diff --git a/docs/reference/expression-coverage.json b/docs/reference/expression-coverage.json
index 4d115178..229b5123 100644
--- a/docs/reference/expression-coverage.json
+++ b/docs/reference/expression-coverage.json
@@ -71096,6 +71096,13 @@
       "since": "2026-08-06"
     }
   ],
-  "gaps": [],
+  "gaps": [
+    {
+      "gap_kind": "other",
+      "reason": "ibis-sqlite's TimestampBucket has no compilation rule, so a multi-digit MA-wrapper duration string (e.g. dt.truncate('2d')) on ibis-sqlite raises a raw native OperationNotDefinedError rather than a clean BackendCapabilityError. A DURATION_MULTIPLIER-class fact for this would need a corresponding class-backed OptionCell, which the 4-fixture argument-type matrix cannot instantiate for ibis-sqlite (same structural limit as test_option_fact_integrity.py's _MATRIX_UNREACHABLE_DIALECT_FACTS) -- see backlog item 99.",
+      "since": "2026-08-16",
+      "review_due": "2027-02-15"
+    }
+  ],
   "retired": []
 }
diff --git a/docs/reference/expression-coverage.md b/docs/reference/expression-coverage.md
index 779f2694..da4d27d8 100644
--- a/docs/reference/expression-coverage.md
+++ b/docs/reference/expression-coverage.md
@@ -591,7 +591,9 @@ Cells whose facts are all scoped (dialect / parameter / option / value-class) ha
 
 ## Known gaps
 
-None recorded.
+| Kind | Reason | Since | Review due |
+| --- | --- | --- | --- |
+| other | ibis-sqlite's TimestampBucket has no compilation rule, so a multi-digit MA-wrapper duration string (e.g. dt.truncate('2d')) on ibis-sqlite raises a raw native OperationNotDefinedError rather than a clean BackendCapabilityError. A DURATION_MULTIPLIER-class fact for this would need a corresponding class-backed OptionCell, which the 4-fixture argument-type matrix cannot instantiate for ibis-sqlite (same structural limit as test_option_fact_integrity.py's _MATRIX_UNREACHABLE_DIALECT_FACTS) -- see backlog item 99. | 2026-08-16 | 2027-02-15 |
 
 ## Retirement changelog
 
diff --git a/src/mountainash/core/capabilities/gaps.py b/src/mountainash/core/capabilities/gaps.py
index b575f921..41d5889b 100644
--- a/src/mountainash/core/capabilities/gaps.py
+++ b/src/mountainash/core/capabilities/gaps.py
@@ -6,9 +6,22 @@
 """
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
+from mountainash.core.capabilities.schema import GapKind, KnownGap
 
-if TYPE_CHECKING:
-    from mountainash.core.capabilities.schema import KnownGap
-
-KNOWN_GAPS: tuple[KnownGap, ...] = ()
+KNOWN_GAPS: tuple[KnownGap, ...] = (
+    KnownGap(
+        gap_kind=GapKind.OTHER,
+        reason=(
+            "ibis-sqlite's TimestampBucket has no compilation rule, so a "
+            "multi-digit MA-wrapper duration string (e.g. dt.truncate('2d')) "
+            "on ibis-sqlite raises a raw native OperationNotDefinedError "
+            "rather than a clean BackendCapabilityError. A "
+            "DURATION_MULTIPLIER-class fact for this would need a "
+            "corresponding class-backed OptionCell, which the 4-fixture "
+            "argument-type matrix cannot instantiate for ibis-sqlite (same "
+            "structural limit as test_option_fact_integrity.py's "
+            "_MATRIX_UNREACHABLE_DIALECT_FACTS) -- see backlog item 99."
+        ),
+        since="2026-08-16",
+    ),
+)