Avoid rebuilding byte-identical source graphs

scripts/test_dependency_invalidation.sh

@@ -69,6 +69,18 @@ if [[ "$(http_marker)" != *"dependency-marker-a"* ]]; then
 	exit 1
 fi
 
+# The load-graph signature is content-addressed. A byte-identical dependency
+# touch must invalidate stat caches without recompiling its parent artifact.
+parent_wasm="$cache_dir/parent.uce.wasm"
+parent_wasm_identity=$(stat -c '%y:%s' "$parent_wasm")
+sleep 1.1
+touch "$source_dir/child.uce"
+assert_marker parent dependency-marker-a
+if [[ "$(stat -c '%y:%s' "$parent_wasm")" != "$parent_wasm_identity" ]]; then
+	echo "byte-identical dependency touch recompiled the parent artifact" >&2
+	exit 1
+fi
+
 printf '%s\n' 'CLI(Request& context) { print("readable-source-marker"); }' >"$source_dir/unreadable.uce"
 chmod 000 "$source_dir/unreadable.uce"
 if unreadable_output=$(scripts/uce-cli --get "/$test_name/unreadable.uce" __uce_expected_source_read_failure=1 2>&1); then
@@ -112,7 +124,6 @@ assert_marker parent dependency-marker-b
 # A proactive rebuild owns these same per-unit locks. While it publishes fresh
 # artifacts, requests must use the last complete artifacts instead of waiting
 # across the transitive graph. Atomic publication keeps those artifacts safe.
-parent_wasm="$cache_dir/parent.uce.wasm"
 child_wasm="$cache_dir/child.uce.wasm"
 (
 	exec 8>"$parent_wasm.lock"