Dialog opened from an onMouseDown handler closes immediately (same click's mouseup hits the backdrop)

Description

Plugins that open a dialog from an onMouseDown handler get a dialog that flashes and closes instantly — the release of the same physical click dismisses it.

packages/tui/src/ui/dialog.tsx closes the full-screen backdrop on onMouseUp (onMouseDown only sets the selection dismiss flag). OpenTUI dispatches press/release as separate events and hit-tests each fresh, and the dialog mounts synchronously during the press — so the release hit-tests against the newly mounted backdrop and onClose() fires before the user can interact. There is no opt-out (dismissOnOutsideClick or similar) on Dialog / DialogSelect / dialog.replace.

Workaround: open the dialog from onMouseUp instead — works, but any element that legitimately needs to react on press can't open dialogs safely.

Steps to reproduce

1. Load a plugin that registers a bottom-bar slot and opens a dialog on press:

export const Repro = {
  id: "repro-dialog",
  tui(api) {
    api.slots.register("app_bottom", () => (
      <box onMouseDown={() => {
        const DialogSelect = api.ui.DialogSelect
        api.ui.dialog.replace(() => (
          <DialogSelect
            title="Pick one"
            options={[{ title: "A", value: "a" }, { title: "B", value: "b" }]}
            onSelect={() => api.ui.dialog.clear()}
          />
        ))
      }}>
        <text>click me</text>
      </box>
    ))
  },
}

2. Start opencode, click the bar element once.
3. The dialog appears for a frame and closes by itself.

Changing the handler to onMouseUp makes the dialog stay open — confirming it's the same click's release hitting the freshly mounted backdrop.

Suggested fix

• Ignore backdrop mouseups belonging to the press that opened the dialog (e.g. record when the stack becomes non-empty and drop the first mouseup of that sequence), or
• add a dismissOnOutsideClick opt-out on Dialog / DialogSelect for plugin use.

Happy to test a fix.

Environment

• OpenCode: 1.18.26 (npm)
• OS: Windows 11
• Terminal: Windows Terminal
• Plugins: FlashCodersRead (TUI speed-reader bar — where I hit this)