docs(rules): document the token-gap marker

Companion to da790de. The previous wording said 'report the gap and
stop', which agents read as 'report the gap and substitute'. Name the
near-miss substitution explicitly and point at the marker instead.

.agents/agents/component-builder.md

@@ -28,9 +28,11 @@ You may not edit `tokens.css`, `verify.mjs`, `astro.config.mjs`, or
 
 - No raw hex, no px font sizes, no ad-hoc breakpoints. Tokens only.
 - **Never reshape CSS to slip past `check-tokens.mjs`** — e.g. the `font:`
-  shorthand to hide a px size it would catch as `font-size:`. If the token you
-  need does not exist, report the gap and stop; you may not add it yourself. See
-  `.agents/rules/gates.md`.
+  shorthand to hide a px size it would catch as `font-size:` — and never point a
+  legacy value at the nearest token that happens to exist. Both are silent
+  redesigns. Keep the true value and mark it
+  `/* token-gap: <reason>; owner design-system-keeper */`, which waives the
+  finding and queues it. You may not add tokens. See `.agents/rules/gates.md`.
 - No `client:*` unless genuinely interactive, with written justification.
 - Every ARIA attribute from the markup you replace survives. `verify.mjs`
   asserts several by name.