diff --git a/knip.config.ts b/knip.config.ts
index 38bd0acdfd..ff55bf1a00 100644
--- a/knip.config.ts
+++ b/knip.config.ts
@@ -88,7 +88,9 @@ const config: KnipConfig = {
     // the v1→v2 cut-over). Tracked by I-EXT (#12144).
     'src/extensions/core/noteNode.v2.ts',
     'src/extensions/core/rerouteNode.v2.ts',
-    'src/extensions/core/slotDefaults.v2.ts'
+    'src/extensions/core/slotDefaults.v2.ts',
+    // W6.P3.D — defineWidget+mount showcase port (D-widget-converge / A12).
+    'src/extensions/core/webcamCapture.v2.ts'
   ],
   vite: {
     config: ['vite?(.*).config.mts']
diff --git a/src/extensions/core/webcamCapture.v2.ts b/src/extensions/core/webcamCapture.v2.ts
new file mode 100644
index 0000000000..a93355a4c8
--- /dev/null
+++ b/src/extensions/core/webcamCapture.v2.ts
@@ -0,0 +1,110 @@
+/**
+ * WebcamCapture — rewritten with the v2 extension API.
+ *
+ * v1: registers the `WEBCAM` custom widget type via `getCustomWidgets()`
+ *     returning `node.addDOMWidget(name, 'WEBCAM', container)`, then a
+ *     separate `nodeCreated` reaches into `node.widgets` to wire the
+ *     capture button and `serializeValue` override.
+ *
+ * v2: registers the `WEBCAM` widget type via `defineWidget({ type, mount })`
+ *     per **Axiom A12** — the mount-lifecycle hook is the sole DOM seam.
+ *     The mount body captures `host` (and the constructed `<video>`) via
+ *     closure; there is no `widget.element` accessor on `WidgetHandle`.
+ *     Cleanup stops the camera stream when the widget is destroyed
+ *     (D-widget-converge §Clarification 1: cleanup = destruction-only).
+ *
+ * The `nodeCreated` half of the v1 extension (wiring the capture button +
+ * serializeValue override) surfaces several gaps already tracked under
+ * I-COORD.1 — see GAP comments inline.
+ */
+
+import { defineNode, defineWidget, type NodeHandle } from '@/extension-api'
+
+// ── defineWidget — Axiom A12 mount-lifecycle seam ───────────────────────────
+
+export default defineWidget({
+  name: 'Comfy.WebcamCapture.V2.Widget',
+  type: 'WEBCAM',
+
+  mount(host, ctx) {
+    const container = document.createElement('div')
+    container.style.background = 'rgba(0,0,0,0.25)'
+    container.style.textAlign = 'center'
+
+    const video = document.createElement('video')
+    video.style.height = video.style.width = '100%'
+
+    let stream: MediaStream | null = null
+
+    const loadVideo = async () => {
+      try {
+        stream = await navigator.mediaDevices.getUserMedia({
+          video: true,
+          audio: false
+        })
+        container.replaceChildren(video)
+        video.srcObject = stream
+        await video.play()
+      } catch (error) {
+        const label = document.createElement('div')
+        label.style.color = 'red'
+        label.style.overflow = 'auto'
+        label.style.maxHeight = '100%'
+        label.style.whiteSpace = 'pre-wrap'
+
+        const message = error instanceof Error ? error.message : String(error)
+        label.textContent = window.isSecureContext
+          ? `Unable to load webcam, please ensure access is granted:\n${message}`
+          : `Unable to load webcam. A secure context is required, if you are not accessing ComfyUI on localhost (127.0.0.1) you will have to enable TLS (https)\n\n${message}`
+
+        container.replaceChildren(label)
+      }
+    }
+
+    host.appendChild(container)
+    void loadVideo()
+
+    // Re-bind the video element to the new host on remount (graph ↔ app
+    // mode swap, subgraph promotion). Mount body is NOT re-invoked per
+    // D-widget-converge §Clarification 1.
+    ctx.onAfterRemount((newHost) => {
+      newHost.appendChild(container)
+    })
+
+    // Destruction-only cleanup: stop the camera stream + release tracks.
+    return () => {
+      stream?.getTracks().forEach((t) => t.stop())
+      stream = null
+      video.srcObject = null
+      container.remove()
+    }
+  }
+})
+
+// ── Companion defineNode — capture button + serializeValue wiring ──────────
+//
+// The `WebcamCapture` node-side logic still has open v2 surface gaps:
+//   GAP-2  (I-COORD.1): no type-construction `addWidget('button', …)` on
+//          NodeHandle — the v1 path adds a button programmatically inside
+//          `nodeCreated` to drive `capture()`.
+//   GAP-11 (new):       no `widget.serializeValue = async () => …` setter
+//          on WidgetHandle. The v2 path is `widget.on('beforeSerialize',
+//          e => e.setSerializedValue(…))`, but the v1 override is *async*
+//          (uploads to /upload/image and awaits the response); the
+//          `beforeSerialize` payload shape (D5) does not yet promise async
+//          resolution. Tracked separately — do not unblock here.
+// Until those land, the node-side companion stays a v1 extension. The
+// `defineNode` below is a placeholder that registers the type filter so
+// downstream tooling can correlate the v2 widget registration with the
+// node that consumes it.
+
+defineNode({
+  name: 'Comfy.WebcamCapture.V2.Node',
+  nodeTypes: ['WebcamCapture'],
+
+  nodeCreated(_node: NodeHandle) {
+    // Wiring deferred — see GAP-2 / GAP-11 above. The v1 extension's
+    // nodeCreated body remains the authoritative implementation until
+    // those gaps close.
+  }
+})