Process management improvements (#881)

This PR improves process lifecycle handling and resilience across several areas:

- **Reclaim stale shared-memory entries instead of exiting** (`zenserver.cpp`): When a zenserver instance fails to attach as a sponsor to an existing process (e.g. because the PID was reused by an unrelated process), the server now clears the stale shared-memory entry and proceeds with normal startup instead of calling `std::exit(1)`.

- **Wait for child process exit in `Kill()` and `Terminate()` on Unix** (`process.cpp`): After sending `SIGTERM` in `Kill()`, the code now waits up to 5s for graceful shutdown (escalating to `SIGKILL` on timeout), matching the Windows behavior. `Terminate()` also waits after `SIGKILL` so the child is properly reaped and doesn't linger as a zombie clogging up the process table.

- **Fix sysctl buffer race in macOS `FindProcess`** (`process.cpp`): The macOS process enumeration now retries the `sysctl` call (up to 3 attempts with 25% buffer padding) to handle the race where the process list changes between the sizing call and the data-fetching call. Also flattens the nesting and fixes the guard/free scoping.

- **Terminate stale processes before integration tests** (`zenserver-test.cpp`, `test.lua`): The integration test runner now accepts a `--kill-stale-processes` flag (passed automatically by `test.lua`) that scans for and terminates any leftover `zenserver`, `zenserver-test`, and `zentest-appstub` processes from previous test runs, logging the executable name and PID of each. This addresses flaky test failures caused by stale processes from prior runs holding ports or other resources.

1 files changed, 40 insertions, 1 deletions

diff --git a/src/zenserver-test/zenserver-test.cpp b/src/zenserver-test/zenserver-test.cpp
index fff77957d..cf7ffe4e4 100644
--- a/src/zenserver-test/zenserver-test.cpp
+++ b/src/zenserver-test/zenserver-test.cpp
@@ -99,7 +99,8 @@ main(int argc, char** argv)
 	// somehow in the future
 
 	std::string ServerClass;
-	bool		Verbose = false;
+	bool		Verbose	  = false;
+	bool		KillStale = false;
 
 	for (int i = 1; i < argc; ++i)
 	{
@@ -119,6 +120,44 @@ main(int argc, char** argv)
 		{
 			Verbose = true;
 		}
+		else if (argv[i] == "--kill-stale-processes"sv)
+		{
+			KillStale = true;
+		}
+	}
+
+	// Since GHA runners can leave processes behind from a previous test run, we need
+	// to be able to clean up any stale server processes before starting the tests to
+	// avoid interference
+
+	if (KillStale)
+	{
+		ZEN_INFO("Killing any stale processes from previous test runs...");
+
+		auto KillStaleProcesses = [](const std::filesystem::path& Executable) {
+			ZEN_INFO("  Looking for stale '{}' processes...", Executable.filename());
+
+			for (;;)
+			{
+				ProcessHandle	StaleProcess;
+				std::error_code Ec = FindProcess(Executable, StaleProcess, /*IncludeSelf*/ false);
+
+				if (Ec || !StaleProcess.IsValid())
+				{
+					break;
+				}
+
+				ZEN_WARN("====> Found stale '{}' process (pid {}) from a previous test run - terminating it",
+						 Executable.filename(),
+						 StaleProcess.Pid());
+
+				StaleProcess.Terminate(0);
+			}
+		};
+
+		KillStaleProcesses(ProgramBaseDir / "zenserver" ZEN_EXE_SUFFIX_LITERAL);
+		KillStaleProcesses(ProgramBaseDir / "zenserver-test" ZEN_EXE_SUFFIX_LITERAL);
+		KillStaleProcesses(ProgramBaseDir / "zentest-appstub" ZEN_EXE_SUFFIX_LITERAL);
 	}
 
 	zen::tests::TestEnv.InitializeForTest(ProgramBaseDir, TestBaseDir, ServerClass);