diff --git a/.vscode/launch.json b/.vscode/launch.json
new file mode 100644
index 0000000..d91aabb
--- /dev/null
+++ b/.vscode/launch.json
@@ -0,0 +1,13 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Run Extension",
+      "type": "extensionHost",
+      "request": "launch",
+      "args": ["--extensionDevelopmentPath=${workspaceFolder}"],
+      "outFiles": ["${workspaceFolder}/out/**/*.cjs"],
+      "preLaunchTask": "npm: build"
+    }
+  ]
+}
diff --git a/.vscode/tasks.json b/.vscode/tasks.json
new file mode 100644
index 0000000..98c3d8b
--- /dev/null
+++ b/.vscode/tasks.json
@@ -0,0 +1,13 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "type": "npm",
+      "script": "build",
+      "group": "build",
+      "problemMatcher": ["$esbuild"],
+      "label": "npm: build",
+      "detail": "Bundle the extension with esbuild"
+    }
+  ]
+}
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..2939936
--- /dev/null
+++ b/README.md
@@ -0,0 +1,32 @@
+# 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.
diff --git a/docs/superpowers/plans/2026-06-09-poc-cline-sdk-extension.md b/docs/superpowers/plans/2026-06-09-poc-cline-sdk-extension.md
new file mode 100644
index 0000000..7a4924f
--- /dev/null
+++ b/docs/superpowers/plans/2026-06-09-poc-cline-sdk-extension.md
@@ -0,0 +1,468 @@
+# POC: Runnable VS Code Extension on `@cline/sdk` — Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Scaffold a standalone, non-shippable VS Code extension that builds, launches in the Extension Development Host on F5, and runs one command that drives `@cline/sdk` and shows a real result — validating Approach A (standalone extension on the Cline SDK, no fork).
+
+**Architecture:** A CommonJS VS Code extension bundled with esbuild (`vscode` and `@cline/sdk` both kept external). `@cline/sdk` is ESM-only (Node ≥22) and uses `createRequire(import.meta.url)`, so it **cannot** be bundled into a CJS extension — instead it is shipped in `node_modules` and loaded at runtime via dynamic `import('@cline/sdk')`. The SDK-driving logic lives in a vscode-free module (`src/cline.ts`) so it is unit-testable in Node; the vscode command wiring lives in `src/extension.ts`. The command calls the SDK's pure `getCoreBuiltinToolCatalog()` + `CORE_BUILD_VERSION` (no API keys, no agent run) and renders the result.
+
+**Tech Stack:** TypeScript, VS Code Extension API (`engines.vscode`), esbuild (bundler), vitest (unit test), `@cline/sdk@0.0.46`.
+
+**De-risking already done (empirical, see session 0002 transcript):**
+- `@cline/sdk@0.0.46` loads in Node 24; `CORE_BUILD_VERSION === "0.0.46"`; `getCoreBuiltinToolCatalog()` returns 9 entries with shape `{id, description, headlessToolNames, defaultEnabled}` (e.g. `read_files`, `search_codebase`, `run_commands`, `editor`, `fetch_web_content`).
+- Bundling the SDK **into** CJS fails (`import.meta.url` undefined → `createRequire` throws). Keeping it external + dynamic `import()` from a CJS bundle works and yields a ~2KB extension bundle.
