docs(traps): the drift guard took three fixes, and the third one whitelisted the gap

Trap 12 told only the first act. The full story is the lesson: ThemeKeys.ALL excludes
the font roles by its own docstring, and the builder styles some base types directly
(RichTextLabel — which renders every line of DM prose on the creation screen). The
meta-guard written specifically to prevent a third miss contained a `continue` that
exempted exactly the gap it existed to catch.

A guard-of-a-guard with an exemption in it is not a guard.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/traps.md

@@ -219,11 +219,38 @@ variation/state pairs, so every variation added since — including all five thi
 milestone added for the creation screen — could drift from its generator with the test
 still green.
 
-**The guard:** when a guard is described as covering "every X," check that it actually
-enumerates `X.ALL` (or equivalent) rather than a literal list someone wrote down once. And
-make the failure message name the specific variation and property that drifted — a guard
-that only says "theme mismatch" does not tell the next person which of forty checks
-failed.
+**It took three fixes, and that is the actual lesson.**
+
+- **Fix 1** replaced the hardcoded three with `ThemeKeys.ALL`. Still could not fail: `ALL`,
+  *by its own docstring*, holds stylebox variations only — it deliberately excludes the six
+  **font roles**. Change a palette colour used only by a font role, skip the regen, ship a
+  stale theme, green.
+- **Fix 2** added `FONT_ROLES` and iterated both. Still could not fail: the builder also
+  styles some **base types** directly (`RichTextLabel`'s font, italics font, size and
+  colour), and those are in neither set. `RichTextLabel` is what renders every line of DM
+  prose on the creation screen.
+- **Fix 2 also added a meta-guard** — a test that walks the builder's own output and fails
+  if it styles anything that no set covers. That guard was written *specifically* to make a
+  third miss impossible. It contained this:
+
+  ```gdscript
+  if fresh.get_type_variation_base(variation) == &"":
+      continue        # a BASE type, not a variation
+  ```
+
+  **The meta-guard's one exemption was exactly the gap it existed to catch.**
+
+**The guard:** when a guard is described as covering "every X," check that it enumerates
+`X.ALL` (or equivalent) rather than a literal list someone wrote down once — and then check
+what `X.ALL` actually *contains*, because a set's name is not its contents. Make the failure
+message name the specific variation and property that drifted; a guard that only says "theme
+mismatch" does not tell the next person which of forty checks failed.
+
+**And the harder lesson: a guard-of-a-guard with an exemption in it is not a guard.** If you
+write a meta-test to prove a set is complete, every `continue` and every `if … : return` in
+it is a hole you are cutting on purpose. Assert on the exempted case instead of skipping it,
+or you have built the very thing you were trying to prevent, one level up, where nobody will
+look for it.
 
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