fixup(langgraph): canonical regenerate JSDoc to unblock api-docs gate (#208)

PR #207 merged with admin override while CI's stale-api-docs gate was
red — the gate is now red on main. The shorter JSDoc on
LangGraphAgent.regenerate (added in #207) caused TypeDoc to emit a
description that diverges from the committed agent/api/api-docs.json.

Match the canonical text from libs/chat/src/lib/agent/agent.ts:38-46
so the regenerated docs are byte-identical to what's already on main.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: blove

libs/langgraph/src/lib/agent.types.ts

@@ -312,11 +312,13 @@ export interface LangGraphAgent<T = unknown, ResolvedBag extends BagTemplate = B
   reload: () => void;
 
   /**
-   * Truncate the thread at the given assistant-message index and re-submit the
-   * preceding user message. Used by `<ngaf-chat>`'s regenerate action and any
-   * custom UI that wants the same semantics. Rejects if the agent is currently
-   * loading, if the index does not point at an assistant message, or if no
-   * preceding user message exists.
+   * Discards the assistant message at the given index AND all messages after
+   * it, then re-runs the agent against the trimmed conversation tail. The
+   * preceding user message (at index - 1) is preserved and re-submitted as
+   * the agent's input. No new user message is added to the history.
+   *
+   * Throws if the message at `index` is not 'assistant' role, or if the
+   * agent is currently loading another response.
    */
   regenerate: (assistantMessageIndex: number) => Promise<void>;