+
+---
+
+## File Structure
+
+| File | Responsibility |
+| --- | --- |
+| `package.json` | Extension manifest: `main`, `engines.vscode`, `contributes.commands`, `activationEvents`, scripts, deps. |
+| `tsconfig.json` | TypeScript config (typecheck only; esbuild does the emit). |
+| `esbuild.mjs` | Bundle `src/extension.ts` → `out/extension.cjs`, externalize `vscode` + `@cline/sdk`. |
+| `src/cline.ts` | vscode-free SDK driver: `fetchSdkSummary()` dynamic-imports `@cline/sdk`, returns `{version, tools}`. Unit-testable. |
+| `src/extension.ts` | `activate`/`deactivate`; registers the `cowriting.showClineSdkInfo` command; renders the summary via notification + output channel. |
+| `test/cline.test.ts` | vitest unit test asserting `fetchSdkSummary()` returns a semver version and a non-empty tool list including `read_files`. |
+| `.vscode/launch.json` | F5 → "Run Extension" launches the Extension Development Host with this extension. |
+| `.vscode/tasks.json` | The `npm: build` task the launch config depends on. |
+| `.gitignore` | Ignore `node_modules/`, `out/`. |
+| `vitest.config.ts` | vitest node environment config. |
+| `README.md` | What the POC is + how to run it (F5). |
+
+---
+
+## Task 1: Project manifest and tooling config
+
+**Files:**
+- Create: `package.json`
+- Create: `tsconfig.json`
+- Create: `.gitignore`
+- Create: `vitest.config.ts`
+
+- [ ] **Step 1: Write `package.json`**
+
+```json
+{
+  "name": "vscode-cowriting-plugin",
+  "displayName": "Cowriting (Cline SDK POC)",
+  "description": "Non-shippable POC: a standalone VS Code extension that drives @cline/sdk.",
+  "version": "0.0.1",
+  "private": true,
+  "license": "Apache-2.0",
+  "publisher": "benstull",
+  "engines": {
+    "vscode": "^1.90.0",
+    "node": ">=22"
+  },
+  "categories": ["Other"],
+  "main": "./out/extension.cjs",
+  "activationEvents": [],
+  "contributes": {
+    "commands": [
+      {
+        "command": "cowriting.showClineSdkInfo",
+        "title": "Cowriting: Show Cline SDK Info",
+        "category": "Cowriting"
+      }
+    ]
+  },
+  "scripts": {
+    "build": "node esbuild.mjs",
+    "watch": "node esbuild.mjs --watch",
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run",
+    "vscode:prepublish": "node esbuild.mjs"
+  },
+  "dependencies": {
+    "@cline/sdk": "0.0.46"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "@types/vscode": "^1.90.0",
+    "esbuild": "^0.23.0",
+    "typescript": "^5.5.0",
+    "vitest": "^2.0.0"
+  }
+}
+```
+
+Note: `contributes.commands` declares the command without a `when`, so it appears in the Command Palette as soon as the extension activates. `activationEvents` is empty because declaring a command auto-generates `onCommand:` activation in VS Code ≥1.74.
+
+- [ ] **Step 2: Write `tsconfig.json`**
+
+```json
+{
+  "compilerOptions": {
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "target": "ES2022",
+    "lib": ["ES2022"],
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "resolveJsonModule": true,
+    "noEmit": true,
+    "types": ["node"]
+  },
+  "include": ["src", "test", "esbuild.mjs"]
+}
+```
+
+- [ ] **Step 3: Write `.gitignore`**
+
+```
+node_modules/
+out/
+*.vsix
+```
+
+- [ ] **Step 4: Write `vitest.config.ts`**
+
+```ts
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    environment: "node",
+    include: ["test/**/*.test.ts"],
+  },
+});
+```
+
+- [ ] **Step 5: Install dependencies**
+
+Run: `npm install`
+Expected: `node_modules/` populated, `@cline/sdk` present, no error exit.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add package.json tsconfig.json .gitignore vitest.config.ts package-lock.json
+git commit -m "POC scaffold: extension manifest + tooling config (Feature #2)"
+```
+
+---
+
+## Task 2: SDK driver module (TDD)
+
+**Files:**
+- Create: `src/cline.ts`
+- Test: `test/cline.test.ts`
+
+- [ ] **Step 1: Write the failing test**
+
+`test/cline.test.ts`:
+
+```ts
+import { describe, it, expect } from "vitest";
+import { fetchSdkSummary } from "../src/cline";
+
+describe("fetchSdkSummary", () => {
+  it("loads @cline/sdk and returns its version and builtin tool catalog", async () => {
+    const summary = await fetchSdkSummary();
+    expect(summary.version).toMatch(/^\d+\.\d+\.\d+/);
+    expect(summary.tools.length).toBeGreaterThan(0);
+    expect(summary.tools.map((t) => t.id)).toContain("read_files");
+    for (const tool of summary.tools) {
+      expect(typeof tool.id).toBe("string");
+      expect(typeof tool.description).toBe("string");
+    }
+  });
+});
+```
+
+- [ ] **Step 2: Run test to verify it fails**
+
+Run: `npm test`
+Expected: FAIL — cannot resolve `../src/cline` (module not created yet).
+
+- [ ] **Step 3: Write minimal implementation**
+
+`src/cline.ts`:
+
+```ts
+/**
+ * vscode-free driver for @cline/sdk.
+ *
+ * @cline/sdk is ESM-only (Node >=22) and uses createRequire(import.meta.url),
+ * so it must NOT be bundled into the CJS extension. We load it at runtime via
+ * dynamic import(); the bundler keeps it external (see esbuild.mjs).
+ */
+
+export interface ClineTool {
+  id: string;
+  description: string;
+}
+
+export interface SdkSummary {
+  version: string;
+  tools: ClineTool[];
+}
+
+/**
+ * Drive @cline/sdk with pure, key-free calls and return a renderable summary:
+ * the SDK build version and the agent's builtin tool catalog. Proves the SDK
+ * is linked and callable from the extension host.
+ */
+export async function fetchSdkSummary(): Promise<SdkSummary> {
+  const sdk = await import("@cline/sdk");
+  const catalog = sdk.getCoreBuiltinToolCatalog();
+  return {
+    version: sdk.CORE_BUILD_VERSION,
+    tools: catalog.map((entry) => ({
+      id: entry.id,
+      description: entry.description,
+    })),
+  };
+}
+```
+
+- [ ] **Step 4: Run test to verify it passes**
+
+Run: `npm test`
+Expected: PASS — version matches semver, tools include `read_files`.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/cline.ts test/cline.test.ts
+git commit -m "POC: vscode-free @cline/sdk driver with unit test (Feature #2)"
+```
+
+---
+
+## Task 3: Extension entry point and command wiring
+
+**Files:**
+- Create: `src/extension.ts`
+
+- [ ] **Step 1: Write `src/extension.ts`**
+
+```ts
+import * as vscode from "vscode";
+import { fetchSdkSummary } from "./cline";
+
+const CHANNEL_NAME = "Cowriting (Cline SDK)";
+
+export function activate(context: vscode.ExtensionContext): void {
+  const output = vscode.window.createOutputChannel(CHANNEL_NAME);
+  context.subscriptions.push(output);
+
+  const command = vscode.commands.registerCommand(
+    "cowriting.showClineSdkInfo",
+    async () => {
+      try {
+        const summary = await fetchSdkSummary();
+        output.clear();
+        output.appendLine(`@cline/sdk version: ${summary.version}`);
+        output.appendLine(`Builtin tools (${summary.tools.length}):`);
+        for (const tool of summary.tools) {
+          output.appendLine(`  • ${tool.id} — ${tool.description}`);
+        }
+        output.show(true);
+        await vscode.window.showInformationMessage(
+          `Cline SDK ${summary.version} loaded — ${summary.tools.length} builtin tools. See the "${CHANNEL_NAME}" output channel.`
+        );
+      } catch (err) {
+        const message = err instanceof Error ? err.message : String(err);
+        output.appendLine(`Failed to drive @cline/sdk: ${message}`);
+        output.show(true);
+        await vscode.window.showErrorMessage(
+          `Cowriting: failed to load @cline/sdk — ${message}`
+        );
+      }
+    }
+  );
+  context.subscriptions.push(command);
+}
+
+export function deactivate(): void {
+  // Nothing to clean up beyond the disposables registered on the context.
+}
+```
+
+- [ ] **Step 2: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS — no type errors (requires `@types/vscode` and `@types/node`).
