The workflow seam: a model-written JavaScript orchestration script that fans out subagents at scale (phases, structured per-agent results, concurrency caps), modeled on Claude Code's dynamic workflows. A capability seam (see capability seams) in the bash shape: ONE engine implementation per context registers as ctx.workflows; the model-facing tool consumes it.

Package	Role	ctx key
`workflow/`	Abstract workflow seam: service base class + run vocabulary + `workflow/*` events	`ctx.workflows`
`workflow-workerthread/`	`node:worker_threads` engine: one worker per run; the script's vm context lives inside the worker, `agent()` bridges to `ctx.subagents` over the message port	(provides `ctx.workflows`)
`tool-workflow/`	Model-facing `workflow` tool over `ctx.workflows`	(registers on `ctx.tools`)

The interface lives at workflow/workflow/. The engine's agent() hook rides the subagent seam (any registered provider; the shipped examples use spawn), and agent({ schema }) rides the structured-output support the in-process backends implement. The worker thread isolates the SCRIPT — the host never blocks on it, and a cancelled run's post-grace termination is real — but it is NOT a security boundary; an isolated-vm/separate-process engine (actual sandboxing) swaps in behind the same interface if that ever matters.

The proposal, decisions, and deferred work: docs/rfc/implemented/feature/2026-07-05-dynamic-workflows.md.