feat(csr): add stripped dev output diagnostics

packages/csr/test/reactive.test.ts

@@ -1,6 +1,7 @@
 import { test, expect, beforeEach } from "bun:test";
 import { Window } from "happy-dom";
 import { REACTIVE_RUNTIME } from "../src/reactive-runtime.ts";
+import { getReactiveRuntime } from "../src/index.ts";
 import { mountHtml } from "@wrnexus/test";
 
 // Fresh DOM per test, with the runtime's globals bound.
@@ -663,6 +664,38 @@ test("a camelCase output reaches a parent binding despite attribute lowercasing"
   expect(win.document.querySelector("#out")?.textContent).toBe("yes");
 });
 
+test("development runtime warns once for an output with no parent binding", () => {
+  const win = new Window() as unknown as Window & Record<string, unknown>;
+  win.document.body.innerHTML =
+    `<div data-scope="" data-wrn-events="complete"><button data-on-click="output.complete({})">go</button></div>`;
+  (globalThis as Record<string, unknown>).window = win;
+  (globalThis as Record<string, unknown>).document = win.document;
+  (globalThis as Record<string, unknown>).location = win.location;
+  (globalThis as Record<string, unknown>).NodeFilter = (win as unknown as { NodeFilter: unknown }).NodeFilter;
+  (globalThis as Record<string, unknown>).MutationObserver = (win as unknown as { MutationObserver: unknown }).MutationObserver;
+  (globalThis as Record<string, unknown>).CustomEvent = (win as unknown as { CustomEvent: unknown }).CustomEvent;
+  const warnings: unknown[][] = [];
+  const originalWarn = console.warn;
+  console.warn = (...args: unknown[]) => warnings.push(args);
+  try {
+    (0, eval)(getReactiveRuntime(true));
+    (win as unknown as { __wrnexusHydrateScopes?: (root: unknown) => void }).__wrnexusHydrateScopes?.(win.document);
+    (win.document.querySelector("button") as unknown as HTMLElement).click();
+    (win.document.querySelector("button") as unknown as HTMLElement).click();
+  } finally {
+    console.warn = originalWarn;
+  }
+  expect(warnings).toHaveLength(1);
+  expect(String(warnings[0]?.[0])).toContain("WRN-DEV-OUTPUT-UNHANDLED");
+});
+
+test("production runtime strips development diagnostics", () => {
+  const production = getReactiveRuntime();
+  expect(production).not.toContain("WRN-DEV-");
+  expect(production).not.toContain("warnOnce");
+  expect(REACTIVE_RUNTIME).toContain("__WRNEXUS_DEV_START__");
+});
+
 // --- browser globals + regex literals in client expressions ----------------
 // Client functions and inline handlers are interpreted by the runtime's own
 // eval-free expression engine (so a strict CSP needs no unsafe-eval). Anything