fix: detect loose functionCall keys in tool sieve

internal/adapter/openai/tool_sieve_functioncall.go

@@ -4,7 +4,22 @@ import "strings"
 
 func findQuotedFunctionCallKeyStart(s string) int {
 	lower := strings.ToLower(s)
-	const key = "\"functioncall\""
+	quotedIdx := findFunctionCallKeyStart(lower, `"functioncall"`)
+	baretIdx := findFunctionCallKeyStart(lower, "functioncall")
+
+	switch {
+	case quotedIdx < 0:
+		return baretIdx
+	case baretIdx < 0:
+		return quotedIdx
+	case quotedIdx < baretIdx:
+		return quotedIdx
+	default:
+		return baretIdx
+	}
+}
+
+func findFunctionCallKeyStart(lower, key string) int {
 	for from := 0; from < len(lower); {
 		rel := strings.Index(lower[from:], key)
 		if rel < 0 {
@@ -15,6 +30,10 @@ func findQuotedFunctionCallKeyStart(s string) int {
 			from = idx + 1
 			continue
 		}
+		if !hasJSONKeyBoundary(lower, idx, len(key)) {
+			from = idx + 1
+			continue
+		}
 		j := idx + len(key)
 		for j < len(lower) && (lower[j] == ' ' || lower[j] == '\t' || lower[j] == '\r' || lower[j] == '\n') {
 			j++
@@ -30,3 +49,23 @@ func findQuotedFunctionCallKeyStart(s string) int {
 func hasJSONObjectContextPrefix(prefix string) bool {
 	return strings.LastIndex(prefix, "{") >= 0
 }
+
+func hasJSONKeyBoundary(s string, idx, keyLen int) bool {
+	if idx > 0 {
+		prev := s[idx-1]
+		if isLowerAlphaNumeric(prev) {
+			return false
+		}
+	}
+	if end := idx + keyLen; end < len(s) {
+		next := s[end]
+		if isLowerAlphaNumeric(next) {
+			return false
+		}
+	}
+	return true
+}
+
+func isLowerAlphaNumeric(b byte) bool {
+	return (b >= 'a' && b <= 'z') || (b >= '0' && b <= '9') || b == '_'
+}