Release v4.57.0

Added

• Command handlers can describe implementation intent with an implementation block containing ordered hint strings and an optional existing file or fenced-code source. Hints-only blocks represent pending implementation; existing direct attachment forms remain supported (part of #307)
• MCP exposes a revision-pinned handler-intent inventory showing pending, file-backed and inline handlers, their hints and identity status. Inspection works without a successful executable model and refuses ambiguous ownership instead of choosing a scope (part of #307)
• Both compilers, typed authoring, Monaco and VS Code support handler implementation blocks, with documentation and an Invoicing example. Handler execution remains unsupported; no AI runs during builds (part of #307)

Fixed

• Workspace indexing retains scoped import placement, so imported handlers remain visible. Hierarchy renames, optionality repairs and produced-event mapping edits retain the resolved placement and original source formatting.