fix(conformance): g4 reads a doubling out of what the field grew by

The whole-value check misses a driver that typed the value twice onto content
the field already held, which is the append-vs-replace shape the recorded value
used to catch before it was redacted. What the field grew by over the snapshot
the action was chosen against is the same signal and needs no typed value.

Checked against every recorded trace under conformance/runs: 485 traces, 299 of
them carrying an InputText, none newly failing.

conformance/gates.sh

@@ -164,9 +164,10 @@ gate_clear_state() {
 # placeholder (internal/verifier/redaction.go), and android reports that fact
 # for nothing, so on that backend every InputText records the placeholder. The
 # OBSERVED value is never redacted, and a field holding one string twice over is
-# the doubling itself. A value that is a single character repeated is exempt:
-# the input corpus types "a" 4096 times and a pair of spaces, and neither can be
-# told apart from its own doubling.
+# the doubling itself, whether that is the whole value or what the value grew by
+# over the snapshot the action was chosen against. A value that is a single
+# character repeated is exempt: the input corpus types "a" 4096 times and a pair
+# of spaces, and neither can be told apart from its own doubling.
 gate_no_doubled_text() {
   local run_directory="$1"
   local trace_file="${run_directory}/trace.jsonl"
@@ -200,10 +201,16 @@ gate_no_doubled_text() {
             | ($current.next_action.text // "") as $typed
             | (($next.hierarchy.elements // [])
                | map(select(.resourceId == $field)) | first) as $element
+            | (($current.hierarchy.elements // [])
+               | map(select(.resourceId == $field)) | first) as $before
             | if $element != null
               then
                 (($element.attrs.text // $element.text // "")) as $value
+                | (($before.attrs.text // $before.text // "")) as $previous
+                | (if $previous != "" and ($value | startswith($previous))
+                   then $value[($previous | length):] else "" end) as $appended
                 | if self_doubled($value)
+                     or self_doubled($appended)
                      or ($typed != "" and $typed != $redacted
                          and ($value | contains($typed + $typed)))
                   then . + [{field: $field, value: $value}]