From cccb6b64c3f3a856cba92eec1c94433f5936c045 Mon Sep 17 00:00:00 2001
From: Richard Zink <Richard Zink>
Date: Fri, 6 Nov 2026 09:54:19 +0100
Subject: [PATCH] AI masters build only rooms and towers they have researched

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/ai.rs    | 11 ++++++++++-
 src/rival.rs | 31 +++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/src/ai.rs b/src/ai.rs
index 65c00ad..eb094d9 100644
--- a/src/ai.rs
+++ b/src/ai.rs
@@ -221,6 +221,10 @@ impl Game {
     // the next room of the build order, where there is free own floor for it
     fn ai_rooms(&mut self, cx: i32, cy: i32) {
         for &(room, w, h, n) in BUILD.iter() {
+            // only what this master has researched (the same rules as the player)
+            if !self.ai_knows(crate::ui::Tool::Room(room)) {
+                continue;
+            }
             let tiles = self.counts[room];
             if tiles >= (w * h) as usize * n {
                 continue;
@@ -236,6 +240,11 @@ impl Game {
         }
     }
 
+    // has this master researched the tool (rooms, towers)?
+    fn ai_knows(&self, tool: crate::ui::Tool) -> bool {
+        crate::ui::TOOLS.iter().position(|&t| t == tool).map_or(false, |i| self.tool_allowed(i))
+    }
+
     // a rectangle of own plain floor, as near the heart as possible (not right next to it)
     fn ai_free_rect(&self, cx: i32, cy: i32, w: i32, h: i32) -> Option<(i32, i32)> {
         let me = self.me;
@@ -260,7 +269,7 @@ impl Game {
     fn ai_towers(&mut self, d: usize, cx: i32, cy: i32) {
         let me = self.me;
         let mine = self.towers.iter().filter(|t| !t.hero && self.map.t[t.tile].owner == me).count();
-        if mine >= MAX_TOWERS[d] || self.gold < 1800.0 || self.counts[0] == 0 {
+        if mine >= MAX_TOWERS[d] || self.gold < 1800.0 || self.counts[0] == 0 || !self.ai_knows(crate::ui::Tool::Tower(TowerKind::Arrow)) {
             return;
         }
         let spot = (0..self.map.t.len()).filter(|&i| {
diff --git a/src/rival.rs b/src/rival.rs
index 89cd7d3..93afb44 100644
--- a/src/rival.rs
+++ b/src/rival.rs
@@ -600,6 +600,37 @@ mod tests {
         g
     }
 
+    #[test]
+    fn the_ai_partner_builds_only_what_is_researched() {
+        // the first missions of both co-op campaigns: no library, no forge yet
+        let doc = crate::editor::coop_campaign::coop_campaign();
+        let games = [
+            crate::campaign::start_editor_coop_mission(&doc.missions[0], 0, 77),
+            crate::campaign::start_coop_mission(crate::campaign::coop_mission_indexes()[0], None),
+        ];
+        let lib = crate::ui::TOOLS.iter().position(|&t| t == crate::ui::Tool::Room(4)).unwrap();
+        let forge = crate::ui::TOOLS.iter().position(|&t| t == crate::ui::Tool::Room(8)).unwrap();
+        for mut g in games {
+            g.coop = true;
+            assert!(g.start_match(&[0, 2], 0));
+            g.sync_ai_sides(&[2], 1);
+            g.end_match();
+            let mine_knows = (g.tool_allowed(lib), g.tool_allowed(forge));
+            for _ in 0..(10 * 60 * 20) {
+                g.update(0.05);
+            }
+            let owner = Owner::of_side(2);
+            let has = |k: Kind| g.map.t.iter().any(|t| t.kind == k && t.owner == owner);
+            if !mine_knows.0 {
+                assert!(!has(Kind::Library), "the partner has no library either");
+            }
+            if !mine_knows.1 {
+                assert!(!has(Kind::Forge), "the partner has no forge either");
+            }
+            assert!(has(Kind::Lair) || has(Kind::Treasury), "but builds what it knows");
+        }
+    }
+
     #[test]
     fn imps_take_ground_from_enemies_but_never_from_allies() {
         let mut g = offline_league_game();