feat(deps): pre-commit type-check on staged TS files

Pre-commit now runs `tsc` against the staged ts/tsx files (and their
dep graph) in ~3s, catching type errors before they hit CI. Used to
skip type-check entirely on pre-commit because full-project tsc is
~22s — too slow for the commit hook.

Drops a 30-LOC shim in `scripts/tsc-staged.mjs` instead of the
`tsc-files` package: that lib's binary-resolution path
(`typescript/../.bin/tsc`) doesn't exist under pnpm's virtual-store
layout, so spawnSync returns `status: null` and the check silently
no-ops. Filed upstream-style: the package hasn't shipped in 3 years.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.lintstagedrc.json

@@ -1,4 +1,4 @@
 {
-  "*.{ts,tsx}": ["eslint --fix", "prettier --write"],
+  "*.{ts,tsx}": ["eslint --fix", "prettier --write", "node scripts/tsc-staged.mjs"],
   "*.{json,md,css}": ["prettier --write"]
 }

scripts/tsc-staged.mjs

@@ -0,0 +1,55 @@
+#!/usr/bin/env node
+/**
+ * Pre-commit type check for staged TS files.
+ *
+ * Writes a temp tsconfig that extends the project root and pins
+ * `files` to whatever lint-staged passed in. `tsc -p` then compiles
+ * the whole dep graph from those entrypoints — catches errors in
+ * the staged code AND in anything it imports — while still skipping
+ * the 22s full-project pass.
+ *
+ * Replaces `tsc-files` (npm), which silently fails under pnpm because
+ * its tsc-resolution path (typescript/../.bin/tsc) doesn't exist in
+ * pnpm's virtual store layout.
+ */
+
+import { spawnSync } from 'node:child_process';
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join, relative, resolve } from 'node:path';
+
+const cwd = process.cwd();
+const args = process.argv.slice(2);
+const files = args.filter((a) => /\.(ts|tsx)$/.test(a));
+
+if (files.length === 0) {
+  process.exit(0);
+}
+
+const tmpDir = mkdtempSync(join(tmpdir(), 'tsc-staged-'));
+const tmpConfig = join(tmpDir, 'tsconfig.json');
+
+const relFiles = files.map((f) => relative(tmpDir, resolve(cwd, f)));
+
+writeFileSync(
+  tmpConfig,
+  JSON.stringify(
+    {
+      extends: relative(tmpDir, join(cwd, 'tsconfig.json')),
+      compilerOptions: { noEmit: true, skipLibCheck: true },
+      files: relFiles,
+      include: [],
+    },
+    null,
+    2,
+  ),
+);
+
+const tsc = spawnSync('pnpm', ['exec', 'tsc', '-p', tmpConfig, '--pretty'], {
+  cwd,
+  stdio: 'inherit',
+});
+
+rmSync(tmpDir, { recursive: true, force: true });
+
+process.exit(tsc.status ?? 1);