diff --git a/SKILL.md b/SKILL.md
index fa80674..43bf197 100644
--- a/SKILL.md
+++ b/SKILL.md
@@ -137,6 +137,14 @@ taste:
   note, not deleted. SoA was parked at `parked/cultcache-soa`.
 - A capability the operator has needed across projects is reshaped, not
   removed, even when its current consumers are only tests.
+- **A general-purpose library is judged by what a reasonable consumer would
+  expect, not by our own call counts.** For CultLib, the consumer audit bounds
+  internal duplication and dead internals. It never licenses cutting or
+  omitting public capability. A math type that doesn't serialize, or a runtime
+  missing a sibling runtime's feature, is a gap to fill, not a cut to take.
+  When consumers each carry their own copy of something, the owner-level fix is
+  usually to add it to the library. (Operator, 2026-09-30: "just because we're
+  not using a feature doesn't mean we can cut it".)
 - Where the operator's own original code exists, it is the style bar.
 
 **Keep subtraction cuts separate from behaviour cuts,** so Soul can falsify each
diff --git a/references/changelog.md b/references/changelog.md
index 7bd8ae2..c733314 100644
--- a/references/changelog.md
+++ b/references/changelog.md
@@ -1131,3 +1131,15 @@ code path", and "such obviously unnecessary split authority should never pass a
 - The root cause was Self's own map wording, "with no shared item it equals sequential
   absorption exactly", which read as permission for a special path. Maps state the general
   rule and let the degenerate case fall out of it.
+
+## 2026-09-30: consumer audit bounds internals, not a general library's public surface
+
+- Evidence: P4 (collapse Geometry's CultVec types into CultMath) found that CultMath's `float2`,
+  `float3` and `rect` had no MessagePack support. Aetheria, StreamPixels and three Aetheria forks each
+  carried their own formatter copies. The first option offered was to stop serializing the Geometry
+  types. The operator's words: "we want all the math stuff to serialize, there's no excuse not to" and
+  "just because we're not using a feature doesn't mean we can cut it".
+- SKILL.md's subtraction section now says that for a general-purpose library (CultLib) the question is
+  what a reasonable consumer would expect. The call-count audit bounds only internal duplication.
+- The root cause was the skill's own "count real use … a surface with no consumer is parked" rule. It
+  was written for app-internal subtraction and read as licence to trim library capability.