fix(files): reject oversized reads before loading

nanobot/agent/tools/filesystem.py

@@ -237,6 +237,7 @@ class ReadFileTool(_FsTool):
     _scopes = {"core", "subagent", "memory"}
 
     _MAX_CHARS = 128_000
+    _MAX_FILE_SIZE_BYTES = 100 * 1024 * 1024
     _DEFAULT_LIMIT = 2000
     _MAX_PDF_PAGES = 20
 
@@ -290,6 +291,15 @@ class ReadFileTool(_FsTool):
             if not fp.is_file():
                 return ToolResult.error(f"Error: Not a file: {path}")
 
+            file_size = fp.stat().st_size
+            if file_size > self._MAX_FILE_SIZE_BYTES:
+                size_mib = file_size / (1024 * 1024)
+                max_mib = self._MAX_FILE_SIZE_BYTES // (1024 * 1024)
+                return ToolResult.error(
+                    f"Error: File too large to read ({size_mib:.1f} MiB). "
+                    f"Maximum is {max_mib} MiB."
+                )
+
             # PDF support
             if fp.suffix.lower() == ".pdf":
                 return self._read_pdf(fp, pages)