feat(cli): print, draw and check the plan an extension compiles

CHANGELOG.md

@@ -63,6 +63,17 @@ Pre-1.0 releases followed it in spirit; their breaking changes are marked **Brea
   `PreflightError` is exported from the root, so the error can be recognised
   with `instanceof` rather than by its name.
 
+- **A command-line tool: `vscode-ext-kit plan`.** It reads the plan an
+  extension compiles at import time and prints it — as the JSON `describePlan`
+  returns, as a Mermaid or Graphviz graph of modules, services and the edges
+  between them, or, with `--check`, as an exit code and the list of problems
+  preflight found. The entry module is evaluated with a stand-in for `vscode`,
+  which only exists inside an extension host; that works because nothing in
+  this package touches VS Code before `activate`, and it holds an extension's
+  module-scope code to the rule the framework already asks of it. The tool
+  lives in `bin/` and is exercised by `verify:package` against the installed
+  tarball, not just the repository's own layout.
+
 ### Changed
 
 - **`defineExtension` is single-use, like the extension host it serves.** A

README.md

@@ -27,6 +27,7 @@ has stopped being obvious._
 - [Quick Start](#quick-start)
 - [Why vscode-ext-kit](#why-vscode-ext-kit)
 - [Usage](#usage)
+- [Command Line](#command-line)
 - [What Is Guaranteed](#what-is-guaranteed)
 - [Known Limitations](#known-limitations)
 - [How It Works](#how-it-works)
@@ -261,6 +262,27 @@ generated API reference is not built yet.
 
 ---
 
+## Command Line
+
+The package ships one command. It reads the plan an extension compiles at
+import time and prints it, so what the extension registers can be reviewed,
+diffed and drawn without starting VS Code.
+
+```bash
+npx vscode-ext-kit plan ./out/extension.js                    # the plan as JSON
+npx vscode-ext-kit plan ./out/extension.js --format mermaid   # modules, services and their edges
+npx vscode-ext-kit plan ./out/extension.js --check            # exit 1 with every problem preflight found
+```
+
+The entry module is evaluated with a stand-in for `vscode`, which only exists
+inside an extension host. That works because nothing in this package touches
+VS Code before `activate` — and it means module-scope code in the extension
+must not either, which the framework already asks for. Export the
+`defineExtension` result as `app` (or name the export with `--export`); the
+JSON is what `describePlan` returns.
+
+---
+
 ## What Is Guaranteed
 
 - `stop()` runs exactly once, and only after `start()` completed or failed