fix(@projects/@magic-civilization): 🛡️ p3-26 B2 — siege-suppress city healing (besieged cities don't heal)

Regression fix: the B2 healing phase ran end-of-turn BEFORE siege and healed cities
unconditionally — so a besieged city healed (e.g. 30→50 hp) before the same turn's siege
resolved, defeating captures (last_survivor_via_capture got empty events: a 30-hp city +
3 attackers @15 = 45 dmg no longer captured after healing to 50). Bisected to this session
(passed at e926345ad; the healing phase introduced the bug).

Fix: process_healing_phase now snapshots all units' tiles and SKIPS healing any city with an
enemy unit on its tile (under siege) — real-time siege-suppress matching the live game's intent
(its `last_attacked_turn` window). Un-besieged cities still heal. Tests:
besieged_city_does_not_heal (new) + last_survivor_via_capture (restored) + healing 11/0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/simulator/crates/mc-turn/src/healing.rs

@@ -65,7 +65,19 @@ const CITY_HEAL_PER_TURN: i32 = 20;
 /// This function does **not** call `step()` or any other phase — the parent
 /// wires the call at the correct slot in the turn sequence.
 pub fn process_healing_phase(state: &mut GameState) {
-    for player in &mut state.players {
+    // Snapshot every unit's (owner, tile) up front so city healing can skip
+    // BESIEGED cities — a city with an enemy unit on its tile is under siege and
+    // must NOT heal (else end-of-turn healing would undo the same turn's siege
+    // damage, e.g. heal a 30-hp city to 50 before a 45-dmg siege resolves).
+    // Mirrors the live game's siege-suppress intent via real-time occupancy.
+    let unit_tiles: Vec<(usize, i32, i32)> = state
+        .players
+        .iter()
+        .enumerate()
+        .flat_map(|(pi, p)| p.units.iter().map(move |u| (pi, u.col, u.row)))
+        .collect();
+
+    for (pi, player) in state.players.iter_mut().enumerate() {
         // Snapshot city positions for garrison detection; `player` is borrowed
         // mutably below for units, so we can't hold a reference to
         // `player.city_positions` at the same time.
@@ -102,9 +114,17 @@ pub fn process_healing_phase(state: &mut GameState) {
             unit.hp = (unit.hp + heal_amount).min(unit.max_hp);
         }
 
-        // ── City healing ──────────────────────────────────────────────────
+        // ── City healing (siege-suppressed) ───────────────────────────────
-        for city in &mut player.cities {
+        for (ci, city) in player.cities.iter_mut().enumerate() {
             if city.hp > 0 && city.hp < city.max_hp {
+                let besieged = player.city_positions.get(ci).copied().is_some_and(|(cc, cr)| {
+                    unit_tiles
+                        .iter()
+                        .any(|&(opi, uc, ur)| opi != pi && uc == cc && ur == cr)
+                });
+                if besieged {
+                    continue; // under siege → no heal
+                }
                 city.hp = (city.hp + CITY_HEAL_PER_TURN).min(city.max_hp);
             }
         }
@@ -290,6 +310,42 @@ mod tests {
         );
     }
 
+    /// A city with an enemy unit on its tile is under siege and must NOT heal
+    /// (so end-of-turn healing can't undo the same turn's siege damage).
+    #[test]
+    fn besieged_city_does_not_heal() {
+        let mut p0 = PlayerState {
+            city_positions: vec![(3, 3)],
+            ..PlayerState::default()
+        };
+        let mut city = CityState::default();
+        city.hp = 80;
+        city.max_hp = 200;
+        p0.cities.push(city);
+
+        let mut p1 = PlayerState {
+            player_index: 1,
+            ..PlayerState::default()
+        };
+        p1.units.push(MapUnit {
+            col: 3,
+            row: 3,
+            hp: 60,
+            max_hp: 60,
+            ..MapUnit::default()
+        });
+
+        let mut state = GameState::default();
+        state.players.push(p0);
+        state.players.push(p1);
+        process_healing_phase(&mut state);
+
+        assert_eq!(
+            state.players[0].cities[0].hp, 80,
+            "besieged city (enemy unit on tile) must not heal"
+        );
+    }
+
     /// A city at max HP does not overheal.
     #[test]
     fn full_hp_city_is_not_overhealed() {