diff --git a/bin/commands/runs.js b/bin/commands/runs.js
index df02954a..025037ff 100644
--- a/bin/commands/runs.js
+++ b/bin/commands/runs.js
@@ -340,6 +340,11 @@ module.exports = function run(args, rawArgs) {
                 utils.setProcessHooks(data.build_id, bsConfig, bs_local, args, buildReportData);
                 if(isTestObservabilitySession) {
                   utils.setO11yProcessHooks(data.build_id, bsConfig, bs_local, args, buildReportData);
+                  // OB-10135: cache the automate build id so `stopBuildUpstream`
+                  // can include it on the obs-api buildStop payload. Enables the
+                  // synergy dashboard to call the railsApp resource-errors
+                  // endpoint in the automate id-space directly.
+                  process.env.BROWSERSTACK_AUTOMATION_BUILD_ID = data.build_id;
                 }
                 let message = `${data.message}! ${Constants.userMessages.BUILD_CREATED} with build id: ${data.build_id}`;
                 let dashboardLink = `${Constants.userMessages.VISIT_DASHBOARD} ${data.dashboard_url}`;
diff --git a/bin/testObservability/helper/helper.js b/bin/testObservability/helper/helper.js
index 9bb2a579..3e213d77 100644
--- a/bin/testObservability/helper/helper.js
+++ b/bin/testObservability/helper/helper.js
@@ -684,7 +684,12 @@ exports.stopBuildUpstream = async () => {
       };
     } else {
       const data = {
-        'stop_time': (new Date()).toISOString()
+        'stop_time': (new Date()).toISOString(),
+        // OB-10135: propagate the automate build hashed_id (cached at
+        // build-create time in runs.js) so obs-api can persist it and the
+        // synergy dashboard can call the railsApp resource-errors endpoint
+        // in the automate id-space directly.
+        'automate_build_id': process.env.BROWSERSTACK_AUTOMATION_BUILD_ID
       };
       const config = {
         headers: {