test(macos): guard FileHandle read APIs

apps/macos/Tests/ClawdisIPCTests/FileHandleSafeReadTests.swift

@@ -0,0 +1,47 @@
+import Foundation
+import Testing
+@testable import Clawdis
+
+@Suite struct FileHandleSafeReadTests {
+    @Test func readToEndSafelyReturnsEmptyForClosedHandle() {
+        let pipe = Pipe()
+        let handle = pipe.fileHandleForReading
+        try? handle.close()
+
+        let data = handle.readToEndSafely()
+        #expect(data.isEmpty)
+    }
+
+    @Test func readSafelyUpToCountReturnsEmptyForClosedHandle() {
+        let pipe = Pipe()
+        let handle = pipe.fileHandleForReading
+        try? handle.close()
+
+        let data = handle.readSafely(upToCount: 16)
+        #expect(data.isEmpty)
+    }
+
+    @Test func readToEndSafelyReadsPipeContents() {
+        let pipe = Pipe()
+        let writeHandle = pipe.fileHandleForWriting
+        writeHandle.write(Data("hello".utf8))
+        try? writeHandle.close()
+
+        let data = pipe.fileHandleForReading.readToEndSafely()
+        #expect(String(data: data, encoding: .utf8) == "hello")
+    }
+
+    @Test func readSafelyUpToCountReadsIncrementally() {
+        let pipe = Pipe()
+        let writeHandle = pipe.fileHandleForWriting
+        writeHandle.write(Data("hello world".utf8))
+        try? writeHandle.close()
+
+        let readHandle = pipe.fileHandleForReading
+        let first = readHandle.readSafely(upToCount: 5)
+        let second = readHandle.readSafely(upToCount: 32)
+
+        #expect(String(data: first, encoding: .utf8) == "hello")
+        #expect(String(data: second, encoding: .utf8) == " world")
+    }
+}