lib: add UnsupportedArchitectureException for triaged error message

examples/llama.android/app/src/main/java/com/example/llama/engine/StubInferenceEngine.kt

@@ -80,7 +80,7 @@ class StubInferenceEngine : InferenceEngine {
                 // If coroutine is cancelled, propagate cancellation
                 throw e
             } catch (e: Exception) {
-                _state.value = State.Error(e.message ?: "Unknown error during model loading")
+                _state.value = State.Error(e)
             }
         }
 
@@ -107,7 +107,7 @@ class StubInferenceEngine : InferenceEngine {
                 // If coroutine is cancelled, propagate cancellation
                 throw e
             } catch (e: Exception) {
-                _state.value = State.Error(e.message ?: "Unknown error during model loading")
+                _state.value = State.Error(e)
             }
         }
 
@@ -142,13 +142,13 @@ class StubInferenceEngine : InferenceEngine {
             _state.value = State.ModelReady
             throw e
         } catch (e: Exception) {
-            _state.value = State.Error(e.message ?: "Unknown error during generation")
+            _state.value = State.Error(e)
             throw e
         }
     }.catch { e ->
         // If it's not a cancellation, update state to error
         if (e !is CancellationException) {
-            _state.value = State.Error(e.message ?: "Unknown error during generation")
+            _state.value = State.Error(Exception(e))
         }
         throw e
     }
@@ -198,7 +198,7 @@ class StubInferenceEngine : InferenceEngine {
                 _state.value = State.ModelReady
                 throw e
             } catch (e: Exception) {
-                _state.value = State.Error(e.message ?: "Unknown error during benchmarking")
+                _state.value = State.Error(e)
                 "Error: ${e.message}"
             }
         }

examples/llama.android/app/src/main/java/com/example/llama/ui/screens/ModelLoadingScreen.kt

@@ -1,6 +1,7 @@
 package com.example.llama.ui.screens
 
 import android.llama.cpp.InferenceEngine.State
+import android.llama.cpp.UnsupportedArchitectureException
 import androidx.activity.compose.BackHandler
 import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.animation.expandVertically
@@ -112,7 +113,7 @@ fun ModelLoadingScreen(
 
     // Check if we're in a loading state
     val isLoading = engineState !is State.Initialized && engineState !is State.ModelReady
-    val errorMessage = (engineState as? State.Error)?.errorMessage
+    val exception = (engineState as? State.Error)?.exception
 
     // Handle back navigation requests
     BackHandler {
@@ -331,7 +332,7 @@ fun ModelLoadingScreen(
                 }
             },
             modifier = Modifier.fillMaxWidth().height(56.dp),
-            colors = if (errorMessage != null)
+            colors = if (exception != null)
                 ButtonDefaults.buttonColors(
                     disabledContainerColor = MaterialTheme.colorScheme.errorContainer.copy(alpha = 0.3f),
                     disabledContentColor   = MaterialTheme.colorScheme.onErrorContainer.copy(alpha = 0.7f)
@@ -340,15 +341,21 @@ fun ModelLoadingScreen(
                 (!useSystemPrompt || hasActiveSystemPrompt)
         ) {
             when {
-                errorMessage != null -> {
+                exception != null -> {
+                    val message = if (exception is UnsupportedArchitectureException) {
+                        "Unsupported architecture: ${selectedModel?.metadata?.architecture?.architecture}"
+                    } else {
+                        exception.message ?: "Unknown error"
+                    }
+
                     Icon(
                         imageVector = Icons.Default.Error,
-                        contentDescription = errorMessage,
+                        contentDescription = message,
                         tint = MaterialTheme.colorScheme.error
                     )
                     Spacer(modifier = Modifier.width(8.dp))
                     Text(
-                        text = errorMessage,
+                        text = message,
                         color = MaterialTheme.colorScheme.onErrorContainer
                     )
                 }

examples/llama.android/llama/src/main/java/android/llama/cpp/InferenceEngine.kt

@@ -15,6 +15,8 @@ interface InferenceEngine {
 
     /**
      * Load a model from the given path.
+     *
+     * @throws UnsupportedArchitectureException if model architecture not supported
      */
     suspend fun loadModel(pathToModel: String)
 
@@ -61,7 +63,7 @@ interface InferenceEngine {
 
         object Generating : State()
 
-        data class Error(val errorMessage: String = "") : State()
+        data class Error(val exception: Exception) : State()
     }
 
     companion object {
@@ -81,3 +83,5 @@ val State.isModelLoaded: Boolean
         this !is State.Initialized &&
         this !is State.LoadingModel &&
         this !is State.UnloadingModel
+
+class UnsupportedArchitectureException : Exception()

examples/llama.android/llama/src/main/java/android/llama/cpp/internal/InferenceEngineImpl.kt

@@ -2,6 +2,7 @@ package android.llama.cpp.internal
 
 import android.llama.cpp.InferenceEngine
 import android.llama.cpp.LLamaTier
+import android.llama.cpp.UnsupportedArchitectureException
 import android.util.Log
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CoroutineScope
@@ -143,7 +144,7 @@ internal class InferenceEngineImpl private constructor(
                 _state.value = InferenceEngine.State.LoadingModel
                 load(pathToModel).let {
                     // TODO-han.yin: find a better way to pass other error codes
-                    if (it != 0) throw IOException("Unsupported architecture")
+                    if (it != 0) throw UnsupportedArchitectureException()
                 }
                 prepare().let {
                     if (it != 0) throw IOException("Failed to prepare resources")
@@ -152,9 +153,8 @@ internal class InferenceEngineImpl private constructor(
                 _readyForSystemPrompt = true
                 _state.value = InferenceEngine.State.ModelReady
             } catch (e: Exception) {
-                val msg = e.message ?: "Unknown error"
+                Log.e(TAG, (e.message ?: "Error loading model") + "\n" + pathToModel, e)
-                Log.e(TAG, msg + "\n" + pathToModel, e)
+                _state.value = InferenceEngine.State.Error(e)
-                _state.value = InferenceEngine.State.Error(msg)
                 throw e
             }
         }
@@ -177,9 +177,10 @@ internal class InferenceEngineImpl private constructor(
             _state.value = InferenceEngine.State.ProcessingSystemPrompt
             processSystemPrompt(prompt).let { result ->
                 if (result != 0) {
-                    val errorMessage = "Failed to process system prompt: $result"
+                    RuntimeException("Failed to process system prompt: $result").also {
-                    _state.value = InferenceEngine.State.Error(errorMessage)
+                        _state.value = InferenceEngine.State.Error(it)
-                    throw IllegalStateException(errorMessage)
+                        throw it
+                    }
                 }
             }
             Log.i(TAG, "System prompt processed! Awaiting user prompt...")
@@ -225,7 +226,7 @@ internal class InferenceEngineImpl private constructor(
             throw e
         } catch (e: Exception) {
             Log.e(TAG, "Error during generation!", e)
-            _state.value = InferenceEngine.State.Error(e.message ?: "Unknown error")
+            _state.value = InferenceEngine.State.Error(e)
             throw e
         }
     }.flowOn(llamaDispatcher)