ReadFileTool
Reads a text file's content, sandboxed to external storage via PathValidator. Files with an unrecognized extension are scanned for null bytes in the first 8 KB and rejected as binary if any are found. Output is truncated to the max_lines param. Requires READ_EXTERNAL_STORAGE on API ≤32; uses File API access on API 33+. Output: path, content (newline-joined lines), lines_returned, truncated.