Flue

What's Peculiar

• Orthogonal component: in-memory virtual sandbox by default. First framework to invert the hierarchy — default to a virtual sandbox (just-bash, in-memory) instead of a container per agent. Full container (@cloudflare/sandbox) is opt-in, requested explicitly. 100x faster startup, zero idle cost, scales to millions of concurrent agents. Most frameworks assume Docker from the start.
• Isolation boundary: Prompt/process-level by default. The default isolation line sits at the process/virtual-sandbox layer (just-bash, in-memory), NOT a container per agent. Container isolation (@cloudflare/sandbox) is opt-in only. The trade-off vs container-per-agent frameworks: faster, cheaper, higher per-agent scale; weaker isolation. You move the boundary up only when you ask for it.
• Durable execution / crash recovery. Mid-2026 added a recovery layer: on resume the runtime reconciles persisted submission state and repairs partial tool-result batches (repair-on-resume, not replay), with typed FlueError terminalization, expired-lease node reconciliation, and evaluate-then-start turn recovery. Docs document the semantics plus a best-effort ?wait=result / submission_settled event.
• Durable Objects session persistence. On Cloudflare Workers, session state auto-persists via Durable Objects (SQLite per session). No external database, no manual serialization. Sessions survive across requests without code. Hibernates when idle.
• Sandbox tiering. Explicit levels: virtual (default, in-memory) → local (CI, host filesystem) → container (full Linux, opt-in). Choose per agent based on needs. No other framework offers this hierarchy.
• Runtime-agnostic build. Same agent code deploys to Node.js (single bundled .mjs) and Cloudflare (Workers + Durable Objects) via adapters. Not a technical innovation (Astro/Next.js do this), but applied to agents.

What's NOT novel: Schema validation (MCP reinvention), Markdown skills (industry pattern), Workers deployment (Cloudflare has cloudflare/agents), MCP integration (standard protocol).