From 11988d60a6e43c43ee21bbf082fada3f28e0ae86 Mon Sep 17 00:00:00 2001
From: Natalie <natalie@lilithuwu.com>
Date: Thu, 25 Jun 2026 06:26:01 -0400
Subject: [PATCH] =?UTF-8?q?test(@projects/@magic-civilization):=20?=
 =?UTF-8?q?=E2=9B=B5=20p3-18=20P6-core=20=E2=80=94=20end-to-end=20proof=20?=
 =?UTF-8?q?an=20army=20fords=20open=20ocean=20to=20a=20far=20landmass?=
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The scenario that motivated p3-18: an army on landmass A reaching landmass B
across an ocean strip. teched_army_fords_open_ocean_to_far_landmass asserts the
full chain through process_move_requests — without naval tech the ocean rejects
the move (army stays put); with ocean_navigation (Ocean embark) the army crosses
the strip onto the far landmass and auto-disembarks on arrival.

Deterministic, cargo-verifiable evidence (the project's preferred proof form), no
dylib/Godot needed. The full headless 1v1-to-game_over demo (P6-full) is the
heavier dylib follow-up.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 src/simulator/crates/mc-turn/src/processor.rs | 55 +++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/src/simulator/crates/mc-turn/src/processor.rs b/src/simulator/crates/mc-turn/src/processor.rs
index 27a44ee9..ab3a563d 100644
--- a/src/simulator/crates/mc-turn/src/processor.rs
+++ b/src/simulator/crates/mc-turn/src/processor.rs
@@ -5230,6 +5230,61 @@ mod move_request_tests {
         assert_eq!(state.players[0].unit_upkeep.len(), 1, "unit_upkeep stays index-aligned");
     }
 
+    /// p3-18 end-to-end — the motivating scenario: an army on landmass A reaches
+    /// landmass B across an open-ocean strip. Without naval tech the ocean blocks
+    /// it; with `ocean_navigation` (Ocean embark) it fords the water and lands.
+    #[test]
+    fn teched_army_fords_open_ocean_to_far_landmass() {
+        // Landmass A (cols 0–1) | ocean strip (col 2) | landmass B (cols 3–4).
+        let mut grid = GridState::new(5, 5);
+        for r in 0..5 {
+            for c in 0..5 {
+                let idx = grid.idx(c, r);
+                grid.tiles[idx].biome_label_id =
+                    if c == 2 { "ocean" } else { "plains" }.to_string();
+            }
+        }
+        let mut state = GameState::default();
+        state.grid = Some(grid);
+        state
+            .units_catalog
+            .load_json_str(r#"[{"id":"warrior","movement":10,"domain":"land"}]"#)
+            .expect("catalog loads");
+        state.players.push(PlayerState {
+            player_index: 0,
+            units: vec![MapUnit {
+                id: 1, col: 0, row: 0, unit_id: "warrior".into(), ..MapUnit::default()
+            }
+            .with_moves(10)],
+            ..PlayerState::default()
+        });
+
+        // No naval tech (embark None) → the ocean strip is impassable.
+        state.pending_move_requests.push(move_req(0, (4, 0)));
+        let out = process_move_requests(&mut state);
+        assert!(
+            matches!(out[0], MoveOutcome::Rejected { .. }),
+            "without embark the ocean blocks the army, got {:?}",
+            out[0]
+        );
+        assert_eq!((state.players[0].units[0].col, state.players[0].units[0].row), (0, 0));
+
+        // ocean_navigation grants Ocean embark → the army fords to landmass B.
+        state.players[0].embark_level = mc_core::EmbarkLevel::Ocean;
+        state.players[0].units[0].movement_remaining = 10;
+        state.pending_move_requests.push(move_req(0, (4, 0)));
+        process_move_requests(&mut state);
+        assert_eq!(
+            (state.players[0].units[0].col, state.players[0].units[0].row),
+            (4, 0),
+            "ocean-teched army crossed the strip onto the far landmass"
+        );
+        assert!(
+            !state.players[0].units[0].is_embarked,
+            "auto-disembarked on arrival at land"
+        );
+    }
+
     #[test]
     fn zero_budget_rejects() {
         let mut state = build_state_with_unit(7, (0, 0), 0, |_, _| "plains");