feat(app): add the single-activity Compose host

Its two routes hand off to the legacy list and decrypt activities until
those screens are ported.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2 files changed, 81 insertions, 0 deletions

diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 1cbe76a9..457647d5 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -65,6 +65,10 @@
     </activity>
 
     <activity
+      android:name=".ui.main.MainActivity"
+      android:exported="false" />
+
+    <activity
       android:name="com.journeyapps.barcodescanner.CaptureActivity"
       android:clearTaskOnLaunch="true"
       android:exported="false"
diff --git a/app/src/main/java/app/passwordstore/ui/main/MainActivity.kt b/app/src/main/java/app/passwordstore/ui/main/MainActivity.kt
new file mode 100644
index 00000000..018deae3
--- /dev/null
+++ b/app/src/main/java/app/passwordstore/ui/main/MainActivity.kt
@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+package app.passwordstore.ui.main
+
+import android.content.Intent
+import android.os.Bundle
+import androidx.activity.compose.setContent
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.fragment.app.FragmentActivity
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
+import androidx.navigation.toRoute
+import app.passwordstore.data.repo.PasswordRepository
+import app.passwordstore.ui.compose.theme.APSTheme
+import app.passwordstore.ui.crypto.BasePGPActivity
+import app.passwordstore.ui.crypto.DecryptActivity
+import app.passwordstore.ui.passwords.PasswordStore
+import dagger.hilt.android.AndroidEntryPoint
+import kotlinx.serialization.Serializable
+
+/** The password list, at the store root. */
+@Serializable data object ListRoute
+
+/** One entry. [filePath] was checked with [LaunchActivity.isFileInRepo] before routing here. */
+@Serializable data class EntryRoute(val filePath: String)
+
+/**
+ * Single-activity host for the Compose UI. Not exported: it is only started by [LaunchActivity],
+ * after its biometric gate and path check. Extends [FragmentActivity] only because BiometricPrompt
+ * needs one; it hosts no fragments.
+ */
+@AndroidEntryPoint
+class MainActivity : FragmentActivity() {
+
+  override fun onCreate(savedInstanceState: Bundle?) {
+    super.onCreate(savedInstanceState)
+    val filePath = intent.getStringExtra(BasePGPActivity.EXTRA_FILE_PATH)
+    val start: Any = if (filePath != null) EntryRoute(filePath) else ListRoute
+    setContent {
+      APSTheme {
+        NavHost(rememberNavController(), startDestination = start) {
+          composable<ListRoute> {
+            LegacyScreen(
+              Intent(this@MainActivity, PasswordStore::class.java).setAction(Intent.ACTION_VIEW)
+            )
+          }
+          composable<EntryRoute> { entry ->
+            val route = entry.toRoute<EntryRoute>()
+            LegacyScreen(
+              Intent(this@MainActivity, DecryptActivity::class.java)
+                .putExtra(BasePGPActivity.EXTRA_FILE_PATH, route.filePath)
+                .putExtra(
+                  BasePGPActivity.EXTRA_REPO_PATH,
+                  PasswordRepository.getRepositoryDirectory().absolutePath,
+                )
+            )
+          }
+        }
+      }
+    }
+  }
+
+  // ponytail: trampoline to a screen not yet ported; each port replaces one call with the
+  // real composable, and the last port deletes this function.
+  @Composable
+  private fun LegacyScreen(intent: Intent) {
+    LaunchedEffect(Unit) {
+      startActivity(intent)
+      finish()
+    }
+  }
+}