[ISSUE-30478] Release cache dir lock acquired by a command on sigint or sigterm (#52194)

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -622,6 +622,7 @@ abstract class FlutterCommand extends Command<void> {
 
   void _registerSignalHandlers(String commandPath, DateTime startTime) {
     final SignalHandler handler = (io.ProcessSignal s) {
+      Cache.releaseLockEarly();
       _sendPostUsage(
         commandPath,
         const FlutterCommandResult(ExitStatus.killed),

packages/flutter_tools/test/general.shard/runner/flutter_command_test.dart

@@ -287,6 +287,43 @@ void main() {
         SystemClock: () => clock,
         Usage: () => usage,
       });
+
+      testUsingContext('command release lock on kill signal', () async {
+        mockTimes = <int>[1000, 2000];
+        final Completer<void> completer = Completer<void>();
+        setExitFunctionForTests((int exitCode) {
+          expect(exitCode, 0);
+          restoreExitFunction();
+          completer.complete();
+        });
+        final Completer<void> checkLockCompleter = Completer<void>();
+        final DummyFlutterCommand flutterCommand =
+            DummyFlutterCommand(commandFunction: () async {
+          await Cache.lock();
+          checkLockCompleter.complete();
+          final Completer<void> c = Completer<void>();
+          await c.future;
+          return null; // unreachable
+        });
+
+        unawaited(flutterCommand.run());
+        await checkLockCompleter.future;
+
+        Cache.checkLockAcquired();
+
+        signalController.add(mockSignal);
+        await completer.future;
+
+        await Cache.lock();
+        Cache.releaseLockEarly();
+      }, overrides: <Type, Generator>{
+        ProcessInfo: () => mockProcessInfo,
+        Signals: () => FakeSignals(
+              subForSigTerm: signalUnderTest,
+              exitSignals: <ProcessSignal>[signalUnderTest],
+            ),
+        Usage: () => usage
+      });
     });
 
     testUsingCommandContext('report execution timing by default', () async {