The user who asked for a "big ol' blazing warning sign" has put their finger on a real problem, and we think the solution is simpler than they suspect. They already know how to check for external links manually, but people forget. That is not a failure of effort; it is a failure of design. When a process depends on human memory to catch an invisible error, the process will eventually break. The goal should be to make the warning automatic, not to train people to remember another step.
This is where we would point to a more modern approach. Instead of building a Power Query routine that users must run, consider a single cell formula or a tiny VBA event that fires when the workbook opens. A simple `=EXTERNAL` check wrapped in an `IF` statement can display a red banner in a locked cell. Or, for a truly unavoidable alert, a `Workbook_Open` macro can pop a message box the moment any external link exists. The user already knows the logic; they just need to shift the trigger from "user remembers to check" to "file opens and checks itself." That is the difference between a tool that fights human nature and one that works with it.
What this reveals about the broader spreadsheet landscape is that legacy tools still force users to become amateur programmers just to prevent basic data corruption. The user should not have to ask "any thoughts" about a warning sign. The software should already offer a native, toggleable alert for external links. In an AI-native spreadsheet, detecting and flagging external references would be a built-in guardrail, not a forum question. The fact that this user is engineering a workaround tells us the industry has not yet caught up to the real workflows people need.
Here is the concrete takeaway: automate the guardrail, not the reminder. If your spreadsheet cannot survive an accidental paste, then the spreadsheet itself should scream when it happens. Stop asking people to remember. Make the warning inevitable.