Route interactive Git through native terminal sessions

Remove Kotlin interactive-add emulation and run patch add via the native Git runtime with PTY-backed session IO.

app/src/test/java/solutions/tretter/githugandroid/GitSandboxEngineTest.kt

@@ -535,6 +535,59 @@ class GitSandboxEngineTest {
         }
     }
 
+    @Test
+    fun nativeInteractiveAddKeepsCompiledGitSessionOpenForInput() {
+        val git = testGitBinary()
+        assumeTrue(git.exists() && git.canExecute())
+        val root = Files.createTempDirectory("githug-native-add-i").toFile()
+        try {
+            val runtime = GitRepositoryRuntime(root, git)
+            val level = addLevel()
+            var repo = runtime.prepareLevel(level)
+
+            val (menuRepo, menuOutput) = runtime.execute(level, repo, "git add -i")
+            repo = menuRepo
+            val (quitRepo, quitOutput) = runtime.execute(level, repo, "q")
+
+            assertNotNull(menuRepo.nativeGitSession)
+            assertTrue(menuOutput.joinToString("\n"), menuOutput.any { it.contains("What now") })
+            assertNull(quitRepo.nativeGitSession)
+            assertTrue(quitOutput.joinToString("\n"), quitOutput.any { it.contains("Bye") })
+        } finally {
+            root.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun nativePatchAddUsesCompiledGitEditorAndStagesOnlyEditedStageLinesHunk() {
+        val git = testGitBinary()
+        assumeTrue(git.exists() && git.canExecute())
+        val root = Files.createTempDirectory("githug-stage-lines-native-patch").toFile()
+        try {
+            val runtime = GitRepositoryRuntime(root, git)
+            val level = stageLinesLevel()
+            var repo = runtime.prepareLevel(level)
+
+            val (patchRepo, patchOutput) = runtime.execute(
+                level,
+                repo,
+                "GIT_EDITOR=\"sed -i '/second feature/d'\" git add -p feature.rb",
+            )
+            repo = patchRepo
+            val (resultRepo, _) = runtime.execute(level, repo, "e")
+            val file = resultRepo.files.single { it.name == "feature.rb" }
+
+            assertNotNull(patchRepo.nativeGitSession)
+            assertTrue(patchOutput.joinToString("\n"), patchOutput.any { it.contains("Stage this hunk") })
+            assertNull(resultRepo.nativeGitSession)
+            assertTrue(resultRepo.diagnosticSnapshot(), level.validator(resultRepo, "e"))
+            assertTrue(file.stagedContent.orEmpty(), file.stagedContent.orEmpty().contains("This change belongs to the first feature"))
+            assertFalse(file.stagedContent.orEmpty(), file.stagedContent.orEmpty().contains("This change belongs to the second feature"))
+        } finally {
+            root.deleteRecursively()
+        }
+    }
+
     private fun testGitBinary(): File {
         System.getenv("GITHUG_TEST_GIT_BINARY")
             ?.takeIf { it.isNotBlank() }