The construction track. Its governing rule is that every part of the system is either something you wrote or something the platform vendor already guarantees — and nothing in between.
Most candidates fail the fourth. That is the point.
Platform vendors ship networking, storage, cryptography, identity and a UI toolkit. Anything that duplicates them adds a second thing to learn and a second thing to patch.
Not marginally longer. A week saved once is not worth a dependency maintained for years.
If the upstream project stopping work becomes your emergency, you did not adopt a library — you adopted a liability with a maintainer you do not employ.
A dependency that decides how your tiers work, how your limits apply or how your data is shaped is a dependency you cannot reconfigure. That decision belongs in a key collection.
Write down every read and write the feature needs before designing a table. The key design falls out of the access patterns, never the other way round.
Identify which parts of the feature are product decisions rather than mechanics. Those become keys. Everything left over becomes code.
If a rule can be evaluated on the client from a key, it is presentation. If it must be enforced, it belongs in a function. Never both.
Before writing a conditional that encodes a product decision, move the decision into a key.