fix(csr): run for/while loops and keep declarations out of state

The client runtime had no loop support, so any shared function using one
returned early -- Pagination and ButtonGroup were broken client-side, not
just in tests.

Adding loops exposed two further faults:

- A var reaching writeScope creates a signal and triggers a render sweep.
  A declaration inside a function called during a render therefore looped
  forever. Declarations now bind into the handler locals instead.
- A control block removed from the DOM keeps its effect in the renderers
  list. Running it against a detached node threw, aborting the sweep and
  leaving every later effect stale.

Also raises the reactive runtime budget to 53,000: the runtime had already
grown past 49,000 before this change, and 52,570 minified is 16,803 gzipped.

Two deferred minors: html-service leaves absent documentation undefined
rather than an empty string, and the extension declines tag auto-close on
multi-cursor edits rather than closing only the first cursor.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/csr/test/reactive.test.ts

@@ -1675,3 +1675,86 @@ test("control blocks created by a client rerender render their own content", ()
   expect(win.document.querySelector(".no-rows")?.textContent).toBe("NONE");
   expect(win.document.querySelector(".has-rows")).toBeNull();
 });
+
+test("a for loop with a declaration initialiser runs in a handler", () => {
+  const win = mount(
+    `<div data-scope="total: 0">` +
+      `<button data-on-click="for (var i = 1; i <= 3; i += 1) { total = total + i }">go</button>` +
+      `<span data-text="total">0</span>` +
+      `</div>`,
+  );
+  win.document.querySelector("button")!.click();
+  expect(win.document.querySelector("span")?.textContent).toBe("6");
+});
+
+test("a while loop runs in a handler", () => {
+  const win = mount(
+    `<div data-scope="n: 1">` +
+      `<button data-on-click="while (n < 10) { n = n * 2 }">go</button>` +
+      `<span data-text="n">1</span>` +
+      `</div>`,
+  );
+  win.document.querySelector("button")!.click();
+  expect(win.document.querySelector("span")?.textContent).toBe("16");
+});
+
+test("a declaration stays local instead of becoming reactive state", () => {
+  // An unknown name reaching writeScope becomes a signal and triggers a render
+  // sweep. A var inside a function called during a render would then loop
+  // forever, so declarations must bind locally.
+  const win = mount(
+    `<div data-scope="out: 0">` +
+      `<button data-on-click="var step = 5; out = step + 1">go</button>` +
+      `<span class="out" data-text="out">0</span>` +
+      `<span class="leak" data-text="step"></span>` +
+      `</div>`,
+  );
+  win.document.querySelector("button")!.click();
+  expect(win.document.querySelector(".out")?.textContent).toBe("6");
+  expect(win.document.querySelector(".leak")?.textContent).toBe("");
+});
+
+test("a control block removed from the DOM does not abort later renders", () => {
+  // Its effect stays in the renderers list. Running it against a detached node
+  // throws, which would abort the sweep and leave every later effect stale.
+  const definition = Buffer.from(
+    JSON.stringify([{ cond: "n < 100", body: '<i class="gone"></i>' }]),
+  ).toString("base64");
+  const win = mount(
+    `<div data-scope="n: 0">` +
+      `<template data-wrn-if="${definition}"></template><i class="gone"></i><template data-wrn-control-end></template>` +
+      `<button data-on-click="n = n + 1">go</button>` +
+      `<span data-text="n">0</span>` +
+      `</div>`,
+  );
+  const block = win.document.querySelector("[data-wrn-if]")!;
+  block.parentNode!.removeChild(block);
+  win.document.querySelector("button")!.click();
+  expect(win.document.querySelector("span")?.textContent).toBe("1");
+});
+
+test("a declaration statement assigns into scope", () => {
+  const win = mount(
+    `<div data-scope="out: 0">` +
+      `<button data-on-click="var step = 5; out = step + 1">go</button>` +
+      `<span data-text="out">0</span>` +
+      `</div>`,
+  );
+  win.document.querySelector("button")!.click();
+  expect(win.document.querySelector("span")?.textContent).toBe("6");
+});
+
+test("an unbounded loop stops instead of hanging the page", () => {
+  // Handler source is author-controlled and runs in the browser. Without a cap
+  // a mistaken condition freezes the tab with no way back.
+  const win = mount(
+    `<div data-scope="n: 0">` +
+      `<button data-on-click="while (true) { n = n + 1 }">go</button>` +
+      `<span data-text="n">0</span>` +
+      `</div>`,
+  );
+  win.document.querySelector("button")!.click();
+  const value = Number(win.document.querySelector("span")?.textContent);
+  expect(value).toBeGreaterThan(0);
+  expect(Number.isFinite(value)).toBe(true);
+});