Add browser best match option

browser/extension/background.test.cjs

@@ -69,6 +69,7 @@ test("shouldContinueWatchingState keeps polling locked login pages", () => {
 
 test("default settings include a blank bearer token that can be overridden by harness patching", () => {
   assert.equal(background.defaultSettings.bearerToken, "");
+  assert.equal(background.defaultSettings.bestMatchOnly, false);
 });
 
 test("savePlanForObservedLogin prefers updating an exact username match", () => {
@@ -129,3 +130,22 @@ test("savePlanForObservedLogin falls back to saving into the current page group"
     url: "https://vault.example.invalid/login"
   });
 });
+
+test("applyBestMatchOnly keeps only the strongest quality band when enabled", () => {
+  const filtered = background.applyBestMatchOnly([
+    { id: "livingston", title: "Livingston Dell", quality: "exact" },
+    { id: "rusty", title: "Rusty Ryan", quality: "host" },
+    { id: "linus", title: "Linus Caldwell", quality: "scheme" }
+  ], true);
+
+  assert.deepEqual(filtered.map((match) => match.id), ["livingston"]);
+});
+
+test("applyBestMatchOnly preserves all matches when disabled", () => {
+  const filtered = background.applyBestMatchOnly([
+    { id: "livingston", title: "Livingston Dell", quality: "exact" },
+    { id: "rusty", title: "Rusty Ryan", quality: "host" }
+  ], false);
+
+  assert.deepEqual(filtered.map((match) => match.id), ["livingston", "rusty"]);
+});