test(conformance): g4 sees a doubling appended to what the field held

Redaction cost the gate this shape on android: the driver typed the value twice
onto existing content, so the whole value is not its own doubling and the typed
value is not in the trace to compare against. The recorded-value check still
catches it on the backends that record one.

Red at this commit: G4 reports PASS on a field that grew by one string twice.

conformance/testdata/generate.py

@@ -152,6 +152,16 @@ write_run(
     ],
 )
 
+# G4: the driver typed the value twice onto what the field already held, so the
+# whole value is not its own doubling. What it grew by is.
+write_run(
+    "g4-appended-doubling",
+    [
+        step(1, 600, login_screen("demo@", ""), input_action("LoginEmail")),
+        step(2, 600, login_screen("[email protected]", "")),
+    ],
+)
+
 # G4: an action typed at coordinates names no field. The step carries nothing
 # the gate can check, and it may not stop the gate checking the rest.
 write_run(