feat(chat): print agent + system prompt banner at chat start

When you launch \`mcpctl chat <agent>\` it's not always obvious which
agent, LLM, project, or system prompt you're actually wired to,
especially when --system / --system-append flags are layered on top
of the agent's defaults. The session would just start at \`> \` with
no confirmation of the configuration.

Now both REPL and one-shot modes print a banner to stderr listing:
  - agent name + description
  - LLM + project (if attached)
  - effective system prompt (or --system override) and any
    --system-append addendum, indented for readability
  - active sampling overrides (temperature, top_p, etc.)

Goes through stderr so \`mcpctl chat ... -m "hi" 2>/dev/null\` keeps
piping clean. Best-effort: a metadata fetch failure logs and lets
the chat proceed rather than blocking.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/cli/src/commands/chat.ts

@@ -138,6 +138,7 @@ async function runOneShot(
   overrides: Overrides,
   stream: boolean | undefined,
 ): Promise<void> {
+  await printChatHeader(deps, agent, overrides);
   if (stream === false) {
     const body: Record<string, unknown> = { message, ...overrides };
     if (threadId !== undefined) body.threadId = threadId;
@@ -170,12 +171,14 @@ async function runRepl(
   const rl = readline.createInterface({ input: process.stdin, output: process.stdout });
   const ask = (q: string): Promise<string> => new Promise((resolve) => rl.question(q, resolve));
 
+  await printChatHeader(deps, agent, overrides);
+
   // The status bar persists across turns inside a REPL — it shows the last
   // response's final rate between messages, then refreshes live during the
   // next stream. Only enabled for streaming mode (no rate to show otherwise).
   const bar = stream === false ? null : installStatusBar();
 
-  process.stderr.write(`Chat with agent '${agent}'. Slash commands: /set /system /tools /clear /save /quit. Ctrl-D to exit.\n`);
+  process.stderr.write(`Slash commands: /set /system /tools /clear /save /quit. Ctrl-D to exit.\n`);
   if (threadId !== undefined) {
     process.stderr.write(`(resuming thread ${threadId})\n`);
   }
@@ -660,6 +663,82 @@ function installStatusBar(): StatusBar | null {
   return { update, teardown };
 }
 
+interface AgentInfo {
+  name: string;
+  description: string;
+  systemPrompt: string;
+  llm: { name: string };
+  project: { name: string } | null;
+}
+
+/**
+ * Prints a startup banner showing what the chat session will be running with:
+ * agent name, LLM, project, the assembled system prompt, and any session
+ * overrides. Lets the user verify the wiring before they spend tokens.
+ *
+ * Best-effort: if the agent fetch fails we log and continue rather than
+ * blocking the chat — the user might still want to send a message.
+ */
+async function printChatHeader(
+  deps: ChatCommandDeps,
+  agent: string,
+  overrides: Overrides,
+): Promise<void> {
+  let info: AgentInfo;
+  try {
+    info = await deps.client.get<AgentInfo>(`/api/v1/agents/${encodeURIComponent(agent)}`);
+  } catch (err) {
+    process.stderr.write(`(could not fetch agent metadata: ${(err as Error).message})\n`);
+    return;
+  }
+
+  const sep = '─'.repeat(60);
+  const out = (s: string): void => { process.stderr.write(`${styleStats(s)}\n`); };
+  const indent = (text: string): string =>
+    text.split('\n').map((l) => `  ${l}`).join('\n');
+
+  out(sep);
+  out(`Agent: ${info.name}${info.description !== '' ? ` — ${info.description}` : ''}`);
+  const tail = info.project !== null ? `   Project: ${info.project.name}` : '';
+  out(`LLM: ${info.llm.name}${tail}`);
+
+  if (overrides.systemOverride !== undefined) {
+    out(`System prompt (--system replaces agent.systemPrompt):`);
+    out(indent(overrides.systemOverride));
+  } else {
+    out(`System prompt:`);
+    out(indent(info.systemPrompt !== '' ? info.systemPrompt : '(empty)'));
+  }
+  if (overrides.systemAppend !== undefined) {
+    out(`System append (--system-append):`);
+    out(indent(overrides.systemAppend));
+  }
+  if (info.project !== null) {
+    out(`(project prompts auto-appended at chat time; /tools lists MCP servers)`);
+  }
+
+  const sessionOverrides = describeSessionOverrides(overrides);
+  if (sessionOverrides !== '') {
+    out(`Sampling overrides: ${sessionOverrides}`);
+  }
+  out(sep);
+}
+
+function describeSessionOverrides(o: Overrides): string {
+  const parts: string[] = [];
+  if (o.temperature !== undefined) parts.push(`temperature=${String(o.temperature)}`);
+  if (o.top_p !== undefined) parts.push(`top_p=${String(o.top_p)}`);
+  if (o.top_k !== undefined) parts.push(`top_k=${String(o.top_k)}`);
+  if (o.max_tokens !== undefined) parts.push(`max_tokens=${String(o.max_tokens)}`);
+  if (o.seed !== undefined) parts.push(`seed=${String(o.seed)}`);
+  if (o.stop !== undefined && o.stop.length > 0) parts.push(`stop=${o.stop.join(',')}`);
+  if (o.tools_allowlist !== undefined) parts.push(`allow_tools=${o.tools_allowlist.join(',')}`);
+  if (o.extra !== undefined) {
+    for (const [k, v] of Object.entries(o.extra)) parts.push(`${k}=${String(v)}`);
+  }
+  return parts.join(' ');
+}
+
 function collect(value: string, prev: string[]): string[] {
   return [...prev, value];
 }