fix(core): keep workspace runtime available

tools/tht/internal/modelprojection/projection.go

@@ -140,7 +140,8 @@ func Render(installation config.Installation) (map[string][]byte, error) {
 	}, nil
 }
 
-// Generate publishes all adapters as one directory generation. A failed replacement restores the
+// Generate publishes all adapters as one directory generation. An unchanged generation stays in
+// place so active file bind mounts keep their source identity. 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)
@@ -152,6 +153,17 @@ func Generate(installation config.Installation) error {
 	if err := os.MkdirAll(parent, 0o755); err != nil {
 		return fmt.Errorf("create model projection parent: %w", err)
 	}
+	info, statErr := os.Lstat(target)
+	if statErr == nil {
+		if !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {
+			return fmt.Errorf("current model projection path is not a regular directory")
+		}
+		if projectionMatches(target, artifacts) {
+			return nil
+		}
+	} else if !os.IsNotExist(statErr) {
+		return fmt.Errorf("inspect current model projection generation: %w", statErr)
+	}
 	candidate, err := os.MkdirTemp(parent, ".model-projections-candidate-*")
 	if err != nil {
 		return fmt.Errorf("create model projection candidate: %w", err)
@@ -161,19 +173,12 @@ func Generate(installation config.Installation) error {
 		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)
@@ -191,6 +196,21 @@ func Generate(installation config.Installation) error {
 	return nil
 }
 
+func projectionMatches(directory string, artifacts map[string][]byte) bool {
+	for _, relative := range sortedArtifactPaths(artifacts) {
+		path := filepath.Join(directory, filepath.FromSlash(relative))
+		info, err := os.Lstat(path)
+		if err != nil || !info.Mode().IsRegular() {
+			return false
+		}
+		actual, err := os.ReadFile(path)
+		if err != nil || !bytes.Equal(actual, artifacts[relative]) {
+			return false
+		}
+	}
+	return true
+}
+
 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)

tools/tht/internal/modelprojection/projection_test.go

@@ -56,6 +56,50 @@ func TestRenderProducesDeterministicCatalogPiAndComposeProjections(t *testing.T)
 	}
 }
 
+func TestGenerateDoesNotReplaceUnchangedProjection(t *testing.T) {
+	installation := projectionFixture(t)
+	if err := Generate(installation); err != nil {
+		t.Fatalf("Generate() initial error = %v", err)
+	}
+	paths := []string{
+		installation.GeneratedModelCatalogPath(),
+		installation.GeneratedPiModelsPath(),
+		installation.GeneratedPiSettingsPath(),
+		installation.ModelProjectionComposePath(),
+	}
+	before := make(map[string]os.FileInfo, len(paths))
+	for _, path := range paths {
+		info, err := os.Stat(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		before[path] = info
+	}
+
+	originalRename := renameProjectionDirectory
+	t.Cleanup(func() { renameProjectionDirectory = originalRename })
+	renames := 0
+	renameProjectionDirectory = func(oldPath, newPath string) error {
+		renames++
+		return os.Rename(oldPath, newPath)
+	}
+	if err := Generate(installation); err != nil {
+		t.Fatalf("Generate() repeated error = %v", err)
+	}
+	if renames != 0 {
+		t.Fatalf("Generate() replaced an unchanged generation with %d renames", renames)
+	}
+	for _, path := range paths {
+		after, err := os.Stat(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !os.SameFile(before[path], after) {
+			t.Fatalf("Generate() replaced unchanged artifact %q", path)
+		}
+	}
+}
+
 func TestGenerateRestoresWholePreviousGenerationWhenPublishFails(t *testing.T) {
 	installation := projectionFixture(t)
 	if err := Generate(installation); err != nil {