Packages that exist to serve development, testing, and the examples rather than to ship as product API. They are real workspace packages (typed, tested, under the coverage gate), but they carry lower compatibility expectations: they may change or be removed when the development need behind them does, without the deprecation care a product package would warrant.

Package	Role	ctx key
`acp-snapshot/`	ACP test kit: shared subprocess/client launcher + snapshot harness, normalizers, and suite factory	(library — imported by ACP e2e and `*.snapshot.ts` suites)
`invariants/`	Dev-mode event-contract assertions	(listens on `session/`, `agent/`)
`llm-replay/`	Record/replay adapter: short-circuits `llm/stream` from a recorded session JSONL (keyless snapshot tests)	(listens on `llm/stream`)
`subagent-mock/`	Scripted `SubagentProvider` for deterministic seam/tool tests	(registers on `ctx.subagents`)

invariants runs only in dev mode (contract checks, not runtime behavior). llm-replay backs the demos and the snapshot test tier under the per-file coverage gate. acp-snapshot carries the ACP subprocess/client boundary plus the snapshot harness, normalizers, and suite machinery, so e2e tests share one launcher and every snapshot suite is a scenario table over one gate-covered implementation. subagent-mock exercises the real ctx.subagents load path without a model or child agent. A package graduates OUT of support/ into a product group only when it gains documented product consumers.