diff --git a/docs/superpowers/evidence/cap-artifact-growth-2026-08-23.json b/docs/superpowers/evidence/cap-artifact-growth-2026-08-23.json
new file mode 100644
index 00000000..6a2a9067
--- /dev/null
+++ b/docs/superpowers/evidence/cap-artifact-growth-2026-08-23.json
@@ -0,0 +1,37 @@
+{
+  "intent": "Stop the superpowers bookkeeping tree from silently regrowing to the 695 files that made a 655-file prune necessary, by capping it in the gate instead of leaving a note recommending it.",
+  "scope": [
+    "meta/scripts/check_repo_size.sh - adds a per-directory artifact cap",
+    "Non-goal: changing the source-file ceiling or the excluded prefixes, both unchanged."
+  ],
+  "changes": [
+    "Added ARTIFACT_DIRS + MAX_ARTIFACTS_PER_DIR=60, checked by a new check_artifact_dirs helper wired into main alongside the existing source-file ceiling.",
+    "main now accumulates failures rather than returning on the first, so a commit that trips both the source ceiling and the artifact cap reports both.",
+    "60 is the headroom the prune bought (21 files per dir today). The header says to prune rather than raise it when it fails."
+  ],
+  "verification": [
+    {
+      "command": "./meta/scripts/check_repo_size.sh",
+      "result": "pass",
+      "evidence": "'1050 source files (ceiling 1200)' EXIT=0 with evidence/contracts at 21 each, under the 60 cap. --count still prints the bare number, EXIT=0."
+    },
+    {
+      "command": "MAX_ARTIFACTS_PER_DIR=5 variant",
+      "result": "pass",
+      "evidence": "EXIT=1 listing BOTH dirs (evidence 22, contracts 21) plus the prune hint - confirms the new branch fires and that it does not stop at the first offender."
+    },
+    {
+      "command": "pre-commit run repo-size-cap --all-files; pre-commit run --files meta/scripts/check_repo_size.sh",
+      "result": "pass",
+      "evidence": "Hook Passed; shfmt and shellcheck clean on the modified script."
+    }
+  ],
+  "risks": [
+    "A legitimate burst of commits can now trip the cap and block a commit until artifacts are pruned. That is the intended trade: the previous behaviour was unbounded growth noticed only months later.",
+    "The cap counts tracked files per directory, so it does not distinguish a needed recent artifact from an old one; the operator chooses what to prune."
+  ],
+  "rollback": [
+    "git revert the commit; the source-file ceiling and all other behaviour are untouched by this change.",
+    "After rollback, confirm ./meta/scripts/check_repo_size.sh still exits 0 and prints the source count."
+  ]
+}
diff --git a/meta/scripts/check_repo_size.sh b/meta/scripts/check_repo_size.sh
index 2e5c2b8b..8da1626f 100755
--- a/meta/scripts/check_repo_size.sh
+++ b/meta/scripts/check_repo_size.sh
@@ -24,10 +24,15 @@
 # The count is always printed, so the threshold can be audited from any CI log
 # rather than being taken on trust.
 #
+# The generated trees are excluded from that count but capped separately: they
+# grow about one file per commit, which is what made a 655-file prune
+# necessary in the first place. Capping them here means the next overflow
+# fails a commit instead of being noticed months later.
+#
 #   check_repo_size.sh            # count and enforce
 #   check_repo_size.sh --count    # print the number only, always exit 0
 #
-# Exits 0 when at or under the ceiling, 1 when over.
+# Exits 0 when at or under every ceiling, 1 when over any of them.
 # ============================================================================
 
 set -euo pipefail
@@ -45,6 +50,16 @@ readonly EXCLUDED_PREFIXES=(
 	.hippo/
 )
 
+# Per-commit bookkeeping. Pruned to 20 each (plus a template) on 2026-08-23;
+# the cap is the headroom that prune bought, so the tree cannot silently
+# return to the 695 files it held before. When this fails, prune - do not
+# raise it.
+readonly ARTIFACT_DIRS=(
+	docs/superpowers/evidence
+	docs/superpowers/contracts
+)
+readonly MAX_ARTIFACTS_PER_DIR=60
+
 COUNT_ONLY=0
 
 usage() {
@@ -68,6 +83,24 @@ source_files() {
 	git ls-files | grep -v "${filter[@]}" || true
 }
 
+# Fail when a bookkeeping directory has grown past its cap. Reports every
+# offending directory rather than stopping at the first.
+check_artifact_dirs() {
+	local dir n over=0
+	for dir in "${ARTIFACT_DIRS[@]}"; do
+		n="$(git ls-files "$dir" | wc -l)"
+		if ((n > MAX_ARTIFACTS_PER_DIR)); then
+			echo "check_repo_size: $dir holds $n files, over the $MAX_ARTIFACTS_PER_DIR cap" >&2
+			over=1
+		fi
+	done
+	((over)) && {
+		echo "Prune the oldest artifacts; they stay available in git history." >&2
+		return 1
+	}
+	return 0
+}
+
 main() {
 	local count
 	count="$(source_files | wc -l)"
@@ -77,12 +110,18 @@ main() {
 		return 0
 	fi
 
+	local failed=0
+
 	if ((count > MAX_SOURCE_FILES)); then
 		echo "check_repo_size: $count source files, over the $MAX_SOURCE_FILES ceiling" >&2
 		echo "Extract a unit into its own repo rather than raising the cap." >&2
-		return 1
+		failed=1
 	fi
 
+	check_artifact_dirs || failed=1
+
+	((failed)) && return 1
+
 	echo "check_repo_size: $count source files (ceiling $MAX_SOURCE_FILES)"
 	return 0
 }