Handle variable-length markdown fences in toolcall parser

internal/toolcall/toolcalls_parse.go

@@ -124,19 +124,40 @@ func stripFencedCodeBlocks(text string) string {
 }
 
 func parseFenceOpen(line string) (string, bool) {
-	if strings.HasPrefix(line, "```") {
-		return "```", true
+	if len(line) < 3 {
+		return "", false
 	}
-	if strings.HasPrefix(line, "~~~") {
-		return "~~~", true
+	ch := line[0]
+	if ch != '`' && ch != '~' {
+		return "", false
 	}
-	return "", false
+	count := countLeadingFenceChars(line, ch)
+	if count < 3 {
+		return "", false
+	}
+	return strings.Repeat(string(ch), count), true
 }
 
 func isFenceClose(line, marker string) bool {
-	if marker == "" || !strings.HasPrefix(line, marker) {
+	if marker == "" {
 		return false
 	}
-	rest := strings.TrimSpace(strings.TrimPrefix(line, marker))
+	ch := marker[0]
+	if line == "" || line[0] != ch {
+		return false
+	}
+	count := countLeadingFenceChars(line, ch)
+	if count < len(marker) {
+		return false
+	}
+	rest := strings.TrimSpace(line[count:])
 	return rest == ""
 }
+
+func countLeadingFenceChars(line string, ch byte) int {
+	count := 0
+	for count < len(line) && line[count] == ch {
+		count++
+	}
+	return count
+}

internal/toolcall/toolcalls_test.go

@@ -474,3 +474,14 @@ func TestParseToolCallsParsesOnlyNonFencedXMLToolCall(t *testing.T) {
 		t.Fatalf("expected non-fenced tool call to be parsed, got %#v", res.Calls[0])
 	}
 }
+
+func TestParseToolCallsParsesAfterFourBacktickFence(t *testing.T) {
+	text := "````markdown\n```xml\n<tool_call><tool_name>read_file</tool_name><parameters>{\"path\":\"README.md\"}</parameters></tool_call>\n```\n````\n<tool_call><tool_name>search</tool_name><parameters>{\"q\":\"outside\"}</parameters></tool_call>"
+	res := ParseToolCallsDetailed(text, []string{"read_file", "search"})
+	if len(res.Calls) != 1 {
+		t.Fatalf("expected exactly one parsed call outside four-backtick fence, got %#v", res.Calls)
+	}
+	if res.Calls[0].Name != "search" {
+		t.Fatalf("expected non-fenced tool call to be parsed, got %#v", res.Calls[0])
+	}
+}