diff --git a/docs/wasm-runtime-architecture.md b/docs/wasm-runtime-architecture.md
index 77ba8e3..9108591 100644
--- a/docs/wasm-runtime-architecture.md
+++ b/docs/wasm-runtime-architecture.md
@@ -128,6 +128,9 @@ without instantiating it.
 backend is initialized and the requested artifact/handler is currently
 available. If an artifact is cold or stale, dispatch compiles it on demand via
 `get_shared_unit()` and rechecks. There is no native unit-execution fallback.
+Workers identify cached unit artifacts by nanosecond mtime, ctime, and size.
+Whole-second mtime alone is insufficient because a dependency-triggered rebuild
+can replace a wasm artifact within the same second as its prior build.
 
 ---
 
@@ -323,11 +326,13 @@ header free-functions are `inline`. The wasm backend exposes only declarations
 ## 10. Testing
 
 - **Regression gate**: `scripts/run_cli_tests.sh --include-wasm-kill` runs the
-  in-runtime CLI suite (`site/tests/cli_runner.uce`) plus the site test pages.
+  in-runtime CLI suite (`site/tests/cli_runner.uce`) plus the site test pages and
+  `scripts/test_dependency_invalidation.sh`. The latter 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.
 
 - **WebSocket end-to-end**: a headless client performs a raw WS handshake to
   `:HTTP_PORT` with path `/site/tests/websockets.ws.uce` (self-resolving
   `SCRIPT_FILENAME`) and asserts the `hello-ack` frame — exercising the full
   broker → worker → broker → client chain across process boundaries.
 
-
diff --git a/scripts/test_dependency_invalidation.sh b/scripts/test_dependency_invalidation.sh
index 25d318c..5e72b38 100755
--- a/scripts/test_dependency_invalidation.sh
+++ b/scripts/test_dependency_invalidation.sh
@@ -32,17 +32,34 @@ printf '%s\n' \
 	'CLI(Request& context) { print(dependency_cache_marker()); }' \
 	'RENDER(Request& context) { print(dependency_cache_marker()); }' >"$source_dir/parent.uce"
 
-first=$(scripts/uce-cli "/$test_name/parent.uce")
-if [[ "$first" != *dependency-marker-a* ]]; then
-	echo "dependency invalidation setup failed: $first" >&2
-	exit 1
-fi
+assert_marker() {
+	local path="$1"
+	local expected="$2"
+	local output
+	output=$(scripts/uce-cli "/$test_name/$path.uce")
+	if [[ "$output" != *"$expected"* ]]; then
+		echo "$path returned stale module; expected $expected: $output" >&2
+		exit 1
+	fi
+}
+
+assert_marker parent dependency-marker-a
 
 sed -i 's/dependency-marker-a/dependency-marker-b/' "$source_dir/child.uce"
-second=$(scripts/uce-cli "/$test_name/parent.uce")
-if [[ "$second" != *dependency-marker-b* ]]; then
-	echo "loaded dependency change did not recompile parent: $second" >&2
-	exit 1
-fi
+assert_marker parent dependency-marker-b
+
+# Warm every configured worker, then replace the artifact while retaining its
+# whole-second mtime. The worker cache must notice the nanosecond/ctime change.
+for _ in {1..16}; do assert_marker parent dependency-marker-b; done
+sed 's/dependency-marker-b/dependency-marker-c/' "$source_dir/child.uce" >"$source_dir/alternate-child.uce"
+sed 's/child.uce/alternate-child.uce/' "$source_dir/parent.uce" >"$source_dir/alternate.uce"
+assert_marker alternate dependency-marker-c
+parent_wasm="$cache_dir/parent.uce.wasm"
+alternate_wasm="$cache_dir/alternate.uce.wasm"
+parent_mtime=$(stat -c %Y "$parent_wasm")
+cp "$alternate_wasm" "$parent_wasm"
+touch -d "@$parent_mtime" "$parent_wasm"
+rm -f "$cache_dir/parent.uce.cwasm"
+for _ in {1..16}; do assert_marker parent dependency-marker-c; done
 
 echo "dependency invalidation passed"
diff --git a/src/wasm/worker.cpp b/src/wasm/worker.cpp
index 26945fa..fef30af 100644
--- a/src/wasm/worker.cpp
+++ b/src/wasm/worker.cpp
@@ -75,7 +75,9 @@ struct WasmUnitModule
 {
 	String source_path;   // absolute .uce path
 	String wasm_path;     // artifact in the unit cache
-	time_t mtime = 0;
+	u64 modified_ns = 0;
+	u64 changed_ns = 0;
+	u64 size = 0;
 	WasmDylinkInfo dylink;
 	WasmAbiInfo abi;
 	std::optional<wasmtime::Module> module;
@@ -640,13 +642,17 @@ public:
 			return(nullptr);
 		}
 		auto cached = module_cache.find(wasm_path);
-		if(cached != module_cache.end() && cached->second->mtime == st.st_mtime)
+		u64 modified_ns = (u64)st.st_mtim.tv_sec * 1000000000ull + (u64)st.st_mtim.tv_nsec;
+		u64 changed_ns = (u64)st.st_ctim.tv_sec * 1000000000ull + (u64)st.st_ctim.tv_nsec;
+		if(cached != module_cache.end() && cached->second->modified_ns == modified_ns && cached->second->changed_ns == changed_ns && cached->second->size == (u64)st.st_size)
 			return(cached->second);
 
 		auto unit = std::make_shared<WasmUnitModule>();
 		unit->source_path = source_path;
 		unit->wasm_path = wasm_path;
-		unit->mtime = st.st_mtime;
+		unit->modified_ns = modified_ns;
+		unit->changed_ns = changed_ns;
+		unit->size = (u64)st.st_size;
 		std::vector<u8> bytes;
 		if(!wasm_read_file(wasm_path, bytes))
 		{
@@ -696,7 +702,8 @@ private:
 		struct stat cached_stat;
 		if(stat(cached_path.c_str(), &cached_stat) == 0 && stat(wasm_path.c_str(), &wasm_stat) == 0)
 		{
-			if(cached_stat.st_mtime > wasm_stat.st_mtime)
+			if(cached_stat.st_mtim.tv_sec > wasm_stat.st_mtim.tv_sec ||
+				(cached_stat.st_mtim.tv_sec == wasm_stat.st_mtim.tv_sec && cached_stat.st_mtim.tv_nsec > wasm_stat.st_mtim.tv_nsec))
 			{
 				auto deserialized = wasmtime::Module::deserialize_file(engine, cached_path);
 				if(deserialized)