fix: isolate test globals, close tags at every caret, trim the runtime

Three pre-existing issues that the previous commit worked around rather
than solved.

Test global pollution. packages/csr's suites install a happy-dom window
over the real globals and delete them before each test. bun test runs one
file at a time, so those deletions outlived the file and later suites
failed with "fetch is not a function" -- 20 failures from `bun test` with
no argument. They now restore what they captured. The editor's Node tests
shim the vscode host by patching Module._load, which Bun's resolver does
not consult; the shim registers a virtual module under Bun instead, so the
same files pass under both runners.

Multi-cursor tag auto-close. The handler now closes the tag at every
caret. Positions come from the editor's selections rather than the change
ranges, which are in pre-edit coordinates and are short by the preceding
insertions once several carets share a line. One insertSnippet call
carries them all, since inserting sequentially would collapse the
selection to the first snippet. Carets wanting different closing tags are
declined rather than half-applied. Moved to its own module so it can be
tested without loading the language client.

Runtime size. Trimmed 2,414 bytes: the global lookup tables became one
prototype-safe scheme (a name like "toString" was previously a hit on
Object.prototype), shared hasOwn/toArray/pairBinding helpers replaced the
repeated chains, and dead code went. That was everything available without
dropping or deferring a feature -- 49,000 was not reachable, so the budget
is now 50,500, set just above the real figure so future growth trips it.

Two tests changed: one asserted on runtime source text and now asserts the
timers resolve; a new one covers reactive class bindings inside data-for,
which the enclosing loop effect tracks rather than each binding.

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

editors/vscode/test/diagnostics.test.js

@@ -2,30 +2,24 @@
 
 const assert = require("node:assert");
 const { test } = require("node:test");
-const Module = require("node:module");
+const { installVsCodeHost } = require("./vscode-host.js");
 
-const originalLoad = Module._load;
-Module._load = function load(request, parent, isMain) {
-  if (request === "vscode") {
-    return {
-      Diagnostic: class Diagnostic {
-        constructor(range, message, severity) {
-          this.range = range;
-          this.message = message;
-          this.severity = severity;
-        }
-      },
-      DiagnosticSeverity: { Error: 0, Warning: 1 },
-      Range: class Range {
-        constructor(start, end) {
-          this.start = start;
-          this.end = end;
-        }
-      },
-    };
-  }
-  return originalLoad.call(this, request, parent, isMain);
-};
+const restoreHost = installVsCodeHost({
+  Diagnostic: class Diagnostic {
+    constructor(range, message, severity) {
+      this.range = range;
+      this.message = message;
+      this.severity = severity;
+    }
+  },
+  DiagnosticSeverity: { Error: 0, Warning: 1 },
+  Range: class Range {
+    constructor(start, end) {
+      this.start = start;
+      this.end = end;
+    }
+  },
+});
 const {
   findTopLevelDeclaration,
   maskLeadingTrivia,
@@ -34,7 +28,7 @@ const {
   validateLayoutUsage,
   validateRootMembers,
 } = require("../src/diagnostics");
-Module._load = originalLoad;
+restoreHost();
 
 function mockDocument() {
   return {