diff --git a/services/node-agent/index.js b/services/node-agent/index.js
index 5f48f51..722f8e3 100644
--- a/services/node-agent/index.js
+++ b/services/node-agent/index.js
@@ -29,6 +29,21 @@ const VERSION      = '1.4.0';
 // interpolated into a shell string.
 const DRIVER_VENDORS = ['blackmagic', 'aja', 'deltacast', 'ndi'];
 
+// Deltacast board-open stagger: serialize sidecar starts so only one
+// VHD_OpenBoardHandle is in flight at a time. Simultaneous opens trip a
+// kernel BufMngr OOB bug (delta_x300 v6.34.1, BufMngr.c:781). A promise
+// chain acts as a FIFO mutex; the settle delay lets the driver stabilize.
+const DELTACAST_STAGGER_MS = parseInt(process.env.DELTACAST_START_STAGGER_MS || '3500', 10);
+let _dcMutex = Promise.resolve();
+
+function acquireDeltacastSlot() {
+  let release;
+  const ticket = new Promise(r => { release = r; });
+  const prev = _dcMutex;
+  _dcMutex = prev.then(() => ticket);
+  return prev.then(() => release);
+}
+
 // Pick the host's LAN IP. Inside a bridge-mode container,
 // os.networkInterfaces() returns the container's docker-bridge IP (172.x),
 // not the host's LAN address. Two strategies:
@@ -166,6 +181,41 @@ async function handleSidecarStart(body, res) {
       HostConfig: hostConfig,
     };
 
+    // Deltacast: serialize board opens to prevent simultaneous VHD_OpenBoardHandle
+    // calls from wedging the delta_x300 BufMngr (OOB bug in v6.34.1). Acquire the
+    // slot (waits for any prior deltacast start to clear its settle delay), then
+    // start the container, then hold for DELTACAST_STAGGER_MS before releasing.
+    // Fail-open: if launch throws, the slot is still released so the next start
+    // isn't blocked forever.
+    if (sourceType === 'deltacast') {
+      const release = await acquireDeltacastSlot();
+      try {
+        const createRes = await dockerApi('POST', '/containers/create', spec);
+        if (createRes.status !== 201) {
+          return jsonResponse(res, 502, { error: 'Failed to create container', details: createRes.data });
+        }
+
+        const containerId = createRes.data.Id;
+        const _u = (env.find(e => e.startsWith('MAM_API_URL=')) || '').slice(12);
+        const _tok = env.some(e => e.startsWith('MAM_API_TOKEN=') && e.length > 14);
+        console.log(`[sidecar-start] ${containerId} image=${image} src=${sourceType} MAM_API_URL=${_u} token=${_tok} stagger=${DELTACAST_STAGGER_MS}ms`);
+        const startRes = await dockerApi('POST', `/containers/${containerId}/start`);
+        if (startRes.status !== 204) {
+          await dockerApi('DELETE', `/containers/${containerId}?force=true`).catch(() => {});
+          return jsonResponse(res, 502, { error: 'Failed to start container', details: startRes.data });
+        }
+
+        jsonResponse(res, 201, { containerId, capturePort });
+        // Hold slot for settle delay AFTER responding — client can proceed,
+        // but the next deltacast start won't begin until after the delay.
+        await new Promise(r => setTimeout(r, DELTACAST_STAGGER_MS));
+      } finally {
+        release();
+      }
+      return;
+    }
+
+    // Non-deltacast path: no stagger needed.
     const createRes = await dockerApi('POST', '/containers/create', spec);
     if (createRes.status !== 201) {
       return jsonResponse(res, 502, { error: 'Failed to create container', details: createRes.data });