test_that("sparse NUL text keeps the existing unknown-content diagnosis", {
  bytes <- c(charToRaw(paste(rep("CoreEngine internal device log\n", 100),
    collapse = "")), as.raw(0), charToRaw("tail"))
  path <- tempfile(fileext = ".txt")
  output <- tempfile("appusage-sparse-nul-")
  on.exit(unlink(c(path, output), recursive = TRUE), add = TRUE)
  writeBin(bytes, path)
  before <- unname(tools::md5sum(path))
  ratios <- appusage_byte_ratios(bytes)
  expect_lt(ratios$nul_byte_ratio, 0.01)
  expect_lt(ratios$control_byte_ratio, 0.20)
  expect_error(rawToChar(bytes), "embedded nul")
  result <- appusage_source_preflight(path, encoding = "UTF-8")
  expect_identical(result$status, "unknown_content")
  expect_identical(result$failure_family, "source_unknown_content")
  expect_equal(result$byte_count, length(bytes))
  expect_identical(result$nul_byte_ratio, ratios$nul_byte_ratio)
  expect_identical(result$control_byte_ratio, ratios$control_byte_ratio)
  expect_identical(as.character(result$lines),
    as.character(read_appusage_lines(path, encoding = "UTF-8")))
  expect_identical(detect_appusage_type(path), "unknown")
  summary <- read_appusage_batch(path, ids = "sparse-nul", output_dir = output,
    project_name = "Synthetic", project_id = "nul", progress = FALSE)
  expect_identical(summary$status, "error")
  expect_identical(summary$failure_family, "source_unknown_content")
  expect_identical(summary$preflight_status, "unknown_content")
  expect_match(summary$error_class, "appusage_unknown_content")
  expect_equal(summary$retry_attempt, 0L)
  expect_true(is.na(summary$data_file))
  expect_true(file.exists(summary$metadata_file))
  metadata <- jsonlite::read_json(summary$metadata_file, simplifyVector = TRUE)
  expect_identical(metadata$source$preflight$failure_family, "source_unknown_content")
  expect_equal(metadata$source$preflight$byte_count, length(bytes))
  expect_gt(metadata$source$preflight$nul_byte_ratio, 0)
  expect_identical(unname(tools::md5sum(path)), before)
})

test_that("sparse NUL valid exports match the established file-reader payload", {
  fixture <- test_path("fixtures", "line_sample.txt")
  bytes <- readBin(fixture, "raw", n = file.info(fixture)$size)
  path <- tempfile(fileext = ".txt")
  on.exit(unlink(path), add = TRUE)
  sparse <- append(bytes, as.raw(0), after = 10L)
  writeBin(sparse, path)
  result <- appusage_source_preflight(path, encoding = "UTF-8")
  expect_identical(result$status, "ok")
  expect_identical(result$selected_component, "line")
  expect_equal(result$byte_count, length(sparse))
  expect_identical(result$nul_byte_ratio, 1 / length(sparse))
  established <- read_appusage_lines(path, encoding = "UTF-8")
  expect_identical(as.character(result$lines), as.character(established))
  expected <- parse_line(established, input = "lines", source_file = "synthetic")
  actual <- parse_line(path, source_file = "synthetic", encoding = "UTF-8")
  expect_identical(actual, expected)
  first <- run_first_level_appusage(path, encoding = "UTF-8", write_cache = FALSE)
  expect_identical(first$status, "success")
  expect_identical(make_second_level_appusage(first$data, export_type = "line"),
    make_second_level_appusage(parse_line(established, input = "lines",
      source_file = basename(path)), export_type = "line"))
})

test_that("NUL cleanup follows binary gates and leaves ordinary decoding intact", {
  high <- tempfile(fileext = ".txt")
  plain <- tempfile(fileext = ".txt")
  on.exit(unlink(c(high, plain)), add = TRUE)
  writeBin(c(charToRaw(paste(rep("text", 100), collapse = "")), as.raw(rep(0, 100))), high)
  result <- appusage_source_preflight(high)
  expect_identical(result$status, "binary_control_bytes")
  expect_identical(result$failure_family, "source_binary")
  expect_identical(result$lines, character())
  writeLines("ordinary internal log", plain, useBytes = TRUE)
  result <- appusage_source_preflight(plain)
  expect_identical(result$status, "unknown_content")
  expect_identical(result$nul_byte_ratio, 0)
  expect_identical(as.character(result$lines), as.character(read_appusage_lines(plain)))
})