fix: declare and ship toolbar icons, so neither browser renders a puzzle piece (closes #371)

Neither manifest declared any icons, so both browsers showed a generic puzzle-piece -- the first thing seen on every browser start, and how a user tells a real extension from a look-alike. Both manifests now declare 16/32/48/128, and the PNGs ship inside each browser archive rather than being left at dist/ root, which is the trap that made a naive zip incomplete before.

build.js reads which icons to copy from each manifest's own icons block, so the manifest is the single source of truth and a declared-but-absent size fails the build rather than shipping a dangling reference; the packager's reference-resolver covers them independently. Manifest values are constrained before being joined into a path. The artwork is original, generated from geometry rather than traced or fetched.

tests/manifest.test.js

@@ -47,6 +47,12 @@ const fs = require("fs");
 const path = require("path");
 
 const MANIFEST_DIR = path.join(__dirname, "..", "manifest");
+const ROOT = path.join(__dirname, "..");
+
+// The sizes both stores and both toolbars ask for.
+const EXPECTED_ICON_SIZES = ["16", "32", "48", "128"];
+
+const PNG_SIGNATURE = Buffer.from("89504e470d0a1a0a", "hex");
 
 const EXPECTED_DIRECTIVES = {
     "default-src": ["'self'"],
@@ -115,6 +121,51 @@ function assertPolicy(policy) {
     }
 }
 
+// The declared icons, in both manifests.
+//
+// Without an "icons" block a browser draws a generic puzzle piece in the
+// toolbar for this extension, which is both the first thing the user sees and
+// how a real extension is told apart from a look-alike. Declaring one is not
+// enough on its own: an entry naming a file that is not in the tree ships a
+// reference to nothing, so the referenced bytes are read here and required to
+// be a PNG of the size the entry claims. build.js copies these into each
+// browser directory, relative to it, and script/lib/package.js then refuses to
+// build an archive that does not contain everything the manifest names.
+function assertIcons(target) {
+    const icons = readManifest(target).icons;
+    expect(Object.keys(icons).sort()).toEqual(EXPECTED_ICON_SIZES.sort());
+    for (const size of EXPECTED_ICON_SIZES) {
+        const ref = icons[size];
+        expect([size, ref]).toEqual([size, `icons/icon${size}.png`]);
+
+        const bytes = fs.readFileSync(path.join(ROOT, ref));
+        expect(bytes.subarray(0, 8)).toEqual(PNG_SIGNATURE);
+        // IHDR width and height, at fixed offsets right after the signature
+        // and the chunk header.
+        expect([ref, bytes.readUInt32BE(16), bytes.readUInt32BE(20)]).toEqual([
+            ref,
+            Number(size),
+            Number(size),
+        ]);
+    }
+}
+
+describe("declared icons", () => {
+    test("chrome declares real icons at every size", () => {
+        assertIcons("chrome");
+    });
+
+    test("firefox declares real icons at every size", () => {
+        assertIcons("firefox");
+    });
+
+    test("both targets declare the same icons", () => {
+        expect(readManifest("firefox").icons).toEqual(
+            readManifest("chrome").icons,
+        );
+    });
+});
+
 describe("shipped Content Security Policy", () => {
     // MV3 takes an object and applies extension_pages to the popup and the
     // background service worker, which is where libsodium runs.