test(loadbearing): close the vacuous-negative class across the whole suite

Oekt 17 found the class on four named files. This sweep ENUMERATES it: 42 negative
substring assertions across 21 test files (STATE's "~34 across 23" was a premise --
measured, it is 42/21). Sixteen of them measured an absence without ever having
shown presence; all sixteen now carry a positive control asserting the searched-for
string PRESENT in the source artifact, in EXACTLY the form the negative looks for.

Files touched: test_costsim, test_loop, test_okf (3 sites), test_preflight,
test_run_entrance, test_s10_run_layer, test_sdk_version_guard, test_simulation
(2 sites), test_step1_expel, test_step5_refine, test_step7_async_loop,
test_step8_promotion, test_valuereport.

VALUE-PROOF (green-without / red-with, per the oekt-17 rule that a detach proof is
not a value proof). Seven source/fixture mutations, each making the negative vacuous:

  M1 verdict fixture loses the realization signal        VALUE-PROVEN
  M2 decoy fixture loses its text                        VALUE-PROVEN
  M3 renderer stops emitting typed section headings      VALUE-PROVEN
  M4 promotion stops writing the marker                  VALUE-PROVEN (pass 2)
  M5 fold stops rendering the realization surface        VALUE-PROVEN
  M6 report stops labelling the cost section             VALUE-PROVEN
  M7 preflight stops importing the SDK                   VALUE-PROVEN

M4 needed pass 2: a PRECEDING assertion caught the same mutation, hiding the new
control behind it -- the oekt-17 lesson reproduced. The remaining nine controls are
vacuity guards (non-emptiness / form-presence) whose mutation would have to break
the source artificially; they are stated as guards, not claimed as value-proven.

MEASURED FINDING (test_loop): the FIRST-RUN-MARKER negative cannot be given a
positive control at all. Within a run only the CHECKER's critique is fed back --
the proposer's own prior reasoning crosses no prompt boundary, not even within a
run. So that negative holds trivially. Left in place with the limitation stated in
the test rather than dressed up as a controlled seam; the CRITIQUE negative beside
it IS controlled and is the real seam.

Mutations were in-place on src/ and shared/ with original bytes restored and
sha-verified; git status clean before and after. Suite 688 -> 688 (assertions added
inside existing tests, no new test cases). ruff + mypy --strict green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Vc5PmZGjwuJypdhzKnJa5

tests/test_loop.py

@@ -162,6 +162,19 @@ class TestRunDebate:
         )
         run_debate(client, "context A", max_rounds=2, meter=_meter())
         run_debate(client, "context B", max_rounds=2, meter=_meter())
+        # Positive control for the CRITIQUE negative: within the first run the critique
+        # DOES reach the proposer's second prompt, in EXACTLY the form the negative
+        # below searches for. That is what makes "absent from run B" a measured seam
+        # rather than a string that never travels anywhere.
+        first_run_second_prompt = client.prompts("proposer")[1]
+        assert "FIRST-RUN-CRITIQUE" in first_run_second_prompt
+        # MEASURED (this session): no such control exists for FIRST-RUN-MARKER — the
+        # proposer's own prior reasoning crosses NO prompt boundary, not even within a
+        # run (only the checker's critique is fed back). So the marker negative below is
+        # a weaker, complementary check: it cannot go red by state leaking through the
+        # transcript, because that channel carries the critique alone. Stated, not
+        # dressed up as a controlled seam.
+        assert "FIRST-RUN-MARKER" not in first_run_second_prompt
         second_run_opening = client.prompts("proposer")[2]
         assert "FIRST-RUN-MARKER" not in second_run_opening
         assert "FIRST-RUN-CRITIQUE" not in second_run_opening