POC: extension entry + esbuild bundle (Feature #2)

activate() registers showClineSdkInfo, which renders the SDK summary to a
notification and output channel. esbuild bundles to CJS, keeping vscode and
@cline/sdk external (the ESM SDK loads via runtime dynamic import).

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

src/extension.ts

@@ -0,0 +1,40 @@
+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.
+}