diff --git a/easytier-core/Cargo.toml b/easytier-core/Cargo.toml
index ed623493..8d23387c 100644
--- a/easytier-core/Cargo.toml
+++ b/easytier-core/Cargo.toml
@@ -110,7 +110,10 @@ browser-config = ["config-write", "easytier-proto/api", "easytier-proto/json-rpc
 chacha20 = ["dep:chacha20poly1305"]
 openssl-crypto = ["dep:openssl"]
 ring-crypto = ["dep:ring"]
-wasi-crypto-offload = ["ring-crypto"]
+# The WASI host performs AEAD for the guest (easytier_host.crypto_aead_seal/open),
+# so the guest must not link a software backend: ring would emit env.ring_core_* imports
+# that the host module cannot provide.
+wasi-crypto-offload = []
 config-write = []
 endpoint-discovery = [
     "dep:http-body-util",
diff --git a/easytier-core/src/instance/config.rs b/easytier-core/src/instance/config.rs
index 4fe72848..51eb3404 100644
--- a/easytier-core/src/instance/config.rs
+++ b/easytier-core/src/instance/config.rs
@@ -92,6 +92,16 @@ impl Default for CoreInstanceHostConfig {
 }
 
 impl CoreInstanceHostConfig {
+    /// Record whether this host can serve the TCP subnet proxy from a user-space TCP stack.
+    ///
+    /// Hosts without an OS TUN device (WASI guests, sandboxes) can only forward proxied TCP
+    /// through such a stack, so they must advertise it for the proxy runtime to pick that path.
+    /// `requires_smoltcp` is sticky: once the host needs the stack it keeps needing it.
+    pub fn set_smoltcp_stack(&mut self, available: bool) {
+        self.smoltcp_available = available;
+        self.requires_smoltcp |= available;
+    }
+
     pub(crate) fn accepts_runtime_url(&self, url: &url::Url) -> bool {
         !self.ignore_unsupported_config
             || self
@@ -765,3 +775,24 @@ data_compress_algo = "Zstd"
         );
     }
 }
+
+#[cfg(test)]
+mod host_capability_tests {
+    use super::CoreInstanceHostConfig;
+
+    #[test]
+    fn set_smoltcp_stack_marks_the_host_as_capable_and_dependent() {
+        let mut config = CoreInstanceHostConfig::default();
+        config.set_smoltcp_stack(true);
+        assert!(config.smoltcp_available);
+        assert!(config.requires_smoltcp);
+    }
+
+    #[test]
+    fn set_smoltcp_stack_does_not_claim_a_missing_stack() {
+        let mut config = CoreInstanceHostConfig::default();
+        config.set_smoltcp_stack(false);
+        assert!(!config.smoltcp_available);
+        assert!(!config.requires_smoltcp);
+    }
+}
diff --git a/easytier-core/src/wasi/runtime.rs b/easytier-core/src/wasi/runtime.rs
index a3b616e4..11147ec3 100644
--- a/easytier-core/src/wasi/runtime.rs
+++ b/easytier-core/src/wasi/runtime.rs
@@ -152,6 +152,12 @@ pub(super) fn new_wasi_core_runtime(
         adapters.config.ignore_unsupported_config = true;
         adapters.config.endpoint_protocols = host_tunnel_schemes.to_vec();
     }
+    // A WASI guest has no OS TUN, so the TCP subnet proxy can only forward through the
+    // user-space stack. Advertise it whenever it is compiled in; never clear the flag, since
+    // the host-tunnel mode above may rely on it independently of this feature.
+    if cfg!(feature = "proxy-smoltcp-stack") {
+        adapters.config.set_smoltcp_stack(true);
+    }
     #[cfg(feature = "wasm-host-tunnel")]
     #[cfg(not(feature = "wasm-host-tunnel-outbound"))]
     let tunnel_ingress = crate::wasi::adapter::tunnel::WasiHostTunnelIngress::new(
diff --git a/script/build-wasi-core.sh b/script/build-wasi-core.sh
index c1b01a4e..57c81181 100755
--- a/script/build-wasi-core.sh
+++ b/script/build-wasi-core.sh
@@ -10,7 +10,10 @@ cd "$repository_root"
 readonly target_dir="${CARGO_TARGET_DIR:-target}"
 readonly raw_artifact="${target_dir}/wasm32-wasip1/release/easytier_core.wasm"
 readonly artifact="${target_dir}/wasm32-wasip1/release/easytier_core_go_host.wasm"
-readonly core_features="management-rpc,proxy-smoltcp-stack,ring-crypto,wasi-crypto-offload"
+# The WASI host performs AEAD for the guest, and the guest has no TLS stack of its own, so the
+# default feature set (endpoint-discovery -> rustls -> ring) must stay off: ring compiles C
+# shims into wasm32-wasip1 that become env.ring_core_* imports, which the Go host cannot provide.
+readonly core_features="management,proxy-smoltcp-stack,wasi-crypto-offload,aes-gcm,tcp-hole-punch"
 
 sha256_file() {
     if command -v sha256sum >/dev/null; then
@@ -120,6 +123,7 @@ if [[ "$version" != *"version ${binaryen_version} "* ]]; then
 fi
 
 cargo build --release --target wasm32-wasip1 -p easytier-core \
+    --no-default-features \
     --features "$core_features"
 
 optimized="${artifact}.wasm-opt.$$"