feat: experimental sub-agent API and examples

[threepointone]

Adds a first-class sub-agent abstraction for spawning child Durable Objects (facets) with isolated SQLite from a parent Agent.

What

• SubAgent base class — extends partyserver's Server, provides subAgent(), abortSubAgent(), deleteSubAgent()
• withSubAgents() mixin — adds sub-agent methods to Agent, AIChatAgent, McpAgent, etc. without shipping them in the base class
• SubAgentStub<T> — typed RPC stubs that expose user-defined methods while hiding Server/DO internals
• RFC — design/rfc-sub-agents.md documenting the problem, proposal, alternatives, patterns, and open questions

Examples updated

All four experimental/gadgets-* examples now use the sub-agent API:

• gadgets-subagents — fan-out/fan-in with parallel LLM calls across three perspective sub-agents
• gadgets-chat — multi-room chat via ChatRoom sub-agents with isolated message history
• gadgets-sandbox — CustomerDatabase as a sub-agent for data isolation in a code sandbox
• gadgets-gatekeeper — gated database access enforced structurally via sub-agent boundary

Exported from

import { SubAgent, withSubAgents } from "agents/experimental/subagent";

Requires the "experimental" compatibility flag in wrangler.jsonc.

[changeset-bot]

⚠️ No Changeset found

Latest commit: c3c8774

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/agents@1060

npm i https://pkg.pr.new/@cloudflare/ai-chat@1060

npm i https://pkg.pr.new/@cloudflare/codemode@1060

npm i https://pkg.pr.new/hono-agents@1060

commit: 733ef05