Release v6.8.0

Screens can now be part of the executable model. A UI builder for any stack can read what each screen shows, which commands it issues and where it leads, all keyed to the model's own identities, without Scene.

Added

• ESM v42: ExecutableScreens.Admit adds each screen's data, actions, navigation and layout to its slice. Data is keyed to query identities, actions to command identities with every input as a command property identity, and navigation to screen identities. A reference the executable model does not hold refuses admission with a reason that names the screen. See UI contract. (#1187)
• UiContractBuilder.For(ExecutableSemanticModel) reads the stack-neutral screenplay-ui/1 contract from an ESM v42 model alone. Its members match the ones read from the sources.
• screenplay export --screens writes the ESM v42 model with its screens, and MCP read-workspace with view: "executable-model" and screens: true pages it.
• Published JSON Schema esm-v42.schema.json.

Changed

• ESM 41.0 (graph handlers that iterate an event collection) is listed as released; 42.0 is the claimed, unreleased version.
• A toolbar button that opens another slice now names that slice's screen as its navigation target in the UI contract, so it can be resolved.