fix: vminitd incorrectly overwrites custom HOME environment variable (#136)

## Summary

The vminitd service was using `process.env.contains("HOME")` which
checks for exact string match rather than environment variables starting
with "HOME=".

Since environment variables are stored as `"KEY=value"` strings, the
condition was always false, causing vminitd to always override custom
HOME values even when explicitly provided by the client.

## Changes

- Updates the logic in `vminitd/Sources/vminitd/Server+GRPC.swift` to
use `contains(where: { $0.hasPrefix("HOME=") })` to properly detect
existing HOME environment variables
- Adds regression test `testProcessCustomHomeEnvvar()` to verify that
custom HOME environment variables are preserved when provided by the
client

## Testing

The fix has been tested with the new integration test that:
  - Sets a custom HOME environment variable (`HOME=/tmp/custom/home`)
- Runs a shell command that outputs the HOME variable on the container
runtime
- Verifies the custom HOME value is preserved and not overwritten with
the default

## Environment

  - macOS: 26.0 (25A5279m)
  - Hardware: M4 Pro
  - Xcode: 26 beta
  - Swift: 6.2-dev

Fixes #135

Author: nandsha

CONTRIBUTORS.txt

@@ -16,6 +16,7 @@ John Logan (jglogan)
 Kathryn Baldauf (katiewasnothere)
 Madhu Venugopal (mavenugo)
 Michael Crosby (crosbymichael)
+Nandha Reddy (nandsha)
 Sidhartha Mani (wlan0)
 Tanweer Noor (tanweernoor)
 Ximena Perez Diaz (ximenanperez)

Sources/Integration/ProcessTests.swift

@@ -95,7 +95,7 @@ extension IntegrationSuite {
 
             guard String(data: buffer.data, encoding: .utf8) == "hi\n" else {
                 throw IntegrationError.assert(
-                    msg: "process should have returned on stdout 'hi' != '\(String(data: buffer.data, encoding: .utf8)!)")
+                    msg: "process should have returned on stdout 'hi' != '\(String(data: buffer.data, encoding: .utf8)!)'")
             }
         } catch {
             try? await container.stop()
@@ -257,7 +257,7 @@ extension IntegrationSuite {
 
         guard String(data: buffer.data, encoding: .utf8) == "\(expected)\n" else {
             throw IntegrationError.assert(
-                msg: "process should have returned on stdout '\(expected)' != '\(String(data: buffer.data, encoding: .utf8)!)")
+                msg: "process should have returned on stdout '\(expected)' != '\(String(data: buffer.data, encoding: .utf8)!)'")
         }
     }
 
@@ -299,6 +299,39 @@ extension IntegrationSuite {
         }
     }
 
+    func testProcessCustomHomeEnvvar() async throws {
+        let id = "test-process-custom-home-envvar"
+
+        let bs = try await bootstrap()
+        let container = LinuxContainer(id, rootfs: bs.rootfs, vmm: bs.vmm)
+
+        let customHomeEnvvar = "HOME=/tmp/custom/home"
+        container.environment = [customHomeEnvvar]
+        container.arguments = ["sh", "-c", "echo HOME=$HOME"]
+        container.user = .init(uid: 0, gid: 0)
+
+        let buffer = BufferWriter()
+        container.stdout = buffer
+
+        try await container.create()
+        try await container.start()
+
+        let status = try await container.wait()
+        try await container.stop()
+
+        guard status == 0 else {
+            throw IntegrationError.assert(msg: "process status \(status) != 0")
+        }
+
+        guard let output = String(data: buffer.data, encoding: .utf8) else {
+            throw IntegrationError.assert(msg: "failed to convert stdout to UTF8")
+        }
+
+        guard output.contains(customHomeEnvvar) else {
+            throw IntegrationError.assert(msg: "process should have preserved custom HOME environment variable, expected \(customHomeEnvvar), got: \(output)")
+        }
+    }
+
     func testHostname() async throws {
         let id = "test-container-hostname"
 
@@ -327,7 +360,7 @@ extension IntegrationSuite {
 
         guard String(data: buffer.data, encoding: .utf8) == "\(expected)\n" else {
             throw IntegrationError.assert(
-                msg: "process should have returned on stdout '\(expected)' != '\(String(data: buffer.data, encoding: .utf8)!)")
+                msg: "process should have returned on stdout '\(expected)' != '\(String(data: buffer.data, encoding: .utf8)!)'")
         }
     }
 }

Sources/Integration/Suite.swift

@@ -199,6 +199,7 @@ struct IntegrationSuite: AsyncParsableCommand {
             "process echo hi": testProcessEchoHi,
             "process user": testProcessUser,
             "process home envvar": testProcessHomeEnvvar,
+            "process custom home envvar": testProcessCustomHomeEnvvar,
             "multiple concurrent processes": testMultipleConcurrentProcesses,
             "multiple concurrent processes with output stress": testMultipleConcurrentProcessesOutputStress,
             "container hostname": testHostname,

vminitd/Sources/vminitd/Server+GRPC.swift

@@ -846,7 +846,7 @@ extension Initd {
         process.user.uid = parsedUser.uid
         process.user.gid = parsedUser.gid
         process.user.additionalGids = parsedUser.sgids
-        if !process.env.contains("HOME") {
+        if !process.env.contains(where: { $0.hasPrefix("HOME=") }) {
             process.env.append("HOME=\(parsedUser.home)")
         }