Align Go parser backends and PDF pipeline with Python (#16676)

Ports remaining Go parser wiring and PDF backends, adds tenant-aware VLM
dispatch, aligns post-processing with Python, and adds end-to-end
pipeline coverage with a generated six-page PDF.

internal/parser/parser/pdf_parser_remote_common.go

@@ -0,0 +1,109 @@
+package parser
+
+import (
+	"fmt"
+	"strings"
+)
+
+func pdfFileMeta(filename string, pageCount int) map[string]any {
+	if pageCount < 0 {
+		pageCount = 0
+	}
+	return map[string]any{
+		"name":       filename,
+		"page_count": pageCount,
+		"outline":    []map[string]any{},
+	}
+}
+
+func pdfItemsToResult(filename string, items []map[string]any, outputFormat string, pageCount int) ParseResult {
+	if len(items) == 0 {
+		items = []map[string]any{{"text": "", "doc_type_kwd": "text"}}
+	}
+	pageCount = normalizePDFPageCount(pageCount, items)
+	switch strings.ToLower(strings.TrimSpace(outputFormat)) {
+	case "", "json":
+		return ParseResult{
+			OutputFormat: "json",
+			File:         pdfFileMeta(filename, pageCount),
+			JSON:         items,
+		}
+	case "markdown":
+		var b strings.Builder
+		for _, item := range items {
+			text, _ := item["text"].(string)
+			layout, _ := item["layout"].(string)
+			if strings.TrimSpace(text) == "" {
+				continue
+			}
+			if layout == "title" && !strings.HasPrefix(strings.TrimSpace(text), "#") {
+				b.WriteString("## ")
+			}
+			b.WriteString(text)
+			b.WriteString("\n\n")
+		}
+		return ParseResult{
+			OutputFormat: "markdown",
+			File:         pdfFileMeta(filename, pageCount),
+			Markdown:     strings.TrimRight(b.String(), "\n"),
+		}
+	default:
+		return ParseResult{Err: fmt.Errorf("parser: unsupported PDF output_format %q", outputFormat)}
+	}
+}
+
+func normalizePDFPageCount(fallback int, items []map[string]any) int {
+	if inferred := inferPDFPageCountFromItems(items); inferred > fallback {
+		return inferred
+	}
+	return fallback
+}
+
+func inferPDFPageCountFromItems(items []map[string]any) int {
+	pages := map[int]struct{}{}
+	for _, item := range items {
+		for page := range collectPDFPageNumbers(item) {
+			pages[page] = struct{}{}
+		}
+	}
+	return len(pages)
+}
+
+func collectPDFPageNumbers(raw any) map[int]struct{} {
+	pages := map[int]struct{}{}
+	var walk func(any)
+	walk = func(node any) {
+		switch v := node.(type) {
+		case map[string]any:
+			for _, key := range []string{"page_number", "page_num", "page_no", "page_index", "page_idx", "page"} {
+				if page := int(numberValue(v[key])); page > 0 {
+					pages[page] = struct{}{}
+				}
+			}
+			for _, key := range []string{"_pdf_positions", "positions"} {
+				if positions, ok := v[key].([][]any); ok {
+					for _, pos := range positions {
+						if len(pos) > 0 {
+							if page := int(numberValue(pos[0])); page > 0 {
+								pages[page] = struct{}{}
+							}
+						}
+					}
+				}
+			}
+			for _, child := range v {
+				walk(child)
+			}
+		case []any:
+			for _, child := range v {
+				walk(child)
+			}
+		case []map[string]any:
+			for _, child := range v {
+				walk(child)
+			}
+		}
+	}
+	walk(raw)
+	return pages
+}