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/rules/gates.md

@@ -66,16 +66,34 @@ worse than failing, because failure is visible and this is not.
 `font:` shorthand passes it. Task 07 did exactly that, in **two** components,
 with a comment saying so. Both hardcoded values survived into a "green" branch.
 
-When a token you need does not exist:
+### Do not substitute a near-miss token either
 
-1. Stop. Do not invent a value, and do not reshape the syntax to hide one.
-2. Write the gap in your task report: the selector, the legacy value(s) it comes
-   from, and which file owns the token.
-3. If your task cannot proceed without it, say so and stop. A blocked task is a
-   finding. A silently-passing one is a defect that ships.
+The second way to break this is subtler, and both tasks 10 and 11 did it: keep
+the gate happy by pointing a legacy value at the closest token that already
+exists. `#e5eeeb` became `var(--paper)`. Diff-**added** green became
+`var(--accent)` — purple. `12px` and `14px` both became `var(--step-1)`, 15px.
 
-`tokens.css` has a single owner (`design-system-keeper`) precisely so that "add
-a token" is a decision, not a side effect.
+That is a silent redesign, and it is _worse_ than leaving the raw value in,
+because a raw hex is at least honest about being unresolved.
+
+### What to do instead: mark the gap
+
+`tokens.css` has one owner (`design-system-keeper`) so that "add a token" is a
+decision, not a side effect. You may not add one. You **can** keep the true
+value and stay green — mark it:
+
+```css
+/* token-gap: no --step-* covers 12px; owner design-system-keeper */
+font-size: 12px;
+```
+
+The marker waives that one finding. It needs a real reason after the colon; a
+bare `token-gap:` is rejected. Every marked value is listed on each run, so the
+debt stays visible rather than disappearing.
+
+Write it in your task report as well: selector, legacy value, owning file.
+Marking a gap is not resolving it — it keeps the site truthful until whoever
+owns the token layer decides.
 
 ## Parallelism