Release v4.58.0

Added

• Models can declare named external systems and reusable operations, or declare an operation inline with produces operation. Operations describe typed inputs, the system they use, and optional execution and compensation intent using existing files, code blocks and implementation hints (part of #301)
• Specifications can describe operation failure fixtures, requested operations and compensation expectations. Both compilers validate and print the new syntax; executable binding rejects it with PLAY0268 until operation semantics are supported (part of #301)
• Monaco and VS Code provide operation-aware completion, hover, highlighting, diagnostics and navigation without treating operations as events or giving them event destinations (part of #301)
• MCP exposes revision-pinned systems, operation contracts, ordered productions and phase intent for inspection and typed authoring. The event model board presents readable operation intent without inventing event cards or execution results (part of #301)

Changed

• Operation authoring documentation explains the syntax-only boundary, current supported surfaces and manual promotion from inline to standalone declarations. Execution and automatic operation refactoring remain unavailable (part of #301)