Adds a unit test to components_unittests (Android-only target) that
demonstrates the desync deterministically: while CredMan is showing for the
victim form F1, an AskForValuesToFill for an unrelated attacker-origin form F2
overwrites session_state_->current_field.origin without touching
session_state_->form, so a subsequent OnAutofillAvailable would fill F1 with
triggered_origin = attacker.test.

Build & run on an Android checkout:
  autoninja -C out/Android components_unittests
  out/Android/bin/run_components_unittests \
    --gtest_filter=AndroidAutofillProviderWithCredManTest.CredManEarlyReturnDesyncsOriginFromSessionForm

--- a/components/android_autofill/browser/android_autofill_provider_unittest.cc
+++ b/components/android_autofill/browser/android_autofill_provider_unittest.cc
@@ -1059,6 +1059,57 @@ TEST_F(AndroidAutofillProviderWithCredManTest, NotifyFocusOnCredManError) {
   completed_callback.Run(/*success=*/false);
 }

+// Regression POC: while the CredMan bottom sheet is showing for the linked
+// form F1, an AskForValuesToFill for an unrelated form F2 (different origin)
+// hits the early-return at OnAskForValuesToFill() AFTER UpdateCurrentField()
+// has overwritten current_field.origin. session_state_->form is still F1, so
+// OnAutofillAvailable() will call FillOrPreviewForm(F1, ..., F2.origin) and
+// IsSafeToFill evaluates with the attacker-chosen triggered_origin.
+TEST_F(AndroidAutofillProviderWithCredManTest,
+       CredManEarlyReturnDesyncsOriginFromSessionForm) {
+  base::RepeatingCallback<void(bool)> completed_callback;
+  EXPECT_CALL(cred_man_delegate(), SetRequestCompletionCallback)
+      .WillOnce(SaveArg<0>(&completed_callback));
+
+  // Step 2+3: user taps the webauthn field in F1 -> StartNewSession(F1) and
+  // ShowCredManSheet -> credman_sheet_status_ = kIsShowing.
+  FocusFormField(webauthn_email_field());
+  ASSERT_TRUE(test_api(autofill_provider()).form());
+  EXPECT_EQ(test_api(autofill_provider()).form()->form().global_id(),
+            test_form().global_id());
+  const url::Origin victim_origin =
+      test_api(autofill_provider()).last_focused_field_origin();
+
+  // Step 4: compromised renderer in another origin sends AskForValuesToFill
+  // for an unrelated form F2 while CredMan is showing.
+  const url::Origin attacker_origin =
+      url::Origin::Create(GURL("https://attacker.test"));
+  FormData f2 = CreateFormDataForFrame(CreateTestPersonalInformationFormData(),
+                                       main_frame_token());
+  test_api(f2).field(0).set_origin(attacker_origin);
+  android_autofill_manager().OnFormsSeen({f2}, /*removed_forms=*/{});
+  // No new framework session must start (early-return path).
+  EXPECT_CALL(provider_bridge(), StartAutofillSession).Times(0);
+  android_autofill_manager().SimulateOnAskForValuesToFill(f2, f2.fields()[0]);
+  Mock::VerifyAndClearExpectations(&provider_bridge());
+
+  // BUG: current_field.origin was overwritten with the attacker origin...
+  EXPECT_EQ(test_api(autofill_provider()).last_focused_field_origin(),
+            attacker_origin);
+  // ...but session_state_->form is still the victim's F1.
+  ASSERT_TRUE(test_api(autofill_provider()).form());
+  EXPECT_EQ(test_api(autofill_provider()).form()->form().global_id(),
+            test_form().global_id());
+  EXPECT_NE(test_api(autofill_provider()).last_focused_field_origin(),
+            victim_origin);
+
+  // Step 5: OnCredManUiClosed does not repair current_field.
+  completed_callback.Run(/*success=*/true);
+  EXPECT_EQ(test_api(autofill_provider()).last_focused_field_origin(),
+            attacker_origin);
+  // OnAutofillAvailable() would now call FillOrPreviewForm(R_mgr, F1, ...,
+  // triggered_origin = attacker_origin).
+}
+
 class AndroidAutofillProviderPrefillRequestTest
     : public AndroidAutofillProviderTestBase,