fix: handle npm git dep installation for GitHub installs

npm v11's git dep preparation runs `prepare` before node_modules exist
in the temp clone directory. This causes TypeScript compilation to fail.

Changes:
- build.js: skip build gracefully when node_modules absent, use
  node directly instead of pnpm for npm compatibility
- package.json: add `prepack` hook for pack-phase build, make
  postinstall non-fatal (|| true) to handle stale CWD after temp
  dir cleanup

Install from GitHub with:
  npm pack github:user/repo#branch
  npm install -g ./fission-ai-openspec-1.2.0.tgz

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pformoso-deus-ai

build.js

@@ -4,6 +4,14 @@ import { execFileSync } from 'child_process';
 import { existsSync, rmSync } from 'fs';
 import { createRequire } from 'module';
 
+// When npm installs from a git dep (github:user/repo#branch), it runs
+// `prepare` before node_modules exist. Skip gracefully and let `prepack`
+// handle the build during the pack phase where deps are available.
+if (!existsSync('node_modules')) {
+  console.log('⏭️  Skipping build (node_modules not yet available)');
+  process.exit(0);
+}
+
 const require = createRequire(import.meta.url);
 
 const runTsc = (args = []) => {

package.json

@@ -48,9 +48,10 @@
     "test:ui": "vitest --ui",
     "test:coverage": "vitest --coverage",
     "test:postinstall": "node scripts/postinstall.js",
-    "prepare": "pnpm run build",
+    "prepare": "node build.js",
+    "prepack": "node build.js",
     "prepublishOnly": "pnpm run build",
-    "postinstall": "node scripts/postinstall.js",
+    "postinstall": "node scripts/postinstall.js || true",
     "check:pack-version": "node scripts/pack-version-check.mjs",
     "release": "pnpm run release:ci",
     "release:ci": "pnpm run check:pack-version && pnpm exec changeset publish",