zencore: CreateProc stdin pipes + BuildArgV quote stripping (#983)

Two related improvements to `CreateProc`:

### 1. Stdin pipe support
- Adds `StdinPipeHandles` + `CreateStdinPipe` alongside the existing `StdoutPipeHandles`, letting callers feed data into a child process's stdin.
- Platform-agnostic RAII (Windows `HANDLE` pair / POSIX `pipe()` fd pair) with the same semantics as the stdout pipe: the inherited end goes to the child, the non-inherited end stays with the parent, destructor closes both.
- `CreateProcOptions` gains a `StdinPipe*` field.
- On Windows, `CreateProcNormal` is reworked so stdin/stdout redirection handles all combinations (stdin + stdout, each alone, neither) uniformly. POSIX already supported arbitrary fd redirection and just needed to honor the new option.
- `zentest-appstub` gains a `-stdin_echo` mode that reads stdin to EOF and echoes it back (switching to binary mode on Windows so CRLF translation doesn't mangle bytes).
- `zenserver-test` gets a `server.process` / `stdin_pipe.*` test group that exercises launching a child with a stdin pipe, writing, closing the write end, and reading back the echoed data.

### 2. Shell-style quote stripping in `BuildArgV`
- Callers that build a single command-line string for `CreateProc` commonly wrap spacey paths in double quotes (e.g. `--tracefile="$path"`). The old `BuildArgV` only used quotes to suppress space-splitting and left the characters in the resulting argv element, so the spawned process saw literal `--tracefile="..."` and the value parser failed to open the quoted path.
- `BuildArgV` now compacts in place, dropping quote chars as it goes, matching shell semantics for paired double quotes.

1 files changed, 136 insertions, 0 deletions

diff --git a/src/zenserver-test/process-tests.cpp b/src/zenserver-test/process-tests.cpp
index 3f6476810..16af1879a 100644
--- a/src/zenserver-test/process-tests.cpp
+++ b/src/zenserver-test/process-tests.cpp
@@ -13,6 +13,7 @@
 #	if ZEN_PLATFORM_WINDOWS
 #		include <zencore/windows.h>
 #	else
+#		include <cerrno>
 #		include <unistd.h>
 #	endif
 
@@ -51,6 +52,45 @@ ReadAllFromPipe(StdoutPipeHandles& Pipe)
 	return Result;
 }
 
+// Write all of @p Data to the write end of a StdinPipeHandles. Returns true on success.
+static bool
+WriteAllToPipe(StdinPipeHandles& Pipe, std::string_view Data)
+{
+#	if ZEN_PLATFORM_WINDOWS
+	const char* Ptr		  = Data.data();
+	size_t		Remaining = Data.size();
+	while (Remaining > 0)
+	{
+		DWORD BytesWritten = 0;
+		if (!::WriteFile(Pipe.WriteHandle, Ptr, static_cast<DWORD>(Remaining), &BytesWritten, nullptr) || BytesWritten == 0)
+		{
+			return false;
+		}
+		Ptr += BytesWritten;
+		Remaining -= BytesWritten;
+	}
+	return true;
+#	else
+	const char* Ptr		  = Data.data();
+	size_t		Remaining = Data.size();
+	while (Remaining > 0)
+	{
+		ssize_t BytesWritten = write(Pipe.WriteFd, Ptr, Remaining);
+		if (BytesWritten <= 0)
+		{
+			if (BytesWritten < 0 && errno == EINTR)
+			{
+				continue;
+			}
+			return false;
+		}
+		Ptr += BytesWritten;
+		Remaining -= static_cast<size_t>(BytesWritten);
+	}
+	return true;
+#	endif
+}
+
 TEST_SUITE_BEGIN("server.process");
 
 //////////////////////////////////////////////////////////////////////////
@@ -276,6 +316,102 @@ TEST_CASE("pipe.separate_stderr")
 
