Fix vmexec PTY output truncation on Linux

vminitd/Package.swift

@@ -67,5 +67,9 @@ let package = Package(
                 .product(name: "VminitdCore", package: "containerization"),
             ]
         ),
+        .testTarget(
+            name: "vmexecTests",
+            dependencies: ["vmexec"]
+        ),
     ]
 )

vminitd/Sources/vmexec/Console.swift

@@ -14,6 +14,7 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
+import ContainerizationOS
 import FoundationEssentials
 import LCShim
 
@@ -55,6 +56,8 @@ class Console {
         }
         defer { _ = _close(slaveFD) }
 
+        try Terminal(descriptor: slaveFD, setInitState: false).setraw()
+
         for fd: Int32 in 0...2 {
             guard dup3(slaveFD, fd, 0) != -1 else {
                 throw App.Errno(stage: "dup3")

vminitd/Tests/vmexecTests/ConsoleTests.swift

@@ -0,0 +1,87 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2026 Apple Inc. and the Containerization project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+#if os(Linux)
+
+import Glibc
+import Testing
+@testable import vmexec
+
+@Suite("vmexec Console")
+struct ConsoleTests {
+    @Test("configureStdIO preserves output larger than the tty buffer")
+    func configureStdIOPreservesLargeOutput() throws {
+        let console = try Console()
+        defer { try? console.close() }
+
+        let expected = [UInt8](repeating: 0x61, count: 4096)
+        let child = fork()
+        #expect(child >= 0)
+        guard child >= 0 else { return }
+
+        if child == 0 {
+            do {
+                try console.configureStdIO()
+                expected.withUnsafeBytes { bytes in
+                    guard let baseAddress = bytes.baseAddress else { _exit(1) }
+                    var written = 0
+                    while written < bytes.count {
+                        let result = Glibc.write(
+                            STDOUT_FILENO,
+                            baseAddress.advanced(by: written),
+                            bytes.count - written
+                        )
+                        guard result > 0 else { _exit(1) }
+                        written += result
+                    }
+                    _exit(0)
+                }
+            } catch {
+                _exit(1)
+            }
+        }
+
+        var received: [UInt8] = []
+        received.reserveCapacity(expected.count)
+        while received.count < expected.count {
+            var descriptor = pollfd(fd: console.master, events: Int16(POLLIN), revents: 0)
+            let ready = poll(&descriptor, 1, 5_000)
+            #expect(ready >= 0)
+            guard ready > 0 else { break }
+
+            var buffer = [UInt8](repeating: 0, count: 1024)
+            let result = buffer.withUnsafeMutableBytes { bytes in
+                guard let baseAddress = bytes.baseAddress else { return -1 }
+                return Glibc.read(console.master, baseAddress, bytes.count)
+            }
+            if result > 0 {
+                received.append(contentsOf: buffer.prefix(Int(result)))
+            } else if result == -1 && errno == EINTR {
+                continue
+            } else {
+                break
+            }
+        }
+
+        var status: Int32 = 0
+        #expect(waitpid(child, &status, 0) == child)
+        #expect((status & 0x7f) == 0)
+        #expect(((status >> 8) & 0xff) == 0)
+        #expect(received == expected)
+    }
+}
+
+#endif