test(flows): actually pin the per-encounter no-op

The test demonstrated the fallback and guarded the dead shapes in two
halves that never met: the demonstrating half drives _handle_form_step,
which never calls validate_step_values -- only the walkers do. So nothing
put the fallback shape through the validator, and tightening `any` to
`all` killed the capability with the whole file still green. Measured: 73
passed under that mutation.

One line puts the same shape through the validator. Now 73 passed
unmutated, 1 failed under the mutation, failing on the fallback assertion
rather than incidentally on a dead shape another test already covers.

Found by Patch76 review on #2256.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012d29UJTiH4Uy2Pm37SBPtr

Author: kingpanther13

tests/src/unit/test_flow_options_preserve.py

@@ -1163,6 +1163,11 @@ def test_an_empty_object_in_a_list_is_a_per_encounter_no_op(self) -> None:
 
         # Encounter one falls back to what it would have been; two is addressed.
         assert seen == ["BW", "NY"]
+        # Put the SAME shape through the validator. Without this the two halves
+        # test different code — _handle_form_step never calls the validator,
+        # only the walkers do — so tightening `any` to `all` would kill the
+        # capability with the suite still green (Patch76 review, #2256).
+        validate_step_values({"step_values": {"init": [{}, {"province": "NY"}]}})
         # ...while an entry that applies nothing anywhere is still rejected.
         for dead in ([{}], [], {}, [{}, {}]):
             with pytest.raises(ToolError):