feat(tui): add /history command — M1-007 (#297)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

packages/cli/src/tui/commands/local/history.ts

@@ -0,0 +1,53 @@
+import type { ConversationMessage } from '../../gateway-api.js';
+
+const CONTEXT_WINDOW = 200_000;
+const CHARS_PER_TOKEN = 4;
+
+function estimateTokens(messages: ConversationMessage[]): number {
+  const totalChars = messages.reduce((sum, m) => sum + (m.content?.length ?? 0), 0);
+  return Math.round(totalChars / CHARS_PER_TOKEN);
+}
+
+export interface HistoryContext {
+  conversationId: string | undefined;
+  conversationTitle?: string | null;
+  gatewayUrl: string;
+  sessionCookie: string | undefined;
+  fetchMessages: (
+    gatewayUrl: string,
+    sessionCookie: string,
+    conversationId: string,
+  ) => Promise<ConversationMessage[]>;
+}
+
+export async function executeHistory(ctx: HistoryContext): Promise<string> {
+  const { conversationId, conversationTitle, gatewayUrl, sessionCookie, fetchMessages } = ctx;
+
+  if (!conversationId) {
+    return 'No active conversation.';
+  }
+
+  if (!sessionCookie) {
+    return 'Not authenticated — cannot fetch conversation messages.';
+  }
+
+  const messages = await fetchMessages(gatewayUrl, sessionCookie, conversationId);
+
+  const userMessages = messages.filter((m) => m.role === 'user').length;
+  const assistantMessages = messages.filter((m) => m.role === 'assistant').length;
+  const totalMessages = messages.length;
+
+  const estimatedTokens = estimateTokens(messages);
+  const contextPercent = Math.round((estimatedTokens / CONTEXT_WINDOW) * 100);
+
+  const label = conversationTitle ?? conversationId;
+
+  const lines = [
+    `Conversation: ${label}`,
+    `Messages: ${totalMessages} (${userMessages} user, ${assistantMessages} assistant)`,
+    `Estimated tokens: ~${estimatedTokens.toLocaleString()}`,
+    `Context usage: ~${contextPercent}% of ${(CONTEXT_WINDOW / 1000).toFixed(0)}K`,
+  ];
+
+  return lines.join('\n');
+}