docs: cy.exec anti patterns

docs/source/api/commands/exec.md

@@ -5,6 +5,30 @@ comments: false
 
 Execute a system command.
 
+{% note warning 'Web Server Processes' %}
+We do NOT recommend trying to start your backend web server from within Cypress.
+
+`cy.exec()` can only run commands which eventually exit.
+
+Trying to start a web server from `cy.exec()` causes all kinds of problems because:
+
+- You have to background the process
+- You lose access to it via terminal
+- You don't have access to its `stdout` or logs
+- Every time your tests run, you'd have to work out the complexity around starting an already running web server.
+- You would likely encounter constant port conflicts
+
+**Why can't I shut down the process in an `after` hook?**
+
+Because there is no guarantee that code running in an `after` will always run.
+
+While working in the Cypress GUI you can always restart / refresh while in the middle of a test. When that happens, code in an `after` won't execute.
+
+**What should I do then?**
+
+Simple. Start your web server before running Cypress. That's it!
+{% endnote %}
+
 # Syntax
 
 ```javascript