fix: address PR #475 review comments — 6 fixes across Flutter config validation

- **QEF-1 (greptile P1, `dart_bridge_llm.dart:390`)**: `_requireLoadedContextLength()`
  no longer throws `SDKError.validationFailed` when the loaded model lacks
  `contextLength` metadata. Falls back to `32768` (a generous ceiling) so
  generation isn't silently broken for models that were registered without a
  non-zero `contextLength` in their C struct. Return type stays `int`
  (non-nullable) so call sites don't need to change; `SDKError` import dropped.

- **QEF-2 / QEF-5 / QEF-7 (greptile P1 + coderabbit Critical ×2, `llm_configuration.dart:30`)**:
  Removed the hardcoded 32 768 ceiling on `contextLength` from
  `LLMConfiguration.validate()`. The previous `contextLength > 32768` rejection
  blocked every generation attempt on modern large-context models (Llama 3.1 8B
  at 128K, Mistral v0.3 at 32K, etc.). Kept only `contextLength <= 0`; the
  existing `maxTokens <= contextLength` check provides the effective upper
  bound. Error message updated to "Context length must be greater than 0".

- **QEF-3 (greptile P2, `dart_bridge_model_registry.dart:200`)**: The
  `model.contextLength ?? 0` pattern in `savePublicModel` is in fact correct —
  `public_types.ModelInfo.contextLength` IS nullable (`int?`), and the internal
  `RacModelInfoCStruct.contextLength` is non-nullable `int` with `0` as the
  "missing" sentinel that `_ffiModelToPublic` maps back to `null`. Added a doc
  comment at the adapter boundary explaining the null↔zero convention so the
  intent is obvious and the reverse conversion is linked.

- **QEF-4 (coderabbit Major, `llm_configuration.dart:48`)**: Added `systemPrompt`
  length validation to `validate()`. Oversized prompts (a system prompt longer
  than the model's context window, measured roughly as `contextLength * 4` chars
  at ~4 chars/token) are now rejected before the FFI call with a descriptive
  error. Null `systemPrompt` is still allowed.

- **QEF-6 (coderabbit Minor, `tts_configuration.dart:16`)**: Aligned the
  default `speakingRate` from `0.5` to `1.0` so `const TTSConfiguration()`
  matches `dart_bridge_tts.synthesize()`'s default rate. The `validate()`
  range (0.5–2.0) still admits 1.0, no range change needed.

- **QEF-8 (coderabbit Major, `dart_bridge_model_assignment.dart:257` +
  `dart_bridge_model_registry.dart:1040`)**: `_structToModelInfo` now
  propagates `contextLength` into the returned `ModelInfo`, so models loaded
  via the assignment/discovery flow carry the metadata that the LLM bridge's
  `_requireLoadedContextLength()` relies on. Added the corresponding
  `contextLength` field to `RacModelInfoStruct` to match the C layout read
  by this path.

- **Cleanup**: removed 4 redundant `!` operators on `systemPromptPtr` in
  `dart_bridge_llm.dart` (lines 532, 599, 668, 704) and wrapped two
  non-awaited `controller.close()` calls in `unawaited(...)` (lines 357,
  361) so `flutter analyze` reports a clean run on the modified files.

**Invalid / superseded by code evolution:** none (all comments addressed).

**Verification:** `flutter analyze` on the five modified files reports
"No issues found!" with Flutter 3.38.3 / Dart 3.10.1. The older `dart analyze`
(Dart 2.17.3, pre-Dart 3) still reports pre-existing "Future isn't a type"
cascades because the repo requires Dart >=3.0.0 — that's an environment issue,
not a code issue.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sanchitmonga22

sdk/runanywhere-flutter/packages/runanywhere/lib/features/llm/llm_configuration.dart

@@ -27,9 +27,9 @@ class LLMConfiguration implements ComponentConfiguration {
 
   @override
   void validate() {
-    if (contextLength <= 0 || contextLength > 32768) {
+    if (contextLength <= 0) {
       throw SDKError.validationFailed(
-        'Context length