Support E2B model discovery and improve load error messages

Model search now finds E4B, E2B, and generic gemma.litertlm in both
app storage and Downloads. Previously only E4B and generic were
checked, so E2B files were silently ignored ("model not found").

Load errors now hint at solutions (try E2B on low-RAM devices,
GPU init failure). Model variant logged on discovery.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vNeeL-code

app/src/main/kotlin/com/gemma/api/GemmaService.kt

@@ -681,17 +681,33 @@ class GemmaService : Service(), AgentPlatformCallbacks {
             val downloadDir = android.os.Environment.getExternalStoragePublicDirectory(
                 android.os.Environment.DIRECTORY_DOWNLOADS
             )
-            val modelFile = listOf(
-                // Check app storage first (survives Downloads cleanup)
-                File(getExternalFilesDir(null), "gemma-3n-E4B-it-int4.litertlm"),
-                File(getExternalFilesDir(null), "gemma.litertlm"),
-                // Fallback to Downloads
-                File(downloadDir, "gemma-3n-E4B-it-int4.litertlm"),
-                File(downloadDir, "gemma.litertlm")
-            ).firstOrNull { it.exists() }
+            // Search for any Gemma model variant (E4B preferred, E2B fallback, generic last)
+            val modelNames = listOf(
+                "gemma-3n-E4B-it-int4.litertlm",
+                "gemma-3n-E2B-it-int4.litertlm",
+                "gemma.litertlm"
+            )
+            val searchDirs = listOf(
+                getExternalFilesDir(null),  // App storage (survives Downloads cleanup)
+                downloadDir                  // Downloads folder
+            )
+            val modelFile = searchDirs.flatMap { dir ->
+                modelNames.map { name -> File(dir, name) }
+            }.firstOrNull { it.exists() }
+
+            if (modelFile != null) {
+                val variant = when {
+                    modelFile.name.contains("E4B") -> "E4B (full)"
+                    modelFile.name.contains("E2B") -> "E2B (lite)"
+                    else -> "unknown variant"
+                }
+                Timber.i("📦 Found model: ${modelFile.name} ($variant) in ${modelFile.parent}")
+            }
 
             if (modelFile == null) {
-                updateNotification("ERROR: No model found")
+                val searchedPaths = searchDirs.mapNotNull { it?.absolutePath }
+                Timber.e("No model found! Searched: $searchedPaths for: $modelNames")
+                updateNotification("ERROR: No model found. Place .litertlm in app folder or Downloads")
                 return
             }
 
@@ -700,7 +716,15 @@ class GemmaService : Service(), AgentPlatformCallbacks {
             // Inject Identity Prompt (Static)
             val error = newEngine.initialize(modelFile.absolutePath, com.gemma.api.logic.ContextManager.BASE_SYSTEM_PROMPT)
             if (error != null) {
-                updateNotification("Load Error: $error")
+                val hint = when {
+                    error.contains("memory", ignoreCase = true) || error.contains("OOM", ignoreCase = true) ->
+                        " (Try E2B model on this device)"
+                    error.contains("GPU", ignoreCase = true) ->
+                        " (GPU init failed — device may not support this model)"
+                    else -> ""
+                }
+                Timber.e("Model load failed: $error")
+                updateNotification("Load Error: ${error.take(80)}$hint")
                 return
             }