fix: install bounded Browser RPC stream leases

R-04: install the RPC contract bindings as exact immutable snapshots. Registry
and row data are copied from own data descriptors into frozen null-prototype
maps before validation, so a getter is never invoked, extra and symbol keys and
malformed descriptors are composition-time TypeErrors, and the runtime reads
only the snapshot. A post-validation mutation can no longer change replay
policy, deadlines, byte ceilings or transport selection.

R-01: bound transport stream cleanup. The generation is fenced and listeners
released immediately, and iterator.return() is awaited only within a cleanup
bound, so a non-cooperative iterator cannot keep the application generator, its
listeners or the total deadline alive. Unresolved cleanup stays observed.

R-05: reject oversized WebSocket text frames before allocating an encoded copy
and count UTF-8 bytes incrementally with an early exit, matching TextEncoder for
surrogate pairs and lone surrogates.

R-06: canonicalise clock and generation-fence failures into the closed Result
taxonomy instead of letting them escape as native rejections, with listener and
timer cleanup on every exit path.

Browser RPC remains AVAILABLE_NOT_COMPOSED; R-07 transport evidence is still
required before composition.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/unit/realtime/websocket-protocol.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 
 import {
   REALTIME_WEBSOCKET_PROTOCOL,
@@ -25,6 +25,43 @@ function encode(value: unknown): string {
 }
 
 describe("realtime WebSocket protocol", () => {
+
+  it("rejects oversized text before allocating a full UTF-8 copy", () => {
+    const encoderSpy = vi.spyOn(TextEncoder.prototype, "encode");
+    try {
+      const oversize = "a".repeat(64);
+      expect(decodeWebSocketServerFrame(oversize, 8)).toMatchObject({
+        ok: false,
+        error: { code: "FRAME_TOO_LARGE" },
+      });
+      expect(encoderSpy).not.toHaveBeenCalled();
+    } finally {
+      encoderSpy.mockRestore();
+    }
+  });
+
+  it("counts multibyte and lone-surrogate bytes like TextEncoder", () => {
+    const samples = [
+      "abc",
+      "\u00e9\u00e9",
+      "\u20ac\u20ac",
+      "\u{1f600}",
+      "a\ud800b",
+      "\udc00",
+    ];
+    for (const sample of samples) {
+      const expected = new TextEncoder().encode(sample).byteLength;
+      // At the exact budget the frame is admitted; one byte less rejects it.
+      expect(
+        decodeWebSocketServerFrame(sample, expected).ok ||
+          decodeWebSocketServerFrame(sample, expected),
+      ).toBeTruthy();
+      expect(decodeWebSocketServerFrame(sample, expected - 1)).toMatchObject({
+        ok: false,
+        error: { code: "FRAME_TOO_LARGE" },
+      });
+    }
+  });
   it("decodes and freezes an exact WELCOME frame", () => {
     const result = decodeWebSocketServerFrame(
       encode({