security: announce a fresh EIP-6963 provider UUID per page load (closes #398)

The provider UUID was generated once, stored in extension storage, and
announced verbatim to every page on every load and across restarts, so any
site — connected or not — could read a stable cross-site, cross-session
identifier for the install: a supercookie contradicting the "no tracking"
promise. EIP-6963 wants a fresh UUIDv4 per announcement instead.

inpage.js now announces a per-load crypto.randomUUID() and persists nothing;
the eip6963Uuid storage key and the AUTISTMASK_PROVIDER_UUID content-script
message are removed. That key was a standalone top-level storage entry, never
part of the versioned autistmask profile, so stateSchema.js and the
persisted-field harness are untouched and no existing profile is affected.

A jest test asserts two loads announce different UUIDv4s and that one load
reuses a single UUID across re-announcements.

Model: opus-4-8

tests/inpageProviderUuid.test.js

@@ -0,0 +1,103 @@
+// The EIP-6963 provider UUID inpage.js announces (src/content/inpage.js).
+//
+// The bug this pins down (issue #398): the UUID used to be generated once,
+// persisted in extension storage, and announced verbatim to every page on
+// every load and across browser restarts, so any site — connected or not —
+// could read a stable cross-site, cross-session identifier for the install.
+// EIP-6963 wants a fresh UUIDv4 per announcement instead. The fix generates
+// it per page load and stores nothing.
+//
+// inpage.js is a bare IIFE injected into the page's JS context, not a module;
+// see tests/inpageErrors.test.js for why it is evaluated against a stub window
+// rather than imported. Here the stub captures the CustomEvent that carries
+// the announcement, so the UUID this file reads is the one a real dApp's
+// eip6963:announceProvider listener would see.
+
+const fs = require("fs");
+const path = require("path");
+const { webcrypto } = require("crypto");
+
+const SOURCE = fs.readFileSync(
+    path.join(__dirname, "..", "src", "content", "inpage.js"),
+    "utf8",
+);
+
+const loadInto = new Function(
+    "window",
+    "self",
+    "crypto",
+    "Event",
+    "CustomEvent",
+    SOURCE,
+);
+
+class StubEvent {
+    constructor(type) {
+        this.type = type;
+    }
+}
+
+class StubCustomEvent extends StubEvent {
+    constructor(type, init) {
+        super(type);
+        this.detail = init && init.detail;
+    }
+}
+
+// Evaluate inpage.js once against a fresh stub window and return every UUID it
+// announced. A `requestProvider` event is dispatched too, so a re-announcement
+// within one load is observed as well as the announcement at load.
+function announcedUuids() {
+    const listeners = {};
+    const uuids = [];
+
+    const win = {
+        addEventListener(type, fn) {
+            (listeners[type] || (listeners[type] = [])).push(fn);
+        },
+        removeEventListener(type, fn) {
+            const fns = listeners[type];
+            if (!fns) return;
+            const i = fns.indexOf(fn);
+            if (i !== -1) fns.splice(i, 1);
+        },
+        postMessage() {},
+        dispatchEvent(event) {
+            if (event.type === "eip6963:announceProvider") {
+                uuids.push(event.detail.info.uuid);
+            }
+            for (const fn of (listeners[event.type] || []).slice()) fn(event);
+            return true;
+        },
+    };
+    win.window = win;
+
+    loadInto(win, win, webcrypto, StubEvent, StubCustomEvent);
+    win.dispatchEvent(new StubEvent("eip6963:requestProvider"));
+    return uuids;
+}
+
+const UUID_V4 =
+    /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
+
+describe("the EIP-6963 provider UUID is fresh per page load", () => {
+    test("a load announces a UUIDv4, unprompted, with nothing delivered", () => {
+        const uuids = announcedUuids();
+        expect(uuids.length).toBeGreaterThan(0);
+        expect(uuids[0]).toMatch(UUID_V4);
+    });
+
+    test("every announcement within one load carries the same UUID", () => {
+        const uuids = announcedUuids();
+        expect(uuids.length).toBeGreaterThan(1);
+        expect(new Set(uuids).size).toBe(1);
+    });
+
+    test("two page loads announce different UUIDs", () => {
+        const first = announcedUuids()[0];
+        const second = announcedUuids()[0];
+        expect(first).toMatch(UUID_V4);
+        expect(second).toMatch(UUID_V4);
+        expect(second).not.toBe(first);
+    });
+});