harden: stop the background reading the shared state singleton, and enforce it at build time (closes #324)

Five defects, one of which destroyed every wallet, came from src/background reading and writing the module-level state singleton the MV3 worker never populates, which silently served DEFAULT_STATE. Each point fix created the next defect. The background now has its own per-call getState() and a queued read-modify-write updateState(); the singleton is unreachable from it, and an unpopulated read throws instead of serving defaults.

The prohibition is enforced by the build, not by review: build.js asserts over esbuild's own metafile that no forbidden module is an input of a background bundle, so every specifier syntax esbuild resolves is covered, and both halves of the table are checked for rot -- a stale key, a stale module, an empty list, or an unlisted entry point under src/background/ all fail the build. The ESLint rule remains as fast local feedback and reads the same shared table. Known bounds are documented where the table lives.

Also closes #320: getProvider() now requires a validated network id, so a cold worker no longer prepares a non-mainnet dApp transaction for mainnet and gets refused by the wallet's own verifier. backgroundRefresh() no longer mutates address objects across a network round trip, the broadcast path takes its endpoint and chain id from one snapshot, and eight test storage stubs now structured-clone on get as the real chrome.storage.local does.

closes #320

tests/settingsUtcTimestamps.test.js

@@ -9,6 +9,8 @@
 const fs = require("fs");
 const path = require("path");
 
+const { makeStorageStub } = require("./support/storageStub");
+
 const POPUP_HTML = fs.readFileSync(
     path.join(__dirname, "..", "src", "popup", "index.html"),
     "utf8",
@@ -51,19 +53,17 @@ describe("the UTC Timestamps checkbox placement", () => {
 });
 
 describe("the UTC Timestamps setting round-trips through storage", () => {
-    let store;
+    let storage;
 
+    // The stub clones in both directions, as the real chrome.storage.local
+    // does. It used to alias, which is fatal to a round-trip test in
+    // particular: the object the module holds and the object "storage" holds
+    // are then the same object, so the setting appears to have been persisted
+    // and read back on a build where neither happened. See
+    // tests/support/storageStub.js.
     function loadStateModule() {
-        store = {};
-        global.chrome = {
-            storage: {
-                local: {
-                    get: async (key) =>
-                        key in store ? { [key]: store[key] } : {},
-                    set: async (obj) => Object.assign(store, obj),
-                },
-            },
-        };
+        storage = makeStorageStub();
+        global.chrome = { storage };
         jest.resetModules();
         return require("../src/shared/state");
     }
@@ -86,12 +86,18 @@ describe("the UTC Timestamps setting round-trips through storage", () => {
         // What the change handler in views/settings.js does.
         first.state.utcTimestamps = true;
         await first.saveState();
-        expect(store.autistmask.utcTimestamps).toBe(true);
+        expect(storage.read("autistmask").utcTimestamps).toBe(true);
 
-        // A fresh popup load sees it.
+        // A fresh popup load sees it — and, before that load, refuses to
+        // answer at all rather than reporting the default. That refusal is
+        // what makes the assertion below evidence of a read from storage
+        // instead of a value that was already sitting in memory
+        // (https://git.eeqj.de/sneak/AutistMask/issues/324).
         jest.resetModules();
         const second = require("../src/shared/state");
-        expect(second.state.utcTimestamps).toBe(false);
+        expect(() => second.state.utcTimestamps).toThrow(
+            second.StateNotLoadedError,
+        );
         await second.loadState();
         expect(second.state.utcTimestamps).toBe(true);
     });