Function call

src/tools/FileReadTool/FileReadTool.ts:496–651

(
    { file_path, offset = 1, limit = undefined, pages },
    context,
    _canUseTool?,
    parentMessage?,
  )

    return { result: true }
  },
  async call(
    { file_path, offset = 1, limit = undefined, pages },
    context,
    _canUseTool?,
    parentMessage?,
  ) {
    const { readFileState, fileReadingLimits } = context

    const defaults = getDefaultFileReadingLimits()
    const maxSizeBytes =
      fileReadingLimits?.maxSizeBytes ?? defaults.maxSizeBytes
    const maxTokens = fileReadingLimits?.maxTokens ?? defaults.maxTokens

    // Telemetry: track when callers override default read limits.
    // Only fires on override (low volume) — event count = override frequency.
    if (fileReadingLimits !== undefined) {
      logEvent('tengu_file_read_limits_override', {
        hasMaxTokens: fileReadingLimits.maxTokens !== undefined,
        hasMaxSizeBytes: fileReadingLimits.maxSizeBytes !== undefined,
      })
    }

    const ext = path.extname(file_path).toLowerCase().slice(1)
    // Use expandPath for consistent path normalization with FileEditTool/FileWriteTool
    // (especially handles whitespace trimming and Windows path separators)
    const fullFilePath = expandPath(file_path)

    // Dedup: if we've already read this exact range and the file hasn't
    // changed on disk, return a stub instead of re-sending the full content.
    // The earlier Read tool_result is still in context — two full copies
    // waste cache_creation tokens on every subsequent turn. BQ proxy shows
    // ~18% of Read calls are same-file collisions (up to 2.64% of fleet
    // cache_creation). Only applies to text/notebook reads — images/PDFs
    // aren't cached in readFileState so won't match here.
    //
    // Ant soak: 1,734 dedup hits in 2h, no Read error regression.
    // Killswitch pattern: GB can disable if the stub message confuses
    // the model externally.
    // 3P default: killswitch off = dedup enabled. Client-side only — no
    // server support needed, safe for Bedrock/Vertex/Foundry.
    const dedupKillswitch = getFeatureValue_CACHED_MAY_BE_STALE(
      'tengu_read_dedup_killswitch',
      false,
    )
    const existingState = dedupKillswitch
      ? undefined
      : readFileState.get(fullFilePath)
    // Only dedup entries that came from a prior Read (offset is always set
    // by Read). Edit/Write store offset=undefined — their readFileState
    // entry reflects post-edit mtime, so deduping against it would wrongly
    // point the model at the pre-edit Read content.
    if (
      existingState &&
      !existingState.isPartialView &&
      existingState.offset !== undefined
    ) {
      const rangeMatch =
        existingState.offset === offset && existingState.limit === limit