diff --git a/internal/adapter/openai/tool_sieve_core.go b/internal/adapter/openai/tool_sieve_core.go
index 3d70551..1b3c975 100644
--- a/internal/adapter/openai/tool_sieve_core.go
+++ b/internal/adapter/openai/tool_sieve_core.go
@@ -282,32 +282,3 @@ func consumeToolCapture(state *toolStreamSieveState, toolNames []string) (prefix
 	prefixPart, suffixPart = trimWrappingJSONFence(prefixPart, suffixPart)
 	return prefixPart, parsed.Calls, suffixPart, true
 }
-
-func findQuotedFunctionCallKeyStart(s string) int {
-	lower := strings.ToLower(s)
-	const key = "\"functioncall\""
-	for from := 0; from < len(lower); {
-		rel := strings.Index(lower[from:], key)
-		if rel < 0 {
-			return -1
-		}
-		idx := from + rel
-		if !hasJSONObjectContextPrefix(lower[:idx]) {
-			from = idx + 1
-			continue
-		}
-		j := idx + len(key)
-		for j < len(lower) && (lower[j] == ' ' || lower[j] == '\t' || lower[j] == '\r' || lower[j] == '\n') {
-			j++
-		}
-		if j < len(lower) && lower[j] == ':' {
-			return idx
-		}
-		from = idx + 1
-	}
-	return -1
-}
-
-func hasJSONObjectContextPrefix(prefix string) bool {
-	return strings.LastIndex(prefix, "{") >= 0
-}
diff --git a/internal/adapter/openai/tool_sieve_functioncall.go b/internal/adapter/openai/tool_sieve_functioncall.go
new file mode 100644
index 0000000..f3cacbe
--- /dev/null
+++ b/internal/adapter/openai/tool_sieve_functioncall.go
@@ -0,0 +1,32 @@
+package openai
+
+import "strings"
+
+func findQuotedFunctionCallKeyStart(s string) int {
+	lower := strings.ToLower(s)
+	const key = "\"functioncall\""
+	for from := 0; from < len(lower); {
+		rel := strings.Index(lower[from:], key)
+		if rel < 0 {
+			return -1
+		}
+		idx := from + rel
+		if !hasJSONObjectContextPrefix(lower[:idx]) {
+			from = idx + 1
+			continue
+		}
+		j := idx + len(key)
+		for j < len(lower) && (lower[j] == ' ' || lower[j] == '\t' || lower[j] == '\r' || lower[j] == '\n') {
+			j++
+		}
+		if j < len(lower) && lower[j] == ':' {
+			return idx
+		}
+		from = idx + 1
+	}
+	return -1
+}
+
+func hasJSONObjectContextPrefix(prefix string) bool {
+	return strings.LastIndex(prefix, "{") >= 0
+}