fix: treat Nix files as readable uploads (#2249)

tests/test_nix_upload_text.py

@@ -0,0 +1,20 @@
+from src.document_processor import _is_text_file, _process_text_file
+from src.upload_handler import UploadHandler
+
+
+def test_nix_files_are_treated_as_readable_documents(tmp_path):
+    handler = UploadHandler(str(tmp_path), str(tmp_path / "uploads"))
+
+    assert handler.is_document_file("configuration.nix")
+    assert _is_text_file("configuration.nix")
+
+
+def test_nix_file_processing_includes_content_in_code_block(tmp_path):
+    nix_file = tmp_path / "configuration.nix"
+    nix_file.write_text("{ pkgs, ... }:\n{\n  services.openssh.enable = true;\n}\n", encoding="utf-8")
+
+    rendered = _process_text_file(str(nix_file))
+
+    assert "[Type: nix" in rendered
+    assert "```nix" in rendered
+    assert "services.openssh.enable = true;" in rendered