This feature exists in LucidChart or Whimsical if I recall and it essentially avoids having to repeat yourself every time you need to stay in a current tool mode. For example, I just laid out a sitemap but now need to link via the Connector tool. I have to click the Connector or use the shortcut, drag my line, then click the Connector tool again. Double-clicking the tool to lock the selected tool would be a huge improvement.
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