Create packaged Git exec aliases for helper commands

- Create a runtime git-exec directory containing git-* aliases that point at the packaged libgit.so binary.
- Set GIT_EXEC_PATH for every native Git invocation so Git subcommands like fetch, merge-base, upload-pack, and receive-pack resolve the same way in tests and on-device.
- Keep JVM tests on GitRepositoryRuntime with the compiled host libgit.so so Push exercises the packaged-runtime execution model.

app/src/main/java/solutions/tretter/githugandroid/GitRuntime.kt

@@ -2,7 +2,9 @@ package solutions.tretter.githugandroid
 
 import android.os.Build
 import android.content.Context
+import android.system.Os
 import java.io.File
+import java.nio.file.Files
 
 class GitRepositoryRuntime private constructor(
     private val context: Context?,
@@ -11,6 +13,34 @@ class GitRepositoryRuntime private constructor(
 ) {
     private companion object {
         const val SyntheticRemoteUrl = "remote"
+        val RequiredGitCommandAliases = listOf(
+            "add",
+            "branch",
+            "checkout",
+            "commit",
+            "commit-tree",
+            "config",
+            "diff",
+            "fetch",
+            "index-pack",
+            "merge",
+            "merge-base",
+            "pack-objects",
+            "pull",
+            "push",
+            "read-tree",
+            "rebase",
+            "receive-pack",
+            "rev-list",
+            "rev-parse",
+            "show-ref",
+            "stash",
+            "status",
+            "symbolic-ref",
+            "unpack-objects",
+            "update-ref",
+            "upload-pack",
+        )
     }
 
     constructor(context: Context) : this(
@@ -816,11 +846,13 @@ class GitRepositoryRuntime private constructor(
 
     private fun runProcess(binary: File, workingDir: File, arguments: List<String>): ProcessExecutionResult {
         return try {
+            val gitExecPath = gitExecDirectory(binary)
             val process = ProcessBuilder(listOf(binary.absolutePath) + arguments)
                 .directory(workingDir)
                 .redirectErrorStream(true)
                 .apply {
                     environment()["HOME"] = workingDir.absolutePath
+                    environment()["GIT_EXEC_PATH"] = gitExecPath.absolutePath
                     environment()["GIT_CONFIG_NOSYSTEM"] = "1"
                     environment()["GIT_AUTHOR_NAME"] = "GitHug"
                     environment()["GIT_AUTHOR_EMAIL"] = "githug@example.com"
@@ -837,6 +869,42 @@ class GitRepositoryRuntime private constructor(
             ProcessExecutionResult(exitCode = -1, outputLines = listOf("Native Git execution failed: ${error.message ?: error::class.java.simpleName}"))
         }
     }
+
+    private fun gitExecDirectory(binary: File): File {
+        val directory = if (context != null) {
+            File(context.filesDir, "git-exec")
+        } else {
+            File(binary.parentFile ?: binary.absoluteFile.parentFile ?: sandboxesRoot, "git-exec")
+        }
+        directory.mkdirs()
+
+        RequiredGitCommandAliases.forEach { command ->
+            val alias = File(directory, "git-$command")
+            if (!alias.exists()) {
+                createGitAlias(binary, alias)
+            }
+        }
+        return directory
+    }
+
+    private fun createGitAlias(binary: File, alias: File) {
+        if (context != null) {
+            try {
+                Os.symlink(binary.absolutePath, alias.absolutePath)
+                alias.setExecutable(true, false)
+                return
+            } catch (_: Exception) {
+                // Fall through to the portable options below.
+            }
+        }
+
+        try {
+            Files.createSymbolicLink(alias.toPath(), binary.toPath())
+        } catch (_: Exception) {
+            binary.copyTo(alias, overwrite = true)
+        }
+        alias.setExecutable(true, false)
+    }
 }
 
 private data class ProcessExecutionResult(