diff --git a/internal/adapter/openai/tool_sieve_state.go b/internal/adapter/openai/tool_sieve_state.go
index f36560a..60370e9 100644
--- a/internal/adapter/openai/tool_sieve_state.go
+++ b/internal/adapter/openai/tool_sieve_state.go
@@ -34,7 +34,8 @@ type toolCallDelta struct {
 	Arguments string
 }
 
-const toolSieveContextTailLimit = 256
+// Keep in sync with JS TOOL_SIEVE_CONTEXT_TAIL_LIMIT.
+const toolSieveContextTailLimit = 2048
 
 func (s *toolStreamSieveState) resetIncrementalToolState() {
 	s.disableDeltas = false
diff --git a/internal/js/helpers/stream-tool-sieve/state.js b/internal/js/helpers/stream-tool-sieve/state.js
index df82404..9a5b1c3 100644
--- a/internal/js/helpers/stream-tool-sieve/state.js
+++ b/internal/js/helpers/stream-tool-sieve/state.js
@@ -1,6 +1,7 @@
 'use strict';
 
-const TOOL_SIEVE_CONTEXT_TAIL_LIMIT = 256;
+// Keep in sync with Go toolSieveContextTailLimit.
+const TOOL_SIEVE_CONTEXT_TAIL_LIMIT = 2048;
 
 function createToolSieveState() {
   return {