POC: F5 launch config, README, and implementation plan (Feature #2)

.vscode launch/tasks wire F5 -> Run Extension (preLaunchTask: npm build).
README documents run/dev. Plan archived under docs/superpowers/plans/.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

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+# vscode-cowriting-plugin
+
+Non-shippable **proof-of-concept** (Feature #2 of Epic #1): a standalone VS Code
+extension that drives **[`@cline/sdk`](https://www.npmjs.com/package/@cline/sdk)**
+— validating Approach A (own coauthoring extension on the Cline SDK, no fork).
+
+## What it does
+
+Registers one command, **`Cowriting: Show Cline SDK Info`**, which loads
+`@cline/sdk` and shows the SDK build version plus the agent's builtin tool
+catalog (a pure, key-free SDK call) in a notification and the
+"Cowriting (Cline SDK)" output channel.
+
+## Architecture
+
+- CommonJS extension bundled with esbuild (`src/extension.ts` → `out/extension.cjs`).
+- `@cline/sdk` is ESM-only (Node ≥22) and uses `createRequire(import.meta.url)`,
+  so it is **not** bundled — it is shipped in `node_modules` and loaded at
+  runtime via dynamic `import()` from the vscode-free `src/cline.ts`.
+
+## Run it (F5)
+
+1. `npm install`
+2. `npm run build`
+3. Press **F5** (or Run → "Run Extension") to launch the Extension Development Host.
+4. In the new window: **Cmd/Ctrl+Shift+P** → **"Cowriting: Show Cline SDK Info"**.
+
+## Develop
+
+- `npm run watch` — rebuild on change.
+- `npm test` — run the unit test for the SDK driver.
+- `npm run typecheck` — type-check without emit.