diff --git a/docs/release-control/v6/internal/subsystems/deployment-installability.md b/docs/release-control/v6/internal/subsystems/deployment-installability.md
index a8b988e5b..385dbba06 100644
--- a/docs/release-control/v6/internal/subsystems/deployment-installability.md
+++ b/docs/release-control/v6/internal/subsystems/deployment-installability.md
@@ -560,8 +560,12 @@ upgrade, update, release, or artifact-selection behavior.
    release signing, R2 upload, private-registry publication, or paid-runtime
    staging.
    Full public compilation may likewise overlap the frontend with agent and
-   MCP targets, but it must join successful frontend completion before any
-   server or control-plane target that consumes the embed directory starts.
+   MCP targets, but its matrix wait set must include only active compilation
+   children so the independent frontend child cannot be counted as a completed
+   binary task. Every matrix child must be joined successfully before the
+   compiled manifest is created, and successful frontend completion must be
+   joined before any server or control-plane target that consumes the embed
+   directory starts.
    Public and Pro server archives must use the shared canonical staging helper
    and may assemble independent target archives concurrently with a bounded
    worker count. The verified dual-SHA Pro path must stage its five archives
diff --git a/scripts/build-release-binaries.sh b/scripts/build-release-binaries.sh
index d37eb3dad..85c9bde55 100755
--- a/scripts/build-release-binaries.sh
+++ b/scripts/build-release-binaries.sh
@@ -247,12 +247,21 @@ while (( completed_tasks < total_tasks )); do
     done
 
     completed_pid=""
-    if wait -n -p completed_pid; then
+    # Restrict wait -n to compilation children. The frontend build is also a
+    # child of this shell, and an unrestricted wait can reap it as if it were
+    # one of the matrix tasks. That advances completed_tasks early, leaves one
+    # binary build unjoined, and can publish an incomplete compiled manifest.
+    if wait -n -p completed_pid "${active_pids[@]}"; then
         status=0
     else
         status=$?
     fi
-    task_record="${task_by_pid[${completed_pid}]:-unknown:}"
+    task_record="${task_by_pid[${completed_pid}]:-}"
+    if [[ -z "${task_record}" ]]; then
+        echo "Error: completed release compilation child is not in the active task set: ${completed_pid:-unknown}." >&2
+        terminate_active
+        exit 4
+    fi
     task_name="${task_record%%:*}"
     log_path="${task_record#*:}"
     remaining_pids=()
diff --git a/scripts/installtests/build_release_assets_test.go b/scripts/installtests/build_release_assets_test.go
index 0a26bc9a1..2a135ae73 100644
--- a/scripts/installtests/build_release_assets_test.go
+++ b/scripts/installtests/build_release_assets_test.go
@@ -157,6 +157,8 @@ func TestProPackagingBuildsFrontendEmbedWithoutTransferringBundle(t *testing.T)
 		`cp -a frontend-modern/dist/. "${FRONTEND_DIR}/"`,
 		`if [[ "${component}" == server || "${component}" == control-plane ]]; then`,
 		`finish_frontend`,
+		`wait -n -p completed_pid "${active_pids[@]}"`,
+		`completed release compilation child is not in the active task set`,
 		`transfer public Unified Agent binaries only`,
 	} {
 		if !strings.Contains(script, needle) {
@@ -169,6 +171,9 @@ func TestProPackagingBuildsFrontendEmbedWithoutTransferringBundle(t *testing.T)
 	    npm --prefix frontend-modern ci`) {
 		t.Fatal("Pro packaging must build the frontend embed prerequisite")
 	}
+	if strings.Contains(script, `wait -n -p completed_pid;`) {
+		t.Fatal("release compilation must not let wait -n consume the independent frontend child")
+	}
 	serverGate := strings.Index(script, `if [[ "${component}" == server || "${component}" == control-plane ]]; then`)
 	serverLaunch := strings.Index(script, `build_one "${component}" "${target}"`)
 	if serverGate < 0 || serverLaunch < 0 || serverGate > serverLaunch ||