Address Copilot review: anchor regex, normalise paths, don't stack on MIT files

- Drop the /m flag from the copyright regex so the banner must be the first line
  (post-shebang), not merely present somewhere in the file head.
- Normalise incoming paths to repo-relative POSIX before matching. lint-staged
  passes absolute (and on Windows, backslashed) paths, which never matched the
  include-dir prefixes — so the per-file invocation was silently a no-op. Now it
  actually enforces headers on staged files.
- Three CE-authored files (lib/stack-usage-transformer.ts,
  test/stack-usage-transformer-test.ts, test/library-tests.ts) carry an MIT
  header rather than the repo-standard BSD-2; the backfill had stacked a BSD-2
  banner on top, leaving two conflicting licenses. Revert those to their original
  single MIT header and exempt them from the check. Relicensing them to BSD-2 is
  a separate maintainer decision.

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

etc/scripts/check-license-headers.js

@@ -11,6 +11,7 @@
 
 import {execSync} from 'node:child_process';
 import fs from 'node:fs';
+import path from 'node:path';
 
 // Directories/globs whose source files must carry the banner.
 const INCLUDE_DIRS = ['lib', 'static', 'shared', 'types', 'test', 'cypress'];
@@ -27,16 +28,30 @@ const EXCLUDE_PATTERNS = [
     /^static\/ansi-to-html\.ts$/, // MIT, Rob Burns
     /^lib\/node-graceful\.ts$/, // MIT, node-graceful
     /^shared\/rison\.ts$/, // Nanonid/rison port
+    // CE-authored files that pre-date this check and carry an MIT header rather than
+    // the repo-standard BSD-2. Exempt for now; relicensing them to BSD-2 is a separate
+    // call for a maintainer.
+    /^lib\/stack-usage-transformer\.ts$/,
+    /^test\/stack-usage-transformer-test\.ts$/,
+    /^test\/library-tests\.ts$/,
 ];
 
 // A file "has an appropriate banner" if, ignoring an optional shebang, it opens
 // with a `// Copyright (c) ...` line and contains the BSD-2-Clause disclaimer.
 // The year and copyright holder are intentionally not constrained: the tree has
 // many holders (Compiler Explorer Authors, Arm Ltd, Microsoft, individuals, ...).
-const COPYRIGHT_RE = /^\/\/ Copyright \([cC]\) .+/m;
+// No /m flag: the copyright line must be the very first line (post-shebang), not
+// merely present somewhere in the head.
+const COPYRIGHT_RE = /^\/\/ Copyright \([cC]\) .+/;
 // A couple of older files quote AS IS with single quotes; accept either.
 const DISCLAIMER_RE = /THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ["']AS IS["']/;
 
+// Normalise to a repo-relative POSIX path so matching works whether we're handed
+// tracked paths from `git ls-files` or absolute/backslashed paths from lint-staged.
+function toRepoRelative(file) {
+    return path.relative(process.cwd(), path.resolve(file)).split(path.sep).join('/');
+}
+
 function isIncluded(file) {
     if (!INCLUDE_EXTENSIONS.some(ext => file.endsWith(ext))) return false;
     if (EXCLUDE_PATTERNS.some(re => re.test(file))) return false;
@@ -67,7 +82,7 @@ function hasBanner(file) {
 }
 
 const args = process.argv.slice(2);
-const candidates = (args.length > 0 ? args : listTrackedFiles()).filter(isIncluded);
+const candidates = (args.length > 0 ? args : listTrackedFiles()).map(toRepoRelative).filter(isIncluded);
 const missing = candidates.filter(file => fs.existsSync(file) && !hasBanner(file));
 
 if (missing.length > 0) {

lib/stack-usage-transformer.ts

@@ -1,27 +1,3 @@
-// Copyright (c) 2023, Compiler Explorer Authors
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are met:
-//
-//     * Redistributions of source code must retain the above copyright notice,
-//       this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above copyright
-//       notice, this list of conditions and the following disclaimer in the
-//       documentation and/or other materials provided with the distribution.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
-// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-// POSSIBILITY OF SUCH DAMAGE.
-
 // Copyright (c) 2023, Compiler Explorer Authors
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy

test/library-tests.ts

@@ -1,27 +1,3 @@
-// Copyright (c) 2024, Compiler Explorer Authors
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are met:
-//
-//     * Redistributions of source code must retain the above copyright notice,
-//       this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above copyright
-//       notice, this list of conditions and the following disclaimer in the
-//       documentation and/or other materials provided with the distribution.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
-// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-// POSSIBILITY OF SUCH DAMAGE.
-
 // Copyright (c) 2024, Compiler Explorer Authors
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy

test/stack-usage-transformer-test.ts

@@ -1,27 +1,3 @@
-// Copyright (c) 2023, Compiler Explorer Authors
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are met:
-//
-//     * Redistributions of source code must retain the above copyright notice,
-//       this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above copyright
-//       notice, this list of conditions and the following disclaimer in the
-//       documentation and/or other materials provided with the distribution.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
-// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-// POSSIBILITY OF SUCH DAMAGE.
-
 // Copyright (c) 2023, Compiler Explorer Authors
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy