diff --git a/crates/perry-runtime/src/object/alloc.rs b/crates/perry-runtime/src/object/alloc.rs
index c792e8bb9..a9d2c0fa7 100644
--- a/crates/perry-runtime/src/object/alloc.rs
+++ b/crates/perry-runtime/src/object/alloc.rs
@@ -1000,6 +1000,22 @@ unsafe fn object_assign_set_string_key(
     key_ptr: *const crate::StringHeader,
     value_f64: f64,
 ) {
+    // `Object.assign(process.env, parsed)` — how `@next/env` loads `.env` files.
+    // `process.env.X` READS lower to `js_getenv` (the real environment), so a
+    // field stored on the cached env object leaves every read `undefined`: a
+    // Next.js standalone server saw NONE of its `.env` config (myairank's
+    // `DATABASE_URL` vanished, mysql2 then connected with an empty user and the
+    // MySQL handshake timed out). Route the write through the env setter so it
+    // lands where the reads look.
+    //
+    // This hook lives at the single write funnel rather than as an early exit in
+    // `js_object_assign_one`, so every source shape still flows through the
+    // decoding below: a primitive/array/proxy source is enumerated correctly,
+    // and a nullish source is skipped per spec instead of throwing.
+    if !target_is_array && crate::process::is_process_env_ptr(target as usize) {
+        crate::process::js_setenv(key_ptr, value_f64);
+        return;
+    }
     if target_is_array {
         // Routes integer-index keys to array element-set (extending length);
         // non-numeric keys fall back to the object setter.
@@ -1112,6 +1128,13 @@ unsafe fn object_assign_proxy_source(
 pub unsafe extern "C" fn js_object_assign_one(target_f64: f64, source_f64: f64) -> f64 {
     let target_f64 = js_object_assign_validate_target(target_f64);
 
+    // NOTE: a `process.env` target is handled in `object_assign_set_string_key`
+    // (the single write funnel) rather than here. An early exit at this point
+    // would have to re-implement source decoding, and the version that did got
+    // all three edge cases wrong: it cast any source pointer to `ObjectHeader`
+    // (type confusion on a string/array source) and it enumerated the source
+    // with `js_object_keys_value`, which *throws* on `null`/`undefined` instead
+    // of skipping it as the spec requires.
     let target_value = JSValue::from_bits(target_f64.to_bits());
     if !target_value.is_pointer() {
         return target_f64;
diff --git a/crates/perry-runtime/src/process.rs b/crates/perry-runtime/src/process.rs
index c7f24195c..fa80b0c35 100644
--- a/crates/perry-runtime/src/process.rs
+++ b/crates/perry-runtime/src/process.rs
@@ -33,16 +33,17 @@ pub use ipc::*;
 
 // ── env_misc re-exports (preserve `crate::process::*` paths) ────────────────
 pub use env_misc::{
-    js_getenv, js_getenv_value, js_process_abort, js_process_active_resources_info,
-    js_process_add_uncaught_exception_capture_callback, js_process_available_memory,
-    js_process_binding, js_process_chdir_jsv, js_process_constrained_memory, js_process_cpu_usage,
-    js_process_debug_end, js_process_debug_process, js_process_dlopen, js_process_emit_warning,
-    js_process_env, js_process_execve, js_process_exit, js_process_exit_code_get,
-    js_process_exit_code_set, js_process_fatal_exception, js_process_get_active_handles,
-    js_process_get_active_requests, js_process_has_uncaught_exception_capture_callback,
-    js_process_internal_kill, js_process_linked_binding, js_process_load_env_file,
-    js_process_memory_usage, js_process_open_stdin, js_process_raw_debug, js_process_really_exit,
-    js_process_ref, js_process_resource_usage, js_process_set_title,
+    is_process_env_object, is_process_env_ptr, js_getenv, js_getenv_value, js_process_abort,
+    js_process_active_resources_info, js_process_add_uncaught_exception_capture_callback,
+    js_process_available_memory, js_process_binding, js_process_chdir_jsv,
+    js_process_constrained_memory, js_process_cpu_usage, js_process_debug_end,
+    js_process_debug_process, js_process_dlopen, js_process_emit_warning, js_process_env,
+    js_process_execve, js_process_exit, js_process_exit_code_get, js_process_exit_code_set,
+    js_process_fatal_exception, js_process_get_active_handles, js_process_get_active_requests,
+    js_process_has_uncaught_exception_capture_callback, js_process_internal_kill,
+    js_process_linked_binding, js_process_load_env_file, js_process_memory_usage,
+    js_process_open_stdin, js_process_raw_debug, js_process_really_exit, js_process_ref,
+    js_process_resource_usage, js_process_set_title,
     js_process_set_uncaught_exception_capture_callback, js_process_start_profiler_idle_notifier,
     js_process_stop_profiler_idle_notifier, js_process_thread_cpu_usage, js_process_tick_callback,
     js_process_title, js_process_umask, js_process_umask_set, js_process_unref, js_removeenv,
diff --git a/crates/perry-runtime/src/process/env_misc.rs b/crates/perry-runtime/src/process/env_misc.rs
index 01759eda2..cbf0cfca5 100644
--- a/crates/perry-runtime/src/process/env_misc.rs
+++ b/crates/perry-runtime/src/process/env_misc.rs
@@ -861,6 +861,9 @@ pub extern "C" fn js_setenv(name_ptr: *const StringHeader, value: f64) {
             Ok(s) => s,
             Err(_) => return,
         };
+        if !env_name_is_settable(name) {
+            return;
+        }
 
         // Coerce value to string. js_jsvalue_to_string handles
         // numbers/booleans/null/undefined and returns a *mut StringHeader.
@@ -883,6 +886,19 @@ pub extern "C" fn js_setenv(name_ptr: *const StringHeader, value: f64) {
             Err(_) => return,
         };
         std::env::set_var(name, v_str);
+        // Keep the cached `process.env` object in step so enumeration
+        // (`Object.keys(process.env)`, `for…in`, spread) sees the new key —
+        // reads go through `js_getenv`, but enumeration walks this object.
+        let cached = CACHED_ENV.with(|c| c.get());
+        if cached != 0.0 {
+            let obj = crate::value::js_nanbox_get_pointer(cached) as *mut crate::ObjectHeader;
+            if !obj.is_null() {
+                let key = js_string_from_bytes(name.as_ptr(), name.len() as u32);
+                let val = js_string_from_bytes(v_str.as_ptr(), v_str.len() as u32);
+                let val_f64 = f64::from_bits(JSValue::string_ptr(val).bits());
+                crate::object::js_object_set_field_by_name(obj, key, val_f64);
+            }
+        }
     }
 }
 
@@ -980,11 +996,50 @@ pub extern "C" fn js_removeenv(name_ptr: *const StringHeader) {
 /// it straight to subsequent PropertyGet dispatch.
 #[no_mangle]
 pub extern "C" fn js_process_env() -> f64 {
-    use std::cell::Cell;
-    ipc::process_ipc_ensure_initialized();
-    thread_local! {
-        static CACHED_ENV: Cell<f64> = const { Cell::new(0.0) };
+    js_process_env_impl()
+}
+
+thread_local! {
+    static CACHED_ENV: std::cell::Cell<f64> = const { std::cell::Cell::new(0.0) };
+}
+
+/// Is `value` the live `process.env` object? Writes to it must reach the real
+/// environment (`js_setenv`), not just the cached field bag: `process.env.X`
+/// READS lower to `js_getenv`, so a field-only store is invisible.
+/// `Object.assign(process.env, parsed)` is how `@next/env` loads `.env` files —
+/// under Perry the keys landed in the object and every read still returned
+/// `undefined`, so a Next.js standalone server saw NONE of its `.env` config
+/// (myairank: `process.env.DATABASE_URL` undefined ⇒ mysql2 connected with an
+/// empty user/database and the MySQL handshake timed out).
+pub fn is_process_env_object(value: f64) -> bool {
+    let cached = CACHED_ENV.with(|c| c.get());
+    cached != 0.0 && cached.to_bits() == value.to_bits()
+}
+
+/// True when `addr` is the heap address of the cached `process.env` object.
+///
+/// The pointer form of [`is_process_env_object`], for call sites that have
+/// already unboxed the target (`Object.assign`'s write funnel).
+pub fn is_process_env_ptr(addr: usize) -> bool {
+    let cached = CACHED_ENV.with(|c| c.get());
+    if cached == 0.0 {
+        return false;
     }
+    crate::value::js_nanbox_get_pointer(cached) as usize == addr
+}
+
+/// `std::env::set_var` PANICS — and, being called from an `extern "C"` frame,
+/// aborts the process — when the name is empty, contains `=`, or contains a NUL
+/// byte. `Object.assign(process.env, parsed)` feeds it arbitrary object keys, so
+/// a single malformed key in a `.env` file would take the whole server down.
+/// Node accepts such an assignment silently, so skip these names rather than
+/// crash.
+fn env_name_is_settable(name: &str) -> bool {
+    !name.is_empty() && !name.contains('=') && !name.contains('\0')
+}
+
+fn js_process_env_impl() -> f64 {
+    ipc::process_ipc_ensure_initialized();
     let cached = CACHED_ENV.with(|c| c.get());
     if cached != 0.0 {
         return cached;
diff --git a/test-files/test_gap_object_assign_process_env.ts b/test-files/test_gap_object_assign_process_env.ts
new file mode 100644
index 000000000..af49e261f
--- /dev/null
+++ b/test-files/test_gap_object_assign_process_env.ts
@@ -0,0 +1,62 @@
+// `Object.assign(process.env, parsed)` — how `@next/env` (and dotenv, and most
+// config loaders) install a parsed `.env` file. `process.env` is not an ordinary
+// object: reads go through the runtime's env lookup, so keys merged in by the
+// generic object-assign path landed in a plain object that nothing ever consulted
+// and every `process.env.X` read came back `undefined`.
+
+const parsed: Record<string, string> = {
+  MY_APP_KEY: "abc123",
+  DATABASE_URL: "mysql://user:pw@localhost/db",
+};
+Object.assign(process.env, parsed);
+
+console.log("direct read    :", process.env.MY_APP_KEY);
+console.log("bracket read   :", process.env["DATABASE_URL"]);
+console.log("in operator    :", "MY_APP_KEY" in process.env);
+
+// a plain assignment must still work
+process.env.SET_DIRECTLY = "yes";
+console.log("set directly   :", process.env.SET_DIRECTLY);
+
+// assigning over an existing key
+Object.assign(process.env, { MY_APP_KEY: "overwritten" });
+console.log("overwritten    :", process.env.MY_APP_KEY);
+
+// a later read through a helper (not a direct member expression)
+function readEnv(name: string): string | undefined {
+  return process.env[name];
+}
+console.log("dynamic key    :", readEnv("DATABASE_URL"));
+
+// multi-source assign
+Object.assign(process.env, { A_ONE: "1" }, { A_TWO: "2" });
+console.log("multi-source   :", process.env.A_ONE, process.env.A_TWO);
+
+// Object.assign onto an ordinary object must be unaffected
+const plain: any = { a: 1 };
+const ret = Object.assign(plain, { b: 2 }, { c: 3 });
+console.log("plain object   :", JSON.stringify(plain), ret === plain);
+
+// A `process.env` target must not make Object.assign lose the spec's handling
+// of odd sources. The first implementation special-cased the env target at the
+// TOP of js_object_assign_one and re-implemented source decoding there, which
+// got all three of these wrong.
+
+// Nullish sources are SKIPPED, not an error (the env fast path enumerated them
+// with js_object_keys_value, which throws ToObject's TypeError).
+Object.assign(process.env, null);
+Object.assign(process.env, undefined);
+console.log("nullish source :", "ok");
+
+// A primitive source exposes index keys. The fast path cast ANY source pointer
+// to an ObjectHeader, so a string source was read through the wrong layout.
+Object.assign(process.env, "ab");
+console.log("string source  :", "ok");
+
+// std::env::set_var PANICS (and, from an extern "C" frame, ABORTS the process)
+// on a name that is empty or contains '=' or NUL. `Object.assign(process.env,
+// parsed)` feeds it arbitrary keys, so one malformed line in a .env file used
+// to take the whole server down. Node accepts these silently.
+Object.assign(process.env, { "": "empty" });
+Object.assign(process.env, { "A=B": "equals" });
+console.log("odd env keys   :", "ok");