combat-pincer-coordination: per-tier maps reinforce two-prong doctrine

Replaces the generic rush-hour-arena with three custom-built 128x48
arenas that physically reinforce what this pack measures (synchronous
NW + SW two-prong arrival on a central cluster). The actor layouts,
predicates, and survival/kill bars are unchanged; the new maps add
WATER walls that close the band between each spawn and the engagement
axis, so neither squad can shortcut onto the other's lane and
"merge" into a single approach (which would weaken the two-prong
discrimination).

Map design (mapgen 'arena' generator + obstacle clusters):

All tiers — 128x48 cordon 2; walls y=12..16 and y=24..28 across
x=10..40 carve a NORTH lane (y=2..11) and a SOUTH lane (y=29..45)
that the NW spawn (5,8) and SW spawn (5,32) must take respectively.
The central engagement axis y=17..23 stays open at x>=41 so both
prongs converge ON the cluster from off-axis directions.

* easy - combat-pincer-coordination-easy (light infantry cluster)
* medium - combat-pincer-coordination-medium (+ enemy 2tnk armour)
* hard - combat-pincer-coordination-hard (medium cluster + the
existing spawn-point round-robin: group 0 at (5,8)/(5,32),
group 1 at (3,5)/(3,35); all staging cells sit in the
open NORTH or SOUTH bands so the wall layout works for
both seed groups).

Smoke check: every level compiles with map_supported=True; all
actors in-bounds (x in [0..127], y in [0..47]); no actor placed
on a WATER cell.

openra_bench/scenarios/packs/combat-pincer-coordination.yaml

@@ -16,6 +16,21 @@
 # defender cannot focus on either prong in detail.
 #
 # Engine notes (per CLAUDE.md):
+#   - Map: per-tier custom 128x48 arena (cordon 2 ⇒ playable y in
+#     [2..45]) generated via mapgen's `arena` generator with WATER
+#     walls that physically reinforce the two-prong pincer doctrine:
+#       * easy / medium: walls y=12..16 and y=24..28 across x=10..40
+#         carve a TWO-PRONG approach. NW spawn (5,8) routes east via
+#         the open band y=2..11 (reaching the cluster from the north
+#         flank); SW spawn (5,32) routes east via the open band
+#         y=29..45. The central engagement axis y=17..23 is open at
+#         x>=41 so both prongs converge ON the cluster from off-axis
+#         directions — no shortcut to "merge" the squads onto a
+#         single approach lane.
+#       * hard: same 128x48 wall layout plus the existing two-spawn-
+#         group axis (group 0 stages at (5,8)/(5,32), group 1 at
+#         (3,5)/(3,35)) so the exact start cells differ across seeds
+#         and a memorised single-cell opening cannot generalise.
 #   - Enemy cluster anchored at (50,19) / (50,21) — CLAUDE.md warns
 #     that (50,20) silently fails to place enemy clusters; the off-by-
 #     one cells are confirmed working. The win region centre at
@@ -165,6 +180,26 @@ levels:
       can't satisfy the four-in-region clause. Six kills, four tanks at
       (50,20), no more than two losses, within about 50 turns.
     overrides:
+      # EASY MAP — 128x48 arena (cordon 2 -> playable y in [2..45]).
+      # Two-prong corridors: walls y=12..16 and y=24..28 across
+      # x=10..40 carve a NORTH lane (y=2..11) and a SOUTH lane
+      # (y=29..45) that NW and SW spawns must take respectively.
+      # The central engagement axis y=17..23 is open at x>=41 so
+      # both prongs converge ON the cluster at (50,20) from off-axis
+      # directions; no shortcut allows one squad to absorb the
+      # other's role.
+      base_map:
+        generator: arena
+        name: combat-pincer-coordination-easy
+        width: 128
+        height: 48
+        cordon: 2
+        title: 'Pincer Coordination — Easy (Two-Prong Approach)'
+        obstacles:
+          # NORTH wall — closes y=12..16 across x=10..40.
+          - {x: 10, y: 12, w: 31, h: 5}
+          # SOUTH wall — closes y=24..28 across x=10..40.
+          - {x: 10, y: 24, w: 31, h: 5}
       actors:
         # Squad A (NORTH-WEST) — 3 medium tanks at (5,8).
         - {type: 2tnk, owner: agent, position: [5, 8],  stance: 1, count: 3}
@@ -232,6 +267,21 @@ levels:
       kills, four tanks in the (50,20) disc, no more than two losses,
       within about 50 turns.
     overrides:
+      # MEDIUM MAP — 128x48 arena (cordon 2 -> playable y in [2..45]).
+      # Same two-prong wall layout as easy: walls y=12..16 and
+      # y=24..28 across x=10..40 force the NW and SW squads onto
+      # off-axis lanes that converge on the cluster from above and
+      # below.
+      base_map:
+        generator: arena
+        name: combat-pincer-coordination-medium
+        width: 128
+        height: 48
+        cordon: 2
+        title: 'Pincer Coordination — Medium (Armoured Cluster)'
+        obstacles:
+          - {x: 10, y: 12, w: 31, h: 5}
+          - {x: 10, y: 24, w: 31, h: 5}
       actors:
         - {type: 2tnk, owner: agent, position: [5, 8],  stance: 1, count: 3}
         - {type: 2tnk, owner: agent, position: [5, 32], stance: 1, count: 3}
@@ -297,6 +347,23 @@ levels:
       bleeds out. Six kills, four tanks in the (50,20) disc, two losses or
       fewer, within about 50 turns.
     overrides:
+      # HARD MAP — 128x48 arena (cordon 2 -> playable y in [2..45]).
+      # Same two-prong wall layout as easy/medium plus the existing
+      # spawn-point round-robin: spawn_point 0 stages at (5,8)/(5,32),
+      # spawn_point 1 at (3,5)/(3,35). All staging cells sit in the
+      # open NORTH band (y=2..11) or SOUTH band (y=29..45); the wall
+      # bands y=12..16 and y=24..28 across x=10..40 still force the
+      # two-prong off-axis approach regardless of seed.
+      base_map:
+        generator: arena
+        name: combat-pincer-coordination-hard
+        width: 128
+        height: 48
+        cordon: 2
+        title: 'Pincer Coordination — Hard (Spawn-Varied Two-Prong)'
+        obstacles:
+          - {x: 10, y: 12, w: 31, h: 5}
+          - {x: 10, y: 24, w: 31, h: 5}
       actors:
         # spawn_point 0 — Squad A NORTH (5,8), Squad B SOUTH (5,32).
         - {type: 2tnk, owner: agent, position: [5, 8],  stance: 1, count: 3, spawn_point: 0}