From 152facee0a04d5824bcb844c1fb053aef3b7562b Mon Sep 17 00:00:00 2001
From: Natalie <natalie@lilithuwu.com>
Date: Tue, 28 Apr 2026 00:10:30 -0400
Subject: [PATCH] =?UTF-8?q?fix(@projects/magic-civilization):=20?=
 =?UTF-8?q?=F0=9F=90=9B=20preserve=20border-expansion=20timing=20with=20mo?=
 =?UTF-8?q?difier?=
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Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>
---
 src/simulator/api-gdext/src/lib.rs | 33 ++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/src/simulator/api-gdext/src/lib.rs b/src/simulator/api-gdext/src/lib.rs
index d133b0c1..c630f0b5 100644
--- a/src/simulator/api-gdext/src/lib.rs
+++ b/src/simulator/api-gdext/src/lib.rs
@@ -1385,20 +1385,31 @@ impl GdCity {
         self.inner.process_culture(&ty)
     }
 
-    /// Process culture accumulation with a percentage modifier added to the
-    /// raw culture gain. `total_pct` is the SUM of all percentage bonuses
-    /// (cult_pct + border_pct + difficulty_culture_mult - 1.0). Rust owns
-    /// both the raw gain and the percent-bonus application — no GDScript-side
-    /// post-call adjustment needed (warcouncil p1-39 Rail-1 port, 2026-04-27).
-    /// Returns true if border expansion is ready post-bonus.
+    /// Process culture accumulation with a percentage modifier on the gained
+    /// culture. Mirrors the original GDScript flow exactly to preserve
+    /// border-expansion timing parity:
+    ///   1. Run base process_culture (raw gain added, can_expand evaluated)
+    ///   2. Add EXTRA gain = raw_gain × total_pct (matches the GDScript
+    ///      `set_culture_stored(post + gained * total_pct)` pattern)
+    /// `total_pct` is the SUM of all percentage bonuses
+    /// (cult_pct + border_pct + difficulty_culture_mult - 1.0).
+    /// Returns true if border expansion is ready (post-bonus). Warcouncil
+    /// p1-39 Rail-1 port, 2026-04-27 — preserves seed-determinism vs the
+    /// pre-port GDScript caller.
     #[func]
     fn process_culture_with_modifier(&mut self, tile_yields_json: GString, total_pct: f64) -> bool {
         let ty = Self::parse_tile_yields(&tile_yields_json.to_string());
-        let yields = self.inner.get_yields(&ty);
-        let raw_gain = yields.culture;
-        let scaled_gain = raw_gain * (1.0 + total_pct.max(-1.0));
-        self.inner.culture_stored += scaled_gain;
-        self.inner.can_expand()
+        let pre = self.inner.culture_stored;
+        let mut can_expand = self.inner.process_culture(&ty);
+        if total_pct > 0.0 {
+            let post = self.inner.culture_stored;
+            let raw_gain = post - pre;
+            if raw_gain > 0.0 {
+                self.inner.culture_stored = post + raw_gain * total_pct;
+                can_expand = self.inner.can_expand();
+            }
+        }
+        can_expand
     }
 
     /// Add production production.