Recover after transient dependency compile failures

docs/wasm-runtime-architecture.md

@@ -423,6 +423,10 @@ header free-functions are `inline`. The wasm backend exposes only declarations
   placeholder-example errors. The dependency-invalidation gate changes a transitive
   `#load`, then replaces a warmed worker artifact while preserving its
   whole-second mtime to prove both compiler and worker caches invalidate it. It
+  also breaks a loaded dependency, verifies the parent compile fails, restores
+  the dependency byte-for-byte, and requires the parent to recover. Failed
+  builds persist the input signature that actually failed, so metadata from an
+  older successful artifact cannot indefinitely defer that rebuild.
   also rejects an unreadable unit without publishing a wasm artifact, restores
   its permissions and proves the next CLI request compiles it, then sends 48
   requests and asserts the observed worker PID set does not exceed

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"

src/lib/compiler.cpp

@@ -910,6 +910,7 @@ void compile_shared_unit(Request* context, SharedUnit* su)
 		String raw_messages = su->compiler_messages;
 		file_put_contents(su->compile_output_file_name, raw_messages + "\n");
 		file_put_contents(su->wasm_check_file_name, raw_messages + "\n");
+		file_put_contents(su->meta_file_name, compiler_unit_metadata_text(context, su, compiled_input_signature));
 		compiler_unlink_unit_wasm_artifacts(su);
 		compiler_record_compile_result(su, time_precise() - comp_start, false, "compile_error", raw_messages);
 		printf("%s \n", compiler_format_compile_failure(context, su, raw_messages).c_str());