Refresh native Git helper aliases after app upgrade

- Rebuild the app-private git-exec helper directory when the packaged native Git binary changes.
- Remove stale helper aliases before recreating symlinks/copies.
- Add regression coverage for refreshing cached Git exec aliases across binary changes.

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

@@ -852,6 +852,7 @@ class GitRepositoryRuntime private constructor(
         } else {
             File(binary.parentFile ?: binary.absoluteFile.parentFile ?: sandboxesRoot, "git-exec")
         }
+        refreshGitExecDirectoryIfNeeded(directory, binary)
         directory.mkdirs()
 
         File(directory, "git").also { alias ->
@@ -870,7 +871,27 @@ class GitRepositoryRuntime private constructor(
         return directory
     }
 
+    private fun refreshGitExecDirectoryIfNeeded(directory: File, binary: File) {
+        val fingerprint = buildString {
+            append(binary.absolutePath)
+            append('\n')
+            append(binary.length())
+            append('\n')
+            append(binary.lastModified())
+        }
+        val stamp = File(directory, ".binary-fingerprint")
+        val previousFingerprint = stamp.takeIf { it.isFile }?.readText()
+        if (previousFingerprint != fingerprint) {
+            directory.deleteRecursively()
+        }
+        directory.mkdirs()
+        stamp.writeText(fingerprint)
+    }
+
     private fun createGitAlias(binary: File, alias: File) {
+        if (alias.exists() || Files.isSymbolicLink(alias.toPath())) {
+            alias.delete()
+        }
         if (context != null) {
             try {
                 Os.symlink(binary.absolutePath, alias.absolutePath)