feat(setup): default to interactive Claude handoff on failure

Failures now launch an interactive Claude session instead of the
non-interactive assist (REASON/COMMAND parser). The user debugs
with full terminal access and types /exit to return to setup.

The original assist mode is available via --assist-mode flag or
NANOCLAW_SETUP_ASSIST_MODE=1 env var.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

setup/lib/claude-handoff.ts

@@ -23,10 +23,19 @@
  * attempting to parse it as a real answer.
  */
 import { execSync, spawn } from 'child_process';
+import path from 'path';
 
 import * as p from '@clack/prompts';
 import k from 'kleur';
 
+import {
+  type AssistContext,
+  BIG_PICTURE_FILES,
+  ensureClaudeReady,
+  offerClaudeAssist,
+  STEP_FILES,
+} from './claude-assist.js';
+import { ensureAnswer } from './runner.js';
 import { brandBody, note } from './theme.js';
 
 export interface HandoffContext {
@@ -194,3 +203,110 @@ function buildSystemPrompt(ctx: HandoffContext): string {
 
   return lines.join('\n');
 }
+
+/**
+ * Dispatcher: checks NANOCLAW_SETUP_ASSIST_MODE and delegates to either
+ * the interactive failure handoff (default) or the non-interactive assist.
+ *
+ * Drop-in replacement for `offerClaudeAssist` at failure call sites.
+ */
+export async function offerClaudeOnFailure(
+  ctx: AssistContext,
+  projectRoot: string = process.cwd(),
+): Promise<boolean> {
+  if (process.env.NANOCLAW_SETUP_ASSIST_MODE === 'true' || process.env.NANOCLAW_SETUP_ASSIST_MODE === '1') {
+    return offerClaudeAssist(ctx, projectRoot);
+  }
+  return offerFailureHandoff(ctx, projectRoot);
+}
+
+/**
+ * Interactive Claude handoff for setup failures. Same role as
+ * `offerClaudeAssist` but spawns an interactive session instead of
+ * parsing a structured REASON/COMMAND response.
+ *
+ * Returns `true` if Claude was launched (the user may have fixed
+ * things during the session), `false` if skipped/declined/unavailable.
+ */
+async function offerFailureHandoff(
+  ctx: AssistContext,
+  projectRoot: string,
+): Promise<boolean> {
+  if (process.env.NANOCLAW_SKIP_CLAUDE_ASSIST === '1') return false;
+  if (!(await ensureClaudeReady(projectRoot))) return false;
+
+  const want = ensureAnswer(
+    await p.confirm({
+      message: 'Want to debug this with Claude?',
+      initialValue: true,
+    }),
+  );
+  if (!want) return false;
+
+  const systemPrompt = buildFailureSystemPrompt(ctx, projectRoot);
+
+  note(
+    [
+      "Launching Claude to help debug this failure.",
+      "It has the context of what went wrong.",
+      "",
+      k.dim("Type /exit (or press Ctrl-D) when you're ready to come back to setup."),
+    ].join('\n'),
+    'Handing off to Claude',
+  );
+
+  return new Promise<boolean>((resolve) => {
+    const child = spawn(
+      'claude',
+      [
+        '--append-system-prompt',
+        systemPrompt,
+        '--permission-mode',
+        'acceptEdits',
+      ],
+      { stdio: 'inherit' },
+    );
+    child.on('close', () => {
+      p.log.success(brandBody("Back from Claude. Let's continue."));
+      resolve(true);
+    });
+    child.on('error', () => {
+      p.log.error("Couldn't launch Claude. Continuing without handoff.");
+      resolve(false);
+    });
+  });
+}
+
+function buildFailureSystemPrompt(ctx: AssistContext, projectRoot: string): string {
+  const stepRefs = STEP_FILES[ctx.stepName] ?? [];
+  const references = [
+    ...BIG_PICTURE_FILES,
+    ...stepRefs,
+    'logs/setup.log',
+    ctx.rawLogPath
+      ? path.relative(projectRoot, ctx.rawLogPath)
+      : 'logs/setup-steps/',
+  ].filter((v, i, a) => a.indexOf(v) === i);
+
+  const lines: string[] = [
+    "The user is running NanoClaw's interactive setup flow and hit a failure.",
+    '',
+    `Failed step: ${ctx.stepName}`,
+    `Error: ${ctx.msg}`,
+  ];
+
+  if (ctx.hint) lines.push(`Hint: ${ctx.hint}`);
+
+  lines.push(
+    '',
+    'Your job: help them diagnose and fix this issue. Read the referenced files',
+    'and logs to understand what went wrong, then help them fix it. You can read',
+    'files, run commands, check logs, and explain what happened. Be concise.',
+    "When they're ready to resume setup, tell them to type /exit.",
+    '',
+    'Relevant files (read as needed with the Read tool):',
+  );
+  for (const f of references) lines.push(`  - ${f}`);
+
+  return lines.join('\n');
+}