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add src/extension.ts
+git commit -m "POC: extension activate + showClineSdkInfo command (Feature #2)"
+```
+
+---
+
+## Task 4: esbuild bundle
+
+**Files:**
+- Create: `esbuild.mjs`
+
+- [ ] **Step 1: Write `esbuild.mjs`**
+
+```js
+import { build, context } from "esbuild";
+
+const watch = process.argv.includes("--watch");
+
+/** @type {import('esbuild').BuildOptions} */
+const options = {
+  entryPoints: ["src/extension.ts"],
+  outfile: "out/extension.cjs",
+  bundle: true,
+  platform: "node",
+  format: "cjs",
+  target: "node20",
+  sourcemap: true,
+  // vscode is provided by the host; @cline/sdk is ESM-only and is loaded at
+  // runtime via dynamic import() from node_modules, so keep both external.
+  external: ["vscode", "@cline/sdk"],
+  logLevel: "info",
+};
+
+if (watch) {
+  const ctx = await context(options);
+  await ctx.watch();
+  console.log("esbuild: watching…");
+} else {
+  await build(options);
+  console.log("esbuild: build complete → out/extension.cjs");
+}
+```
+
+- [ ] **Step 2: Build**
+
+Run: `npm run build`
+Expected: `out/extension.cjs` created; log "build complete". Bundle is small (~few KB) because the SDK is external.
+
+- [ ] **Step 3: Verify the bundle keeps the SDK external**
+
+Run: `node -e "const s=require('fs').readFileSync('out/extension.cjs','utf8'); console.log('has dynamic import of sdk:', s.includes('@cline/sdk')); console.log('bytes:', s.length)"`
+Expected: `has dynamic import of sdk: true`; byte count in the low thousands (SDK not inlined).
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add esbuild.mjs
+git commit -m "POC: esbuild bundle (vscode + @cline/sdk external) (Feature #2)"
+```
+
+---
+
+## Task 5: F5 launch configuration
+
+**Files:**
+- Create: `.vscode/launch.json`
+- Create: `.vscode/tasks.json`
+
+- [ ] **Step 1: Write `.vscode/tasks.json`**
+
+```json
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "type": "npm",
+      "script": "build",
+      "group": "build",
+      "problemMatcher": ["$esbuild"],
+      "label": "npm: build",
+      "detail": "Bundle the extension with esbuild"
+    }
+  ]
+}
+```
+
+- [ ] **Step 2: Write `.vscode/launch.json`**
+
+```json
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Run Extension",
+      "type": "extensionHost",
+      "request": "launch",
+      "args": ["--extensionDevelopmentPath=${workspaceFolder}"],
+      "outFiles": ["${workspaceFolder}/out/**/*.cjs"],
+      "preLaunchTask": "npm: build"
+    }
+  ]
+}
+```
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add .vscode/launch.json .vscode/tasks.json
+git commit -m "POC: F5 Run Extension launch config (Feature #2)"
+```
+
+---
+
+## Task 6: README and verification
+
+**Files:**
+- Create: `README.md`
+
+- [ ] **Step 1: Write `README.md`**
+
+```markdown
+# 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.
+```
+
+- [ ] **Step 2: Full verification sweep**
+
+Run: `npm install && npm run typecheck && npm test && npm run build`
+Expected: install OK; typecheck OK; 1 test passes; build writes `out/extension.cjs`.
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add README.md
+git commit -m "POC: README with run/dev instructions (Feature #2)"
+```
+
+---
+
+## Manual / operator verification (cannot be automated in-session)
+
+- [ ] Press **F5** in VS Code → Extension Development Host opens with no activation error.
+- [ ] Run **"Cowriting: Show Cline SDK Info"** → notification shows `Cline SDK 0.0.46 loaded — 9 builtin tools`, and the output channel lists the 9 tool IDs with descriptions.
+
+This is the POC's acceptance: repo builds, F5 launches the host with the
+extension active, and one command drives `@cline/sdk` and shows a real result.