Proposed change for cypherstack/flutter_libmwc (hook/build.dart).
VERIFIED once on NixOS (trek, 2026-11-01): patch applied to the pub-cache copy of flutter_libmwc d8c5d54, empty .cargo/config.toml,
MWC hook outputs deleted, `make build-linux` passed (about 6 min, no "protoc failed"). Control without patch and config failed with
"protoc failed: Could not start dynamically linked executable". Not tested on Ubuntu/macOS/Windows.

Problem: on NixOS the `protoc` binary bundled in prost-build 0.7 (pulled in by mwc-libp2p-core) cannot run,
and the PROTOC variable of the developer's shell never reaches cargo because hooks_runner filters the hook's
environment (Flutter 3.47.x). Today a developer needs a .cargo/config.toml with [env] PROTOC.

Idea: let the hook hand cargo a protoc found on PATH (PATH is on the allowlist). Falls back to prost's bundled
one when no protoc is installed, so nothing changes where it already works.

--- a/hook/build.dart
+++ b/hook/build.dart
@@
     final environment = <String, String>{
+      if (_findOnPath('protoc') case final protoc?) "PROTOC": protoc,
       if (code.targetOS == .iOS)
@@
+String? _findOnPath(String name) {
+  final sep = Platform.isWindows ? ';' : ':';
+  final exe = Platform.isWindows ? '$name.exe' : name;
+  for (final dir in (Platform.environment['PATH'] ?? '').split(sep)) {
+    if (dir.isEmpty) continue;
+    final f = File('$dir${Platform.pathSeparator}$exe');
+    if (f.existsSync()) return f.path;
+  }
+  return null;
+}

Longer term: move mwc-libp2p-core to prost-build >= 0.11, which expects protoc from PATH/PROTOC instead of
shipping a generic-Linux binary; then no hook change is needed.