The DateTime class from luxon is used here but it is not imported in this file. This will cause a ReferenceError at runtime.

The condition directory === directory is a tautology because the parameter directory shadows the outer scope variable of the same name. This makes the subsequent code on line 178 unreachable. You should rename the parameter or use a different check to determine if the requested directory matches the current one.

    if (!directory || directory === current()[0].path.directory) return current()

The keepMounted logic currently only preserves the last row of the active turn. Since a turn can consist of multiple rows (UserMessage, multiple AssistantParts, Thinking, etc.), scrolling up while a turn is active might cause earlier parts of the streaming response to be unmounted by the virtualizer. This can disrupt the streaming experience and stateful animations like TextReveal. It is recommended to keep all rows associated with the active userMessageID mounted.

  const keepMounted = createMemo(() => {
    const id = activeMessageID()
    if (!id) return
    const rows = timelineRows()
    const indices: number[] = []
    rows.forEach((row, index) => {
      if ("userMessageID" in row && row.userMessageID === id) {
        indices.push(index)
      }
    })
    return indices.length > 0 ? indices : undefined
  })

Setting aria-hidden to true while the turn is busy prevents screen readers from accessing the assistant's response as it streams in. This significantly degrades the experience for users relying on assistive technologies. Consider removing this attribute or using aria-live to announce updates.

The toolOpen store persists state for the lifetime of the MessageTimeline component. When switching between sessions, this state is not cleared, which could lead to incorrect expanded/collapsed states if part IDs happen to collide or simply unnecessary memory growth. Consider clearing this store when the sessionKey changes.