test(ai-chat): cover role-pick autoStart logic + the rolePickedNoSend reset (#149 review)

Review of #156 (Request changes) flagged the new CLIENT logic as untested. Extract
the decision logic from chat-thread.tsx into pure, unit-testable helpers and cover
both branches the reviewer called out:

- `roleLaunchMessage(role, default)` — the three-way handleRolePick behavior:
  autoStart=false -> null (send nothing); autoStart=true + custom -> trimmed
  message; autoStart=true + empty/null/whitespace -> default fallback.
- `shouldResetRolePicked(chatId, roleId, flag)` — the #149 render-phase reset; the
  regression test asserts the stuck-flag case (New chat after an autoStart=false
  pick -> cards return) that the pre-fix code never handled, and that a still-bound
  role keeps the cards hidden.

chat-thread.tsx now calls these helpers (behavior unchanged). 9 new pure tests.

Also folded the review's cosmetic suggestion: `x ? x : null` -> `x || null` in
ai-agent-roles.repo.ts (identical for string|null|undefined).

Client tsc clean; role-launch + role-cards green; repo spec green.

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

apps/client/src/features/ai-chat/components/chat-thread.tsx

@@ -21,6 +21,10 @@ import {
   IAiChatMessageRow,
   IAiRole,
 } from "@/features/ai-chat/types/ai-chat.types.ts";
+import {
+  roleLaunchMessage,
+  shouldResetRolePicked,
+} from "@/features/ai-chat/utils/role-launch.ts";
 import { describeChatError } from "@/features/ai-chat/utils/error-message.ts";
 import { extractServerChatId } from "@/features/ai-chat/utils/adopt-chat-id.ts";
 import {
@@ -330,13 +334,14 @@ export default function ChatThread({
   const handleRolePick = (role: IAiRole): void => {
     roleIdRef.current = role.id;
     onRolePicked?.(role);
-    if (role.autoStart) {
-      // Custom launch message when set; otherwise the built-in default text.
-      sendMessage({
-        text: role.launchMessage?.trim() || t("Take a look at the current document"),
-      });
+    const launch = roleLaunchMessage(
+      role,
+      t("Take a look at the current document"),
+    );
+    if (launch !== null) {
+      sendMessage({ text: launch });
     } else {
-      // Bind only: hide the cards and show the composer, send nothing.
+      // autoStart=false -> bind only: hide the cards, show the composer.
       setRolePickedNoSend(true);
     }
   };
@@ -348,7 +353,7 @@ export default function ChatThread({
   // correctly stay hidden then. Render-phase reset (React "adjust state on prop
   // change"): one-shot — it re-renders with the flag false and the guard no longer
   // matches, so it cannot loop. (Review of #149.)
-  if (chatId === null && roleId == null && rolePickedNoSend) {
+  if (shouldResetRolePicked(chatId, roleId, rolePickedNoSend)) {
     setRolePickedNoSend(false);
   }
   const showRoleCards =