil
+}
+
 // Check returns relative artifact names whose current bytes differ from the catalog projection.
 func Check(installation config.Installation) ([]string, error) {
 	artifacts, err := Render(installation)