Recover after transient dependency compile failures

scripts/test_dependency_invalidation.sh

@@ -69,6 +69,29 @@ if [[ "$(http_marker)" != *"dependency-marker-a"* ]]; then
 	exit 1
 fi
 
+# A failed parent build must remember the exact dependency graph that failed.
+# If a dependency is restored byte-for-byte to the last working source, the
+# old successful metadata must not make that transient failure permanent.
+printf '%s\n' \
+	'#ifndef UCE_DEPENDENCY_CACHE_CHILD' \
+	'#define UCE_DEPENDENCY_CACHE_CHILD' \
+	'String dependency_cache_marker() { return(deliberate_dependency_compile_failure); }' \
+	'#endif' >"$source_dir/child.uce"
+if restored_failure=$(scripts/uce-cli --get "/$test_name/parent.uce" __uce_expected_compile_failure=1 2>&1); then
+	echo "invalid dependency unexpectedly compiled: $restored_failure" >&2
+	exit 1
+fi
+if [[ "$restored_failure" != *"deliberate_dependency_compile_failure"* ]]; then
+	echo "invalid dependency did not report the expected compiler failure: $restored_failure" >&2
+	exit 1
+fi
+printf '%s\n' \
+	'#ifndef UCE_DEPENDENCY_CACHE_CHILD' \
+	'#define UCE_DEPENDENCY_CACHE_CHILD' \
+	'String dependency_cache_marker() { return("dependency-marker-a"); }' \
+	'#endif' >"$source_dir/child.uce"
+assert_marker parent dependency-marker-a
+
 # 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"