docs(v4.0.0): ACL intent -- a runtime check of a word; TTL is how often

Captain Bob, 2026-10-05.  The countdown runs on every execution; the
permission check only when it reaches zero.  A compile-time check does not
meet the intent, so a word that is to be checked must be called.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/v4.0.0/V3-PARITY.md

@@ -290,6 +290,22 @@ check it.
   give headers to. The node must be able to tell, at the call, whether the
   target has the three cells of an entry before it.
 
+**Intent, stated by Captain Bob 2026-10-05:** "Intent is for a runtime
+check of a word. And the way we were originally doing it is the TTL was how
+often the check would be performed. If the TTL was still valid, the word
+would not get checked, in order to save the overhead of checking for
+permissions every time."
+
+So: the check is at run time, per word, at the hook. The countdown is the
+cheap part, done on every execution; the permission check itself is done
+only when the countdown reaches zero. A check made only when a definition
+is compiled does not meet the intent.
+
+What follows for the in-line words: to be checked at run time a word has
+to pass through the hook, so it has to be called. The six that cannot be
+called (`>R R> R@ I J LEAVE`) are the residue: they can only appear inside
+a definition, and can only be checked when it is compiled.
+
 **And what v3 measures.** v3 works a word's TTL out from that word's heat
 (`heat/4 + 256`). Section 2.7 rules heat per opcode. A word card exactly as
 v3's needs a count per word, which the same hook could take; whether it