feat(extract): add Text() dispatcher with md/txt passthrough

ingestion/internal/extract/extract.go

@@ -0,0 +1,39 @@
+// ingestion/internal/extract/extract.go
+package extract
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+// Text reads the file at path and returns its plain-text content.
+// Supported extensions: .md, .txt (passthrough), .pdf (via pdftotext).
+func Text(path string) (string, error) {
+	ext := strings.ToLower(fileExt(path))
+	switch ext {
+	case ".md", ".txt":
+		b, err := os.ReadFile(path)
+		if err != nil {
+			return "", fmt.Errorf("read %s: %w", path, err)
+		}
+		return string(b), nil
+	case ".pdf":
+		return extractPDF(path)
+	default:
+		return "", fmt.Errorf("unsupported file extension: %s", ext)
+	}
+}
+
+// fileExt returns the file extension including the dot, lowercased.
+func fileExt(path string) string {
+	for i := len(path) - 1; i >= 0; i-- {
+		if path[i] == '.' {
+			return path[i:]
+		}
+		if path[i] == '/' || path[i] == '\\' {
+			break
+		}
+	}
+	return ""
+}