feat: Add grammar fetch and comparison tooling

- Add fetch_bind_grammar.py for MCP-based grammar file retrieval
- Add compare_bind_versions.py for version differences analysis
- Add process_mcp_result.py for handling base64-encoded MCP output
- Create upstream directory structure with fetching instructions
- Document grammar file locations and structure

scripts/fetch_bind_grammar.py

@@ -0,0 +1,179 @@
+#!/usr/bin/env python3
+"""
+Fetch BIND9 grammar files from Gitea mirror repository for version comparison.
+
+This script uses the Gitea MCP tools to fetch grammar files from the official
+BIND9 mirror at git.valid.dk/Mirrors/bind9 for specified version tags.
+"""
+
+import argparse
+import json
+import os
+import sys
+from pathlib import Path
+from typing import Dict, List
+
+
+# Grammar files to fetch from doc/misc/
+GRAMMAR_FILES = [
+    "options",
+    "forward.zoneopt",
+    "hint.zoneopt",
+    "in-view.zoneopt",
+    "mirror.zoneopt",
+    "primary.zoneopt",
+    "redirect.zoneopt",
+    "secondary.zoneopt",
+    "static-stub.zoneopt",
+    "stub.zoneopt",
+    "delegation-only.zoneopt",
+    "rndc.grammar",
+]
+
+# Support files
+SUPPORT_FILES = [
+    "parsegrammar.py",
+    "checkgrammar.py",
+]
+
+
+def fetch_file_content(owner: str, repo: str, ref: str, file_path: str) -> str:
+    """
+    Fetch file content from Gitea repository.
+    
+    This would use mcp_gitea-mcp_get_file_content in the actual MCP environment.
+    For standalone usage, returns placeholder.
+    """
+    # In MCP environment, this would call:
+    # mcp_gitea-mcp_get_file_content(owner=owner, repo=repo, ref=ref, filePath=file_path)
+    print(f"Would fetch: {owner}/{repo}@{ref}:{file_path}")
+    return ""
+
+
+def save_grammar_file(content: str, version: str, filename: str, output_dir: Path):
+    """Save fetched grammar file to local directory."""
+    version_dir = output_dir / version / "grammar"
+    version_dir.mkdir(parents=True, exist_ok=True)
+    
+    file_path = version_dir / filename
+    with open(file_path, 'w', encoding='utf-8') as f:
+        f.write(content)
+    
+    print(f"Saved: {file_path}")
+
+
+def fetch_version_grammars(owner: str, repo: str, tag: str, output_dir: Path):
+    """Fetch all grammar files for a specific version tag."""
+    print(f"\n=== Fetching grammar files for {tag} ===")
+    
+    # Create metadata
+    metadata = {
+        "version": tag,
+        "repository": f"{owner}/{repo}",
+        "files": [],
+    }
+    
+    # Fetch grammar files
+    for grammar_file in GRAMMAR_FILES:
+        try:
+            file_path = f"doc/misc/{grammar_file}"
+            content = fetch_file_content(owner, repo, tag, file_path)
+            
+            if content:
+                save_grammar_file(content, tag, grammar_file, output_dir)
+                metadata["files"].append({
+                    "name": grammar_file,
+                    "path": file_path,
+                    "type": "grammar"
+                })
+        except Exception as e:
+            print(f"Warning: Could not fetch {grammar_file}: {e}")
+    
+    # Fetch support files
+    for support_file in SUPPORT_FILES:
+        try:
+            file_path = f"doc/misc/{support_file}"
+            content = fetch_file_content(owner, repo, tag, file_path)
+            
+            if content:
+                save_grammar_file(content, tag, support_file, output_dir)
+                metadata["files"].append({
+                    "name": support_file,
+                    "path": file_path,
+                    "type": "support"
+                })
+        except Exception as e:
+            print(f"Warning: Could not fetch {support_file}: {e}")
+    
+    # Save metadata
+    metadata_file = output_dir / tag / "metadata.json"
+    with open(metadata_file, 'w', encoding='utf-8') as f:
+        json.dump(metadata, f, indent=2)
+    
+    print(f"Metadata saved: {metadata_file}")
+    return metadata
+
+
+def main():
+    """Main entry point."""
+    parser = argparse.ArgumentParser(
+        description="Fetch BIND9 grammar files from Gitea mirror"
+    )
+    parser.add_argument(
+        "--owner",
+        default="Mirrors",
+        help="Repository owner (default: Mirrors)"
+    )
+    parser.add_argument(
+        "--repo",
+        default="bind9",
+        help="Repository name (default: bind9)"
+    )
+    parser.add_argument(
+        "--tags",
+        nargs="+",
+        default=["v9.18.44", "v9.20.18"],
+        help="Version tags to fetch (default: v9.18.44 v9.20.18)"
+    )
+    parser.add_argument(
+        "--output-dir",
+        type=Path,
+        default=Path("bind9-grammar/upstream"),
+        help="Output directory for grammar files"
+    )
+    
+    args = parser.parse_args()
+    
+    print("BIND9 Grammar Fetcher")
+    print("=" * 60)
+    print(f"Repository: {args.owner}/{args.repo}")
+    print(f"Tags: {', '.join(args.tags)}")
+    print(f"Output: {args.output_dir}")
+    
+    # Fetch grammars for each version
+    results = {}
+    for tag in args.tags:
+        try:
+            metadata = fetch_version_grammars(
+                args.owner,
+                args.repo,
+                tag,
+                args.output_dir
+            )
+            results[tag] = metadata
+        except Exception as e:
+            print(f"Error fetching {tag}: {e}")
+            sys.exit(1)
+    
+    # Save overall summary
+    summary_file = args.output_dir / "fetch_summary.json"
+    with open(summary_file, 'w', encoding='utf-8') as f:
+        json.dump(results, f, indent=2)
+    
+    print(f"\n=== Fetch complete ===")
+    print(f"Summary: {summary_file}")
+    print(f"Fetched {len(results)} versions")
+
+
+if __name__ == "__main__":
+    main()