test(ai-chat): cover the conditional assistant-name signature (#108)

Extract the shared assistant-name predicate (resolveAssistantName: trimmed name
or null) used by typing-indicator + message-item, and unit-test the branches
(name shown; whitespace-only -> 'AI agent' fallback; undefined -> fallback).
Behavior-identical (|| -> ?? since the helper returns null).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/src/features/ai-chat/components/message-item.tsx

@@ -5,6 +5,7 @@ import type { UIMessage } from "@ai-sdk/react";
 import ToolCallCard from "@/features/ai-chat/components/tool-call-card.tsx";
 import { ToolUiPart, isToolPart } from "@/features/ai-chat/utils/tool-parts.tsx";
 import { renderChatMarkdown } from "@/features/ai-chat/utils/markdown.ts";
+import { resolveAssistantName } from "@/features/ai-chat/utils/assistant-name.ts";
 import { describeChatError } from "@/features/ai-chat/utils/error-message.ts";
 import classes from "@/features/ai-chat/components/ai-chat.module.css";
 
@@ -67,7 +68,7 @@ export default function MessageItem({
   return (
     <Box className={classes.messageRow}>
       <Text size="xs" c="dimmed" mb={4}>
-        {assistantName?.trim() || t("AI agent")}
+        {resolveAssistantName(assistantName) ?? t("AI agent")}
       </Text>
       {message.parts.map((part, index) => {
         if (part.type === "text") {

apps/client/src/features/ai-chat/components/typing-indicator.tsx

@@ -1,5 +1,6 @@
 import { Box, Group, Text } from "@mantine/core";
 import { useTranslation } from "react-i18next";
+import { resolveAssistantName } from "@/features/ai-chat/utils/assistant-name.ts";
 import classes from "@/features/ai-chat/components/ai-chat.module.css";
 
 interface TypingIndicatorProps {
@@ -23,12 +24,12 @@ interface TypingIndicatorProps {
  */
 export default function TypingIndicator({ assistantName }: TypingIndicatorProps) {
   const { t } = useTranslation();
-  const name = assistantName?.trim();
+  const name = resolveAssistantName(assistantName);
 
   return (
     <Box className={classes.messageRow}>
       <Text size="xs" c="dimmed" mb={4}>
-        {name || t("AI agent")}
+        {name ?? t("AI agent")}
       </Text>
       <Group gap={8} align="center">
         <span className={classes.typingDots} aria-hidden="true">

apps/client/src/features/ai-chat/utils/assistant-name.test.ts

@@ -0,0 +1,24 @@
+import { describe, it, expect } from "vitest";
+import { resolveAssistantName } from "./assistant-name";
+
+describe("resolveAssistantName", () => {
+  it("returns a real name unchanged", () => {
+    expect(resolveAssistantName("Ada")).toBe("Ada");
+  });
+
+  it("trims surrounding whitespace from a real name", () => {
+    expect(resolveAssistantName("  Ada  ")).toBe("Ada");
+  });
+
+  it("returns null for a whitespace-only name (the reason for .trim())", () => {
+    expect(resolveAssistantName("   ")).toBeNull();
+  });
+
+  it("returns null when the name is undefined", () => {
+    expect(resolveAssistantName(undefined)).toBeNull();
+  });
+
+  it("returns null for an empty string", () => {
+    expect(resolveAssistantName("")).toBeNull();
+  });
+});

apps/client/src/features/ai-chat/utils/assistant-name.ts

@@ -0,0 +1,16 @@
+// Pure helper for resolving the assistant's display name. Kept free of React so
+// it can be unit-tested in isolation (see assistant-name.test.ts) and shared by
+// the components that render the assistant identity (TypingIndicator, MessageItem).
+
+/**
+ * Resolve the assistant's display name from the optional configured identity.
+ *
+ * Returns the trimmed name when it has visible (non-whitespace) characters, or
+ * `null` when the name is absent or whitespace-only. Callers fall back to a
+ * generic "AI agent" label on `null`. The `.trim()` is why a name of "   " must
+ * resolve to `null` rather than rendering an empty label.
+ */
+export function resolveAssistantName(assistantName?: string): string | null {
+  const name = assistantName?.trim();
+  return name ? name : null;
+}