feat: complete v0.3.1 agent workflow

internal/tools/paths.go

@@ -2,22 +2,85 @@ package tools
 
 import (
 	"fmt"
+	"os"
 	"path/filepath"
 	"strings"
 )
 
 func resolvePath(baseDir, path string) (string, error) {
+	resolved, canonicalBase, err := resolveLexicalPath(baseDir, path)
+	if err != nil {
+		return "", err
+	}
+	canonical, err := filepath.EvalSymlinks(resolved)
+	if err != nil {
+		return "", err
+	}
+	if !isWithinDir(canonical, canonicalBase) {
+		return "", fmt.Errorf("path escapes the project directory through a symbolic link: %s", path)
+	}
+	return canonical, nil
+}
+
+// resolvePathForWrite resolves a path that may not exist yet while preventing
+// existing parent-directory symlinks from escaping the project directory.
+func resolvePathForWrite(baseDir, path string) (string, error) {
+	resolved, canonicalBase, err := resolveLexicalPath(baseDir, path)
+	if err != nil {
+		return "", err
+	}
+
+	existing := resolved
+	var suffix []string
+	for {
+		_, err := os.Lstat(existing)
+		if err == nil {
+			break
+		}
+		if !os.IsNotExist(err) {
+			return "", err
+		}
+		parent := filepath.Dir(existing)
+		if parent == existing {
+			return "", err
+		}
+		suffix = append(suffix, filepath.Base(existing))
+		existing = parent
+	}
+
+	canonical, err := filepath.EvalSymlinks(existing)
+	if err != nil {
+		return "", err
+	}
+	for i := len(suffix) - 1; i >= 0; i-- {
+		canonical = filepath.Join(canonical, suffix[i])
+	}
+	if !isWithinDir(canonical, canonicalBase) {
+		return "", fmt.Errorf("path escapes the project directory through a symbolic link: %s", path)
+	}
+	return canonical, nil
+}
+
+func resolveLexicalPath(baseDir, path string) (string, string, error) {
 	if path == "" {
 		path = "."
 	}
 	if filepath.IsAbs(path) {
-		return "", fmt.Errorf("absolute paths are not allowed; use a path relative to the project directory")
+		return "", "", fmt.Errorf("absolute paths are not allowed; use a path relative to the project directory")
 	}
-	resolved := filepath.Clean(filepath.Join(baseDir, path))
-	if !isWithinDir(resolved, baseDir) {
-		return "", fmt.Errorf("path escapes the project directory: %s", path)
+	absBase, err := filepath.Abs(baseDir)
+	if err != nil {
+		return "", "", err
 	}
-	return resolved, nil
+	canonicalBase, err := filepath.EvalSymlinks(absBase)
+	if err != nil {
+		return "", "", err
+	}
+	resolved := filepath.Clean(filepath.Join(absBase, path))
+	if !isWithinDir(resolved, absBase) {
+		return "", "", fmt.Errorf("path escapes the project directory: %s", path)
+	}
+	return resolved, canonicalBase, nil
 }
 
 func isWithinDir(path, dir string) bool {