The code-execution capability seam (see capability seams): an abstract runtime interface for executing one model-written program against host-provided async bindings, capturing what it printed and returned. The consumer is the tool registry's Code Mode (tools: { mode: code } — the run_code tool and the generated TypeScript SDK); design in the Code Mode Agent Note. Product packages.

Package	Role	ctx key
`code-runtime/`	Abstract code-execution seam (interface + vocabulary)	`ctx.codeRuntime`
`code-runtime-worker/`	Worker-thread backend: fresh worker per run, TypeScript via host-side type-strip (annotations advisory, never type-checked), port-bridged bindings, budget/heap containment	registers `ctx.codeRuntime`
`code-runtime-e2b/`	E2B backend: host type-strip and bindings, fresh remote runner/worker, framed bridge, remote process-group cleanup	registers `ctx.codeRuntime`

Backends differ by execution substrate and source language—both readonly descriptors on the service—and register ctx.codeRuntime without touching the interface or its consumer. The E2B ownership split is recorded in the remote extension note.