Add WASM ECIES test for subxt-signer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hitchho

signer/tests/wasm/Cargo.lock

@@ -17,6 +17,7 @@ subxt-signer = { path = "../../", default-features = false, features = [
     "web",
     "sr25519",
     "ecdsa",
+    "ecies",
     "unstable-eth",
     "std",
 ] }

signer/tests/wasm/Cargo.toml

@@ -29,6 +29,27 @@ async fn wasm_sr25519_signing_works() {
     ));
 }
 
+#[wasm_bindgen_test]
+async fn wasm_sr25519_ecies_works() {
+    let alice = sr25519::dev::alice();
+    let bob = sr25519::dev::bob();
+
+    let plaintext = b"hello from wasm";
+    let ctx = b"wasm-ecies-test";
+
+    let encrypted = alice.encrypt(plaintext, &bob.public_key(), ctx)
+        .expect("encryption failed");
+    let decrypted = bob.decrypt(&encrypted, ctx)
+        .expect("decryption failed");
+
+    assert_eq!(&decrypted[..], plaintext);
+
+    // Wrong key should fail
+    assert!(alice.decrypt(&encrypted, ctx).is_err());
+    // Wrong context should fail
+    assert!(bob.decrypt(&encrypted, b"wrong-ctx").is_err());
+}
+
 #[wasm_bindgen_test]
 async fn wasm_ecdsa_signing_works() {
     let alice = ecdsa::dev::alice();