diff --git a/docs/wasm-runtime-architecture.md b/docs/wasm-runtime-architecture.md
index 5292659..e2a3850 100644
--- a/docs/wasm-runtime-architecture.md
+++ b/docs/wasm-runtime-architecture.md
@@ -140,7 +140,10 @@ changing core-first, unit-load-order symbol resolution.
 Each FastCGI child initializes its process-local Wasmtime engine after fork and
 before entering the accept loop. This preserves Wasmtime's fork boundary while
 preventing the first request assigned to each worker from paying engine startup.
-Startup duration or failure is written to the service log.
+Startup duration or failure is written to the service log. The serialized core
+module lives in the configured writable cache root rather than beside the
+possibly root-owned deployed `core.wasm`; freshness still uses the deployed
+artifact's metadata.
 
 `request_perf()` reports worker module-cache hits and misses and divides a miss
 into artifact lookup, wasm read, custom-section parse, serialized-module
diff --git a/src/wasm/worker.cpp b/src/wasm/worker.cpp
index f27fe65..a2203ba 100644
--- a/src/wasm/worker.cpp
+++ b/src/wasm/worker.cpp
@@ -886,7 +886,9 @@ public:
 		if(!wasm_parse_sections(bytes, core_dylink, abi_ignored, parse_error))
 			return("core module: " + parse_error);
 
-		String core_cached_path = cached_wasm_path(cfg.core_wasm_path);
+		// Deployed runtime sources can be root-owned while workers run unprivileged.
+		// Keep the derived serialized core in the configured writable cache root.
+		String core_cached_path = path_join(cfg.cache_root, ".uce-core.cwasm");
 		String compile_error;
 		bool serialized_cache_hit = false;
 		auto compiled_or_cached = load_or_compile_cached_module(engine, core_cached_path, cfg.core_wasm_path, bytes, compile_error, serialized_cache_hit);