H2's ATTACK dynamics, and a construction hazard found while measuring them

The H2 panel measured wins, variance and DARVO but not ATTACK selection —
which is F17's actual question. attack-value now runs H2 too.

The shape is the finding. Under H1 a seat that sometimes attacks loses
everything at 3p and above. Under H2 rank-75 wins 112/173/199 against
greedy's 120/175/199, while attacking and arming DARVO. So H2 makes
occasional ATTACK affordable — it does not make it pay. rank-75 never
beats greedy in any cell, and rank-95 (always attack) still wins 0
everywhere in all three variants, so "not always-attack-optimal" holds.

F17 therefore stands: ATTACK earns its place in no mode. What changed is
that choosing it is no longer catastrophic. Whether affordable is what the
design wants is ground-game's judgement.

And a hazard: with_variant() exists because H2 assigns Problem owners at
setup and `state.variant = v` leaves them unassigned, so scoped pressure
ticks nobody and H2 measures as INERT. Three call sites had the bare
write, including cb-play's driver.

No published figure is affected, and that was checked rather than assumed:
h2-panel used the builder, and the two harnesses with the bare write had
only ever run baseline and H1, neither of which has a setup step; the
driver has never played H2. All three fixed, and
a_bare_variant_write_leaves_h2_inert now states the difference so a
regression is caught by a named test rather than by a reader wondering why
H2 did nothing.

The builder was not enough — the field is public, so the old form still
compiles. Worth knowing before the next variant.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

games/ground/examples/attack-value.rs

@@ -120,7 +120,8 @@ fn sweep(
         st.mode = mode;
         // CB-WP-0038 T03: the SAME instrument measures both rule sets in
         // the same run. Two harnesses would compare harnesses.
-        st.variant = variant;
+        // `with_variant`, never a field write (see regulation.rs).
+        let st = st.with_variant(variant);
         let mut ps = mk(players);
         // CB-WP-0038 T03: a game the engine REFUSES is not a game the
         // table lost, and `else { continue }` made the two identical.
@@ -211,6 +212,10 @@ fn main() {
             "H1 h1-problem-stress",
             games_ground::Variant::H1ProblemStress,
         ),
+        (
+            "H2 h2-scoped-problem-stress",
+            games_ground::Variant::H2ScopedProblemStress,
+        ),
     ] {
         println!("================ {vlabel} ================\n");
         for (label, mode) in [