From d67c4b3059ceee93c134c9132bb2203566b8bd71 Mon Sep 17 00:00:00 2001
From: aiongg <aiongtaigi@gmail.com>
Date: Thu, 22 Oct 2026 21:41:50 +0000
Subject: [PATCH] fix(js): an XFA value past the effect cap leaves the field
 unchanged

---
 crates/js/src/tests.rs | 15 +++++++++++++++
 crates/js/src/xfa.rs   |  4 ++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/crates/js/src/tests.rs b/crates/js/src/tests.rs
index 07f04614d..01a436240 100644
--- a/crates/js/src/tests.rs
+++ b/crates/js/src/tests.rs
@@ -723,6 +723,21 @@ mod xfa_model {
         assert!(!o.effects.iter().any(|e| matches!(e, XfaEffect::SetPresence { som, .. } | XfaEffect::SetAccess { som, .. } if som.contains("qty"))));
     }
 
+    /// Past the effect cap, a value written to a field with no effect yet is left out of reads as
+    /// well as the effects; a field written again before the cap still takes its new value.
+    #[test]
+    fn a_value_past_the_effect_cap_is_left_out_of_reads_and_effects_alike() {
+        let o = go(
+            "price.rawValue = 1; for (var i = 0; i < 20000; i++) xfa.host.beep(); qty.rawValue = 9; price.rawValue = 3; qty.rawValue + ':' + price.rawValue",
+            "form1[0].page1[0]",
+            "click",
+        );
+        assert_eq!(o.error, None, "{o:?}");
+        assert_eq!(o.effects.len(), MAX_EFFECTS);
+        assert_eq!(o.result.as_deref(), Some("4:3"));
+        assert!(!o.effects.iter().any(|e| matches!(e, XfaEffect::SetValue { som, .. } if som.contains("qty"))));
+    }
+
     #[test]
     fn urls_and_reset_lists_are_clipped_and_deduplicated() {
         let o = go(
diff --git a/crates/js/src/xfa.rs b/crates/js/src/xfa.rs
index 18013e001..8a60e8ba9 100644
--- a/crates/js/src/xfa.rs
+++ b/crates/js/src/xfa.rs
@@ -459,9 +459,9 @@ impl XHost {
             self.clipped_values += 1;
         }
         // The snapshot's copy and the effect's are charged together, before either is kept:
-        // past the byte budget the write is left out of both.
+        // past the byte budget or the effect cap the write is left out of both.
         let effect = XfaEffect::SetValue { som, value: text.clone() };
-        if !self.room(text.len().saturating_add(payload(&effect))) {
+        if !self.reserve(&effect, text.len().saturating_add(payload(&effect))) {
             return true;
         }
         if let Some(n) = self.nodes.get_mut(i) {