POST /api/v1/ai-sessions and friends call _require_ai_enabled(), which returns 503 when no provider key is set. The new prefill-handoff regression test (e2e/assistant-chat-prefill.spec.ts) drives the dashboard prefill flow, which has to create a chat session before its page.route stub on /chat can fire — so without a key, session creation 503s and the test never sees the task lane. The Playwright stub intercepts /chat in the browser, so the backend never actually contacts Anthropic — but the AI-enabled gate still needs to pass. A stub value is enough. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>