test: add coverage flush helper

apps/macos/Tests/ClawdisIPCTests/CoverageDumpTests.swift

@@ -0,0 +1,18 @@
+import Darwin
+import Foundation
+import Testing
+
+@Suite(.serialized)
+struct CoverageDumpTests {
+    @Test func periodicallyFlushCoverage() async {
+        guard ProcessInfo.processInfo.environment["LLVM_PROFILE_FILE"] != nil else { return }
+        let deadline = Date().addingTimeInterval(4)
+        while Date() < deadline {
+            _ = llvmProfileWriteFile()
+            try? await Task.sleep(nanoseconds: 250_000_000)
+        }
+    }
+}
+
+@_silgen_name("__llvm_profile_write_file")
+private func llvmProfileWriteFile() -> Int32