Keep Copilot installer contracts complete in the runtime partition

Include the server lifecycle shim with its package tests. Retain extended native-session coverage in the following regression partition so each review stays below 100 files.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/scripts/install-copilot-assets.mjs

@@ -0,0 +1,18 @@
+import { access } from "node:fs/promises";
+import { fileURLToPath } from "node:url";
+
+const installer = new URL("../dist/install-copilot-assets.mjs", import.meta.url);
+try {
+  await access(fileURLToPath(installer));
+} catch (error) {
+  if (error.code !== "ENOENT") throw error;
+  // Dependencies install before compilation in a source workspace. Published
+  // server packages omit src and cannot take this bootstrap exception.
+  await access(fileURLToPath(new URL("../src/services/copilot-connection-probe.ts", import.meta.url)));
+  await access(fileURLToPath(new URL("../../pnpm-workspace.yaml", import.meta.url)));
+  process.stdout.write("Copilot runtime assets: source-workspace-pending-build\n");
+  process.exit(0);
+}
+const { installCopilotAssets } = await import(installer.href);
+const result = await installCopilotAssets();
+process.stdout.write(`Copilot runtime assets: ${result.status} (${result.target})\n`);