 //////////////////////////////////////////////////////////////////////////
 
+TEST_CASE("stdin_pipe.echo_round_trip")
+{
+	StdinPipeHandles  StdinPipe;
+	StdoutPipeHandles StdoutPipe;
+	REQUIRE(CreateStdinPipe(StdinPipe));
+	REQUIRE(CreateStdoutPipe(StdoutPipe));
+
+	const std::string	  Input		  = "hello-from-stdin\nsecond-line\n";
+	std::filesystem::path AppStub	  = GetAppStubPath();
+	std::string			  CommandLine = "zentest-appstub -stdin_echo";
+
+	CreateProcOptions Options;
+	Options.StdinPipe  = &StdinPipe;
+	Options.StdoutPipe = &StdoutPipe;
+
+	ProcessHandle Process(CreateProc(AppStub, CommandLine, Options));
+
+	// Close the read end (child side) so that when we finish writing and close the write end,
+	// the child sees EOF. Also close the stdout write end so our reads see EOF after the child exits.
+	StdinPipe.CloseReadEnd();
+	StdoutPipe.CloseWriteEnd();
+
+	REQUIRE(WriteAllToPipe(StdinPipe, Input));
+	StdinPipe.CloseWriteEnd();	// signals EOF to the child
+
+	std::string Output = ReadAllFromPipe(StdoutPipe);
+
+	Process.Wait();
+
+	CHECK(Output.find(Input) != std::string::npos);
+	CHECK_EQ(Process.GetExitCode(), 0);
+}
+
+TEST_CASE("stdin_pipe.raii_cleanup")
+{
+	for (int i = 0; i < 100; ++i)
+	{
+		StdinPipeHandles Pipe;
+		REQUIRE(CreateStdinPipe(Pipe));
+	}
+}
+
+TEST_CASE("stdin_pipe.move_semantics")
+{
+	StdinPipeHandles Original;
+	REQUIRE(CreateStdinPipe(Original));
+
+	StdinPipeHandles Moved(std::move(Original));
+
+#	if ZEN_PLATFORM_WINDOWS
+	CHECK(Moved.ReadHandle != nullptr);
+	CHECK(Moved.WriteHandle != nullptr);
+	CHECK(Original.ReadHandle == nullptr);
+	CHECK(Original.WriteHandle == nullptr);
+#	else
+	CHECK(Moved.ReadFd >= 0);
+	CHECK(Moved.WriteFd >= 0);
+	CHECK(Original.ReadFd == -1);
+	CHECK(Original.WriteFd == -1);
+#	endif
+
+	StdinPipeHandles Assigned;
+	Assigned = std::move(Moved);
+
+#	if ZEN_PLATFORM_WINDOWS
+	CHECK(Assigned.ReadHandle != nullptr);
+	CHECK(Assigned.WriteHandle != nullptr);
+	CHECK(Moved.ReadHandle == nullptr);
+	CHECK(Moved.WriteHandle == nullptr);
+#	else
+	CHECK(Assigned.ReadFd >= 0);
+	CHECK(Assigned.WriteFd >= 0);
+	CHECK(Moved.ReadFd == -1);
+	CHECK(Moved.WriteFd == -1);
+#	endif
+}
+
+TEST_CASE("stdin_pipe.close_is_idempotent")
+{
+	StdinPipeHandles Pipe;
+	REQUIRE(CreateStdinPipe(Pipe));
+
+	Pipe.Close();
+	Pipe.Close();
+
+#	if ZEN_PLATFORM_WINDOWS
+	CHECK(Pipe.ReadHandle == nullptr);
+	CHECK(Pipe.WriteHandle == nullptr);
+#	else
+	CHECK(Pipe.ReadFd == -1);
+	CHECK(Pipe.WriteFd == -1);
+#	endif
+}
+
+//////////////////////////////////////////////////////////////////////////
+
 TEST_SUITE_END();
 
 }  // namespace zen::tests