diff --git a/REQUIREMENTS.md b/REQUIREMENTS.md
index a58121e..45744b7 100644
--- a/REQUIREMENTS.md
+++ b/REQUIREMENTS.md
@@ -484,6 +484,9 @@ what a valid business email is.
 ### req: push/005
 005	Push is one-way server-to-client delivery of EffectBatch. It does not define client mutation, optimistic queues, reconciliation, or conflict handling.
 
+### req: push/006
+006	`data-slhx-sse` opens only non-empty same-origin SSE URLs by default. Empty static URLs are build errors; cross-origin streams belong to explicit integration code rather than the standard runtime convention.
+
 ---
 
 ## sync
diff --git a/slhx-build/src/lib.rs b/slhx-build/src/lib.rs
index 2e24ded..3385d0c 100644
--- a/slhx-build/src/lib.rs
+++ b/slhx-build/src/lib.rs
@@ -1041,6 +1041,14 @@ fn reject_invalid_slhx_attr_values(path: &Path, attrs: &[SurfaceAttribute]) -> i
                     "expected a non-empty confirmation message",
                 ));
             }
+            "data-slhx-sse" if value.trim().is_empty() => {
+                return Err(invalid_slhx_value(
+                    path,
+                    &attr.name,
+                    value,
+                    "expected a non-empty same-origin SSE URL",
+                ));
+            }
             "data-slhx-debounce" | "data-slhx-throttle" | "data-slhx-every"
                 if !valid_duration(value) =>
             {
@@ -1578,6 +1586,12 @@ fn main() {{
                 "data-slhx-confirm",
                 "non-empty",
             ),
+            (
+                "empty-sse",
+                r#"<section data-slhx-root="notifications" data-slhx-sse=""></section>"#,
+                "data-slhx-sse",
+                "same-origin SSE URL",
+            ),
         ] {
             let base = test_dir(&format!("slhx-build-invalid-convention-{case}-test"));
             let templates = base.join("templates");
diff --git a/slhx-js/runtime/slhx.js b/slhx-js/runtime/slhx.js
index ea684bf..f31bc19 100644
--- a/slhx-js/runtime/slhx.js
+++ b/slhx-js/runtime/slhx.js
@@ -637,7 +637,12 @@
   function bindSse(root) {
     const url = root.getAttribute("data-slhx-sse");
     if (!url || sseSources.has(root) || typeof EventSource === "undefined") return;
-    const source = new EventSource(new URL(url, location.href).href);
+    const href = new URL(url, location.href);
+    if (href.origin !== location.origin) {
+      emit(root, "slhx:sse-error", url);
+      return;
+    }
+    const source = new EventSource(href.href);
     source.addEventListener("slhx", (event) => applySseMessage(root, event));
     source.addEventListener("message", (event) => applySseMessage(root, event));
     source.addEventListener("error", () => emit(root, "slhx:sse-error", url));
diff --git a/slhx-js/tests/runtime.rs b/slhx-js/tests/runtime.rs
index d7388cb..fa8aab8 100644
--- a/slhx-js/tests/runtime.rs
+++ b/slhx-js/tests/runtime.rs
@@ -218,12 +218,15 @@ fn runtime_refuses_partial_updates_on_fingerprint_mismatch() {
 
 #[test]
 fn runtime_applies_sse_effect_batches_inside_roots() {
-    // req: push/001 req: push/003 req: runtime/001
+    // req: push/001 req: push/003 req: push/006 req: runtime/001
     let source = slhx_js::RUNTIME_JS;
 
     assert!(source.contains("const sseSources = new WeakMap()"));
     assert!(source.contains("const url = root.getAttribute(\"data-slhx-sse\")"));
-    assert!(source.contains("new EventSource(new URL(url, location.href).href)"));
+    assert!(source.contains("const href = new URL(url, location.href)"));
+    assert!(source.contains("if (href.origin !== location.origin)"));
+    assert!(source.contains("emit(root, \"slhx:sse-error\", url)"));
+    assert!(source.contains("new EventSource(href.href)"));
     assert!(source.contains("source.addEventListener(\"slhx\", (event) => applySseMessage(root, event))"));
     assert!(source.contains("source.addEventListener(\"message\", (event) => applySseMessage(root, event))"));
     assert!(source.contains("applyBatch(bytes.buffer.slice(bytes.byteOffset, bytes.byteOffset + bytes.byteLength), root)"));