fix(realtime): force-destroy pg socket on cleanup timeout (SSE leak) (#44)

Three SSE-routes (solo, backlog, notifications) each create a long-
running pg.Client that LISTENs on scrum4me_changes. On abrupt close
(Fast Refresh, browser refresh, Vercel function recycle) the
pgClient.end()-await sometimes hangs silently, leaving the underlying
socket connected to Postgres. The connection stays in 'idle' on Neon's
side and after ~10-20 reconnects the connection-pool fills up — new
SSE connects fail with ERR_INCOMPLETE_CHUNKED_ENCODING in the browser.

Fix: shared `closePgClientSafely` helper that races client.end()
against a 2 s timeout; on timeout it force-destroys the underlying
socket so the OS releases the FD and Postgres notices the disconnect.

Validated by direct DB inspection: 18 stale 'idle LISTEN'-connections
were piled up before the fix; after manual pg_terminate_backend cleanup
the SSE-stream stabilised. This change makes the pile-up impossible
going forward.

- new lib/realtime/pg-client-cleanup.ts
- 3 routes use the helper instead of bare `await pgClient.end()`
- 3 unit tests for the helper (timely-end, hang-falls-back-to-destroy,
  end-rejection-is-swallowed)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/realtime/pg-client-cleanup.ts

@@ -0,0 +1,55 @@
+// Robust pg.Client cleanup for SSE-routes that hold a long-running LISTEN-
+// connection. Without this helper, `pgClient.end()` can hang silently when
+// the underlying socket is in a weird state (Fast Refresh, abrupt browser
+// close, Vercel function recycle), leaving the connection in 'idle' on the
+// Postgres server. After ~10-20 reconnects the Neon connection-pool fills
+// up and new SSE-connections fail with ERR_INCOMPLETE_CHUNKED_ENCODING.
+//
+// Strategy: race `pgClient.end()` against a short timeout; if the timeout
+// wins, force-destroy the underlying socket so the OS releases the FD and
+// Neon notices the disconnect.
+
+import type { Client } from 'pg'
+
+const END_TIMEOUT_MS = 2_000
+
+interface PgClientWithStream {
+  connection?: { stream?: { destroy?: (err?: Error) => void } }
+}
+
+export async function closePgClientSafely(
+  client: Client,
+  label: string,
+): Promise<void> {
+  // Drop notification/error handlers so a late event from the dying
+  // connection cannot trigger downstream cleanup again.
+  client.removeAllListeners('notification')
+  client.removeAllListeners('error')
+  client.on('error', () => {
+    // Swallow: connection is being torn down on purpose.
+  })
+
+  let timer: ReturnType<typeof setTimeout> | null = null
+  const timeout = new Promise<'timeout'>((resolve) => {
+    timer = setTimeout(() => resolve('timeout'), END_TIMEOUT_MS)
+  })
+
+  const result = await Promise.race([
+    client.end().then(() => 'ended' as const),
+    timeout,
+  ]).catch(() => 'error' as const)
+
+  if (timer) clearTimeout(timer)
+
+  if (result !== 'ended') {
+    if (process.env.NODE_ENV !== 'production') {
+      console.warn(`[${label}] pgClient.end() did not finish in ${END_TIMEOUT_MS}ms — forcing socket destroy`)
+    }
+    const stream = (client as unknown as PgClientWithStream).connection?.stream
+    try {
+      stream?.destroy?.(new Error(`forced socket destroy from ${label}`))
+    } catch {
+      // best-effort
+    }
+  }
+}