fix(mac): resolve duplicate symbols blocking darwin/linux builds + add Mac tests. Remove duplicate launchProcessGuard from guard_unix.go (kept richer health_unix.go shell-loop version using pgrep -f). Remove duplicate applyDetachedStart from exec_stub.go (kept platform_unix.go impl that clears stdio). Add silent_stub.go for !windows so silentCombinedOutput/silentOutput/silentRun compile on Mac. All 4 targets now build: darwin/arm64, darwin/amd64, linux/amd64, linux/arm64. New tests: workerProcessRunning, applyDetachedStart stdio clearing, PersistenceKeyName, HostOSVersion, LaunchAgent plist content, silent stub exec wrappers.

agent/client/silent_stub.go

@@ -0,0 +1,28 @@
+//go:build !windows
+
+package client
+
+import "os/exec"
+
+// On non-Windows there are no console windows to hide; these are
+// plain exec wrappers that mirror the silent_windows.go signatures.
+
+func silentCmd(name string, arg ...string) *exec.Cmd {
+	return exec.Command(name, arg...)
+}
+
+func silentCombinedOutput(name string, arg ...string) ([]byte, error) {
+	return exec.Command(name, arg...).CombinedOutput()
+}
+
+func silentOutput(name string, arg ...string) ([]byte, error) {
+	return exec.Command(name, arg...).Output()
+}
+
+func silentRun(name string, arg ...string) error {
+	return exec.Command(name, arg...).Run()
+}
+
+func silentStart(cmd *exec.Cmd) error {
+	return cmd.Start()
+}