Add test for SSE connection pool leak

server/tests/sse_cleanup_test.rs

@@ -0,0 +1,47 @@
+//! Regression: SSE connection-pool leak via missing `EventSource.close()`.
+//!
+//! Every HTML template that opens `new EventSource('/web/events')` must
+//! also close it on `pagehide`. Without the close, Chrome keeps the
+//! socket in a "draining" state after navigation; after ~6 rapid
+//! back-and-forth navigations all 6 per-origin pool slots are draining
+//! and new requests stall with `blocked` timings of 15-30 seconds
+//! (confirmed by HAR capture on 2026-04-20).
+
+use std::fs;
+use std::path::Path;
+
+#[test]
+fn every_event_source_template_closes_it_on_pagehide() {
+    let template_dir = Path::new(env!("CARGO_MANIFEST_DIR")).join("templates");
+    let entries = fs::read_dir(&template_dir).expect("templates directory readable");
+
+    let mut checked = 0;
+    let mut missing: Vec<String> = Vec::new();
+
+    for entry in entries {
+        let path = entry.unwrap().path();
+        if path.extension().and_then(|s| s.to_str()) != Some("html") {
+            continue;
+        }
+        let content = fs::read_to_string(&path).unwrap();
+        if !content.contains("new EventSource('/web/events')") {
+            continue;
+        }
+        checked += 1;
+        let has_pagehide = content.contains("pagehide");
+        let has_close = content.contains(".close()");
+        if !(has_pagehide && has_close) {
+            missing.push(path.file_name().unwrap().to_string_lossy().into_owned());
+        }
+    }
+
+    assert!(
+        checked >= 1,
+        "test itself is stale: no template contains EventSource('/web/events')",
+    );
+    assert!(
+        missing.is_empty(),
+        "templates open EventSource but lack `pagehide` + `.close()` cleanup: {missing:?} \
+         — this leaks Chrome socket-pool slots and stalls navigation after ~6 cycles",
+    );
+}