Unsafe is a decision, and a decision needs a definition. A policy is the written rule that says what a blocked response looks like, so a block is a designed state instead of a crash.
About 1 min of reading
Write one policy used by every layer
Write the block shape
Before you run it, say out loud what it will print. Then open the answer.
Stamp which layer blocked
Before you run it, say out loud what it will print. Then open the answer.
Prove no secret leaks in the block
Before you run it, say out loud what it will print. Then open the answer.
The policy decides what a block means. Writing it first means every layer is built to the same definition.
The policy never explains the secret. It says a rule was applied, and it says nothing about the rule's content.
A blocked response says what was refused and what to do next. An empty response is a bug report users cannot file.
Every layer that blocks uses the same policy. Different blocks look different, and users cannot tell what happened.
The record says which layer blocked. That is what makes a fix aimed at a layer instead of aimed at a guess.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.