diff --git a/internal/runtime/executor/helps/codex_input_ids.go b/internal/runtime/executor/helps/codex_input_ids.go
index 1ee2bac4..05c011e9 100644
--- a/internal/runtime/executor/helps/codex_input_ids.go
+++ b/internal/runtime/executor/helps/codex_input_ids.go
@@ -12,10 +12,11 @@ import (
 )
 
 const (
-	codexInputItemIDLimit         = 64
-	codexMessageItemIDPrefix      = "msg"
-	codexReasoningItemIDPrefix    = "rs"
-	codexFunctionCallItemIDPrefix = "fc"
+	codexInputItemIDLimit           = 64
+	codexMessageItemIDPrefix        = "msg"
+	codexReasoningItemIDPrefix      = "rs"
+	codexFunctionCallItemIDPrefix   = "fc"
+	codexCustomToolCallItemIDPrefix = "ctc"
 )
 
 // SanitizeCodexInputItemIDs normalizes supported input item IDs for Codex, removes encrypted
@@ -103,6 +104,8 @@ func normalizeCodexInputItemID(item gjson.Result, id string) string {
 		prefix = codexReasoningItemIDPrefix
 	case "function_call":
 		prefix = codexFunctionCallItemIDPrefix
+	case "custom_tool_call":
+		prefix = codexCustomToolCallItemIDPrefix
 	default:
 		return id
 	}
diff --git a/internal/runtime/executor/helps/codex_input_ids_test.go b/internal/runtime/executor/helps/codex_input_ids_test.go
index c9f4434e..ba9cb92f 100644
--- a/internal/runtime/executor/helps/codex_input_ids_test.go
+++ b/internal/runtime/executor/helps/codex_input_ids_test.go
@@ -94,6 +94,16 @@ func TestSanitizeCodexInputItemIDsNormalizesResponseItemIDs(t *testing.T) {
 	}
 }
 
+func TestSanitizeCodexInputItemIDsNormalizesCustomToolCallIDs(t *testing.T) {
+	const invalidID = "item_44e13caebc1ddf25f1337cbe"
+	body := []byte(`{"input":[{"type":"custom_tool_call","id":"` + invalidID + `","call_id":"call-1","name":"lookup","input":"{}"}]}`)
+
+	got := SanitizeCodexInputItemIDs(body)
+	if actual := gjson.GetBytes(got, "input.0.id").String(); actual != "ctc_"+invalidID {
+		t.Fatalf("custom_tool_call ID = %q, want ctc-prefixed ID", actual)
+	}
+}
+
 func TestSanitizeCodexInputItemIDsDropsOverlongEncryptedReasoningItem(t *testing.T) {
 	longReasoningID := "rs_" + strings.Repeat("a", 64)
 	shortReasoningID := "rs_" + strings.Repeat("b", 48)