diff --git a/docs/consumers.md b/docs/consumers.md
index 56bd90d..afa58f7 100644
--- a/docs/consumers.md
+++ b/docs/consumers.md
@@ -91,7 +91,7 @@ Reference implementations developed here, pending upstreaming
 |---|---|---|
 | `ports/websocket` | `polymorph:websocket/connections` host module | their conformance suite 55/55 incl. TLS (`conformance/run.ts`) |
 | `ports/webcrypto` | `polymorph:webcrypto` host module (11 families; completion [#3](https://github.com/lann/deltic/issues/3)) | KATs vs their vectors + iroh exec-model integration |
-| `ports/webrtc` | `polymorph:webrtc-datachannels/connections` host module | their echo-demo component over real data channels |
+| `ports/webrtc` | `polymorph:webrtc-datachannels/connections` host module | their echo-demo component over real data channels; their full driver-ct loopback matrix (solo+pair, 37/37) runs under the upstreamed copy ([polymorph-webrtc-datachannels#149](https://github.com/polymorph-components/polymorph-webrtc-datachannels/pull/149)) |
 | `exams/iroh-endpoint` | the endpoint exit exam | 5/5: bind+identity, relay echo, WebRTC upgrade, jco#11/#13 assertions, teardown |
 | `ct-runner` | L3 runner for the polymorph-test L1 contract | golden-tested L4 JSONL; drives the websocket suite |
 | `tools/smoke-c0` | C0 smoke legs + report | legs 1–4 (`REPORT.md`) |
diff --git a/ports/webrtc/src/webrtc.ts b/ports/webrtc/src/webrtc.ts
index 10d5eba..26a153f 100644
--- a/ports/webrtc/src/webrtc.ts
+++ b/ports/webrtc/src/webrtc.ts
@@ -570,6 +570,14 @@ export class PeerConnection {
   #closeHooks = new Set<() => void>();
   // deno-lint-ignore no-explicit-any
   #ownedChannels = new Set<any>();
+  /**
+   * The `DataChannel` wrappers over `#ownedChannels`, latched closed by
+   * `close()`: the wrapper's local-close flag is the synchronous gate the
+   * WIT contract's "observed locally at once" requires, because a backend
+   * may transition the native `readyState` asynchronously (node-datachannel
+   * does — see `DataChannel.send`'s gate comment).
+   */
+  #ownedWrappers = new Set<DataChannel>();
   #stateTaken = false;
   #statePokes = new Set<() => void>();
 
@@ -653,7 +661,9 @@ export class PeerConnection {
       // deno-lint-ignore no-explicit-any
       this.#pc.addEventListener("datachannel", ({ channel }: any) => {
         this.#ownedChannels.add(channel);
-        push(new DataChannel(channel));
+        const wrapper = new DataChannel(channel);
+        this.#ownedWrappers.add(wrapper);
+        push(wrapper);
       });
     });
   }
@@ -695,7 +705,9 @@ export class PeerConnection {
     try {
       const channel = this.#pc.createDataChannel(options.label(), options.toInit());
       this.#ownedChannels.add(channel);
-      return new DataChannel(channel);
+      const wrapper = new DataChannel(channel);
+      this.#ownedWrappers.add(wrapper);
+      return wrapper;
     } catch (err) {
       throw new WitError<WebrtcError>({ tag: "other", val: String(err) });
     }
@@ -849,9 +861,15 @@ export class PeerConnection {
     this.#candidates.end();
     this.#channels.end();
     for (const poke of this.#statePokes) poke();
-    for (const channel of this.#ownedChannels) {
+    // Close the owned channels through their wrappers, so the close is
+    // observed locally at once (the wrapper latches its local-close flag
+    // and closes the native channel; `DataChannel.close` is idempotent).
+    // Gating on the native `readyState` alone is not enough: a backend may
+    // transition it asynchronously, leaving a post-close `send` a window
+    // in which it still sees `"open"`.
+    for (const wrapper of this.#ownedWrappers) {
       try {
-        channel.close();
+        wrapper.close();
       } catch {
         // Already closed.
       }
diff --git a/ports/webrtc/webrtc.test.ts b/ports/webrtc/webrtc.test.ts
index 8243aee..3ec2bda 100644
--- a/ports/webrtc/webrtc.test.ts
+++ b/ports/webrtc/webrtc.test.ts
@@ -286,6 +286,35 @@ Deno.test("loopback: close propagation + post-close error cases", NO_SANITIZE, a
   assertEquals((connErr as WitError<WebrtcError>).payload, { tag: "closed" });
 });
 
+Deno.test(
+  "loopback: peer-connection close latches its channels synchronously",
+  NO_SANITIZE,
+  async () => {
+    const { a, b } = await connectPair();
+    const chA = a.createDataChannel(new DataChannelOptions());
+    const chB = await firstIncoming(b);
+
+    // Closing the PEER CONNECTION closes its owned channels with the close
+    // observed locally at once (the WIT contract): the very first send()
+    // after close() fails `closed`, on the locally created channel and on
+    // the incoming (remote-created) one alike — regardless of how lazily
+    // the backend transitions the native readyState.
+    a.close();
+    const errA = await assertRejects(
+      () => chA.send({ tag: "string", val: "after-close" }),
+      WitError,
+    );
+    assertEquals((errA as WitError<WebrtcError>).payload, { tag: "closed" });
+
+    b.close();
+    const errB = await assertRejects(
+      () => chB.send({ tag: "string", val: "after-close" }),
+      WitError,
+    );
+    assertEquals((errB as WitError<WebrtcError>).payload, { tag: "closed" });
+  },
+);
+
 Deno.test("loopback: wait-connected resolves and is latched", NO_SANITIZE, async () => {
   const { a, b } = await connectPair();
   try {