feat(installer): add runtime manager core library

src/lib/runtime-manager.ts

@@ -0,0 +1,41 @@
+import path from 'node:path';
+
+const SEMVER_PATTERN = /^v?\d+\.\d+\.\d+(?:[-+][0-9A-Za-z.-]+)?$/;
+
+function ensureNonEmpty(value: string, field: string): string {
+  const normalized = value.trim();
+  if (!normalized) {
+    throw new Error(`${field} must be a non-empty string`);
+  }
+  return normalized;
+}
+
+export function normalizeVersion(version: string): string {
+  const normalized = ensureNonEmpty(version, 'version');
+  if (!SEMVER_PATTERN.test(normalized)) {
+    throw new Error(`version must be semver-compatible: ${version}`);
+  }
+  return normalized.startsWith('v') ? normalized.slice(1) : normalized;
+}
+
+export function resolveInstallHome(env: NodeJS.ProcessEnv): string {
+  const home = env.BB_INSTALL_HOME ?? env.HOME ?? env.USERPROFILE;
+  return ensureNonEmpty(home ?? '', 'install home');
+}
+
+export function getRuntimePaths(home: string, version: string) {
+  const installHome = ensureNonEmpty(home, 'home');
+  const normalizedVersion = normalizeVersion(version);
+  const beadboardHome = path.join(installHome, '.beadboard');
+  const runtimeBase = path.join(beadboardHome, 'runtime');
+
+  return {
+    installHome,
+    beadboardHome,
+    runtimeBase,
+    runtimeRoot: path.join(runtimeBase, normalizedVersion),
+    runtimeCurrentMetadata: path.join(runtimeBase, 'current.json'),
+    shimDir: path.join(beadboardHome, 'bin'),
+    shimNames: ['bb', 'beadboard'] as const,
+  };
+}