The UXP developer tool isn't saving the source... at least not to disk

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I’m writing a plug-in for InDesign, but I keep losing my JS code changes when ID crashes.

But in the editor, the code is marked as dirty when I make changes; and then that’s cleared when I “save” it. But if I look at the JS file on disk (using the dev tool’s “Open folder” command), it doesn’t contain my changes.

There’s no “show in Explorer” option in the context menu in the left pane of the UXP tool, and “Copy link address” doesn’t work; it just copies the filename, not the path. And the “Filesystem” tab is useless: It contains nothing, and the “add folder to workspace” button does nothing.

So… WTH?