Phase 4: Termux RUN_COMMAND bridge and su helper

app/src/main/java/io/github/abrarul/modularai/bridge/TermuxBridge.kt

@@ -0,0 +1,39 @@
+package io.github.abrarul.modularai.bridge
+
+import android.content.Context
+import android.content.Intent
+import android.content.pm.PackageManager
+
+/**
+ * Requires: Termux installed, `allow-external-apps = true` in ~/.termux/termux.properties,
+ * and the user granting com.termux.permission.RUN_COMMAND to this app.
+ */
+object TermuxBridge {
+    private const val PKG = "com.termux"
+    private const val SERVICE = "com.termux.app.RunCommandService"
+    private const val PREFIX = "/data/data/com.termux/files/usr"
+    private const val HOME = "/data/data/com.termux/files/home"
+
+    fun isInstalled(ctx: Context): Boolean = try {
+        ctx.packageManager.getPackageInfo(PKG, 0); true
+    } catch (_: PackageManager.NameNotFoundException) { false }
+
+    /** Runs [script] with bash inside Termux, in the background (no terminal session opened). */
+    fun run(ctx: Context, script: String, args: Array<String> = emptyArray()) {
+        val i = Intent("com.termux.RUN_COMMAND").apply {
+            setClassName(PKG, SERVICE)
+            putExtra("com.termux.RUN_COMMAND_PATH", "$PREFIX/bin/bash")
+            putExtra("com.termux.RUN_COMMAND_ARGUMENTS", arrayOf("-c", script) + args)
+            putExtra("com.termux.RUN_COMMAND_WORKDIR", HOME)
+            putExtra("com.termux.RUN_COMMAND_BACKGROUND", true)
+        }
+        ctx.startForegroundService(i)
+    }
+
+    /** Root is optional. Returns null when su is missing or denied. */
+    fun su(cmd: String): String? = try {
+        val p = ProcessBuilder("su", "-c", cmd).redirectErrorStream(true).start()
+        val out = p.inputStream.bufferedReader().readText()
+        if (p.waitFor() == 0) out else null
+    } catch (_: Exception) { null }
+}