fix: preserve original filename when using --front-matter (#2613)

When using --front-matter, yq creates a temporary file for the
extracted YAML content but replaces the original filename in args
with the temp file path. This caused the 'filename' operator to
return the temp file path instead of the original filename.

Added a filename alias mechanism: when front matter processing
replaces the file path, it registers the original filename as an
alias. The readDocuments and stream evaluator functions resolve
aliases before setting candidateNode.filename.

Fixes #2538

Co-authored-by: cobyfrombrooklyn-bot <cobyfrombrooklyn@gmail.com>

pkg/yqlib/front_matter_test.go

@@ -108,6 +108,55 @@ yaml: doc
 	fmHandler.CleanUp()
 }
 
+func TestFrontMatterFilenamePreserved(t *testing.T) {
+	// Regression test for https://github.com/mikefarah/yq/issues/2538
+	// When using --front-matter, the filename operator should return
+	// the original filename, not the path to the temporary file.
+	file := createTestFile(`---
+name: john
+---
+Some content
+`)
+	originalFilename := "/path/to/original/file.md"
+
+	fmHandler := NewFrontMatterHandler(file)
+	err := fmHandler.Split()
+	if err != nil {
+		panic(err)
+	}
+
+	tempFilename := fmHandler.GetYamlFrontMatterFilename()
+
+	// Register the alias (as the command code does)
+	SetFilenameAlias(tempFilename, originalFilename)
+	defer ClearFilenameAliases()
+
+	// Verify resolveFilename returns the original name
+	resolved := resolveFilename(tempFilename)
+	test.AssertResult(t, originalFilename, resolved)
+
+	// Read documents using the temp file, verify they get the original filename
+	reader, err := readStream(tempFilename)
+	if err != nil {
+		panic(err)
+	}
+	decoder := NewYamlDecoder(ConfiguredYamlPreferences)
+	docs, err := readDocuments(reader, tempFilename, 0, decoder)
+	if err != nil {
+		panic(err)
+	}
+
+	if docs.Len() == 0 {
+		t.Fatal("expected at least one document")
+	}
+
+	firstDoc := docs.Front().Value.(*CandidateNode)
+	test.AssertResult(t, originalFilename, firstDoc.filename)
+
+	tryRemoveTempFile(file)
+	fmHandler.CleanUp()
+}
+
 func TestFrontMatterSplitWithArray(t *testing.T) {
 	file := createTestFile(`[1,2,3]
 ---