Scan the enrollment QR in-app instead of relying on the camera app

Not every phone's camera app hands a scanned aiapp:// URI off to the app
reliably, which made enrollment an annoying multi-step process. The
Settings screen now scans the QR itself via zxing-android-embedded's
ScanContract (offline, no Play Services/ML Kit download) and feeds the
decoded URI through the existing parseEnrollmentUri. The aiapp://enroll
deep link stays as a fallback for cameras that do redirect.

Verified on the emulator: Scan QR code launches the scanner, prompts for
camera permission, shows a live preview, and backing out returns to
Settings cleanly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw

PLAN.md

@@ -334,10 +334,16 @@ complete path out of everything spawning one created.
     ANSI), encoding `aiapp://enroll?host=…&port=…&token=…`. The CA stays
     embedded in the APK (`PinnedCert.kt` pattern), so the QR carries no
     trust material — photographing the terminal leaks only the token
-    (rotatable), never a way to weaken pinning. The app side needs no QR
+    (rotatable), never a way to weaken pinning. The app registers an intent
-    library at all: it registers an intent filter for the `aiapp://enroll`
+    filter for the `aiapp://enroll` scheme as a fallback, for a camera app
-    scheme, and the stock camera app hands the scanned URI straight to
+    that redirects a scanned URI straight to `MainActivity` (2026-08-24).
-    `MainActivity` (2026-08-24).
+    That was meant to be the only path — "the app side needs no QR library
+    at all" — but reversed the same day: not every phone's stock camera
+    redirects a scanned URI to an app reliably, so the Settings screen also
+    scans in-app via `zxing-android-embedded`'s `ScanContract` (a ready-made
+    scanner Activity reached through the AndroidX Activity Result API,
+    fully offline, no Play Services/ML Kit model download) and feeds the
+    decoded URI to the same `parseEnrollmentUri` (2026-08-25).
   - **Storage**: server keeps only the SHA-256 in `config.json` (plain hash
     is enough for high-entropy random input; buys that a leaked config
     doesn't leak the credential). No "show token again" — lost means rotate.

app/androidApp/build.gradle.kts

@@ -126,4 +126,5 @@ dependencies {
     implementation(libs.compose.material3)
     implementation(libs.compose.ui)
     implementation(libs.androidx.activity.compose)
+    implementation(libs.zxing.embedded)
 }

app/androidApp/src/main/AndroidManifest.xml

@@ -27,8 +27,12 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
             <!-- Enrollment: the server prints its aiapp://enroll QR to the
-                 terminal; the phone's camera app opens the URI here, so no
+                 terminal. This intent filter is the fallback path for a
-                 camera code or QR library is needed in this app. -->
+                 camera app that redirects a scanned aiapp:// URI here
+                 directly; the Settings screen's own "Scan QR code" button
+                 (zxing-android-embedded) is the primary path and needs no
+                 filter, since it decodes the QR itself and hands the URI
+                 to parseEnrollmentUri in-process. -->
             <intent-filter>
                 <action android:name="android.intent.action.VIEW" />
                 <category android:name="android.intent.category.DEFAULT" />

app/androidApp/src/main/kotlin/com/example/aiapp/SettingsScreen.kt

@@ -1,5 +1,6 @@
 package com.example.aiapp
 
+import android.net.Uri
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
@@ -9,6 +10,7 @@ import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Button
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
@@ -21,12 +23,16 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.unit.dp
+import androidx.activity.compose.rememberLauncherForActivityResult
+import com.journeyapps.barcodescanner.ScanContract
+import com.journeyapps.barcodescanner.ScanIntentResult
+import com.journeyapps.barcodescanner.ScanOptions
 
 /**
- * Server address and token. The normal path is scanning the server's
+ * Server address and token. The normal path is the "Scan QR code" button
- * terminal QR (which lands in MainActivity and never shows this screen);
+ * below, which decodes the server's terminal QR itself; these fields are
- * these fields are the fallback for typing the same three values by hand.
+ * the fallback for typing the same three values by hand. [onBack] is null
- * [onBack] is null on first run, when there is nothing to go back to.
+ * on first run, when there is nothing to go back to.
  */
 @Composable
 fun SettingsScreen(
@@ -42,6 +48,19 @@ fun SettingsScreen(
     var token by remember { mutableStateOf("") }
     var error by remember { mutableStateOf<String?>(null) }
 
+    val scanLauncher = rememberLauncherForActivityResult(ScanContract()) { result: ScanIntentResult ->
+        // Null contents means the user backed out of the scanner -- not an
+        // error, so nothing to report.
+        val contents = result.contents ?: return@rememberLauncherForActivityResult
+        val settings = parseEnrollmentUri(Uri.parse(contents))
+        if (settings == null) {
+            error = "Not a valid enrollment code"
+        } else {
+            saveServerSettings(context, settings)
+            onSaved(settings)
+        }
+    }
+
     Column(Modifier.fillMaxSize().padding(16.dp)) {
         Row(verticalAlignment = Alignment.CenterVertically, modifier = Modifier.fillMaxWidth()) {
             Text(
@@ -55,13 +74,19 @@ fun SettingsScreen(
         }
         Spacer(Modifier.height(8.dp))
         Text(
-            "The easy way: run ai-server on the backend and scan the QR it prints " +
+            "The easy way: run ai-server on the backend and scan the QR it prints. " +
-                "with the phone's camera. Or type the same values here.",
+                "Or type the same values here.",
             style = MaterialTheme.typography.bodyMedium,
             color = MaterialTheme.colorScheme.onSurfaceVariant,
         )
         Spacer(Modifier.height(16.dp))
 
+        OutlinedButton(
+            onClick = { scanLauncher.launch(ScanOptions().setDesiredBarcodeFormats(ScanOptions.QR_CODE)) },
+            modifier = Modifier.fillMaxWidth(),
+        ) { Text("Scan QR code") }
+        Spacer(Modifier.height(16.dp))
+
         OutlinedTextField(
             value = host,
             onValueChange = { host = it },

app/gradle/libs.versions.toml

@@ -1,5 +1,6 @@
 # Latest stable versions as of 2026-08-24 (checked against Google Maven /
-# Maven Central; prereleases deliberately skipped).
+# Maven Central; prereleases deliberately skipped). zxing-embedded checked
+# 2026-08-25.
 [versions]
 agp = "9.3.2"
 kotlin = "2.4.10"
@@ -7,9 +8,15 @@ compose-multiplatform = "1.11.1"
 # material3 ships on its own release train, separate from the CMP version.
 compose-material3 = "1.9.0"
 androidx-activityCompose = "1.13.0"
+zxing-embedded = "4.3.0"
 
 [libraries]
 androidx-activity-compose = { module = "androidx.activity:activity-compose", version.ref = "androidx-activityCompose" }
+# In-app QR scanner: a ready-made scanning Activity (camera preview, runtime
+# permission prompt, flashlight toggle) reached through the AndroidX Activity
+# Result API (ScanContract, added in 4.3.0). Fully offline -- no Play
+# Services / ML Kit model download involved.
+zxing-embedded = { module = "com.journeyapps:zxing-android-embedded", version.ref = "zxing-embedded" }
 # Declared directly rather than through the plugin's `compose.*` accessors,
 # which are deprecated as of CMP 1.11.
 compose-runtime = { module = "org.jetbrains.compose.runtime:runtime", version.ref = "compose-multiplatform" }