Provides the V8 execution machinery shared by plugin guests and persistent JavaScript REPLs. plugin implements bounded guest execution; repl and CodeExecutor support cells that retain variables between calls. Embeddings supply callable capabilities and own their resources. A JavaScript promise finishing does not prove that the native work it started has settled.
Nested tool calls pass complete JSON inputs and results through the embedding's original executor. A cell can consume a large tool result and publish a short summary; complete cell results, emitted output and scratch values remain available under the configured V8 heap and execution deadline. Admitted tool work remains tracked until cleanup, including when JavaScript stops observing its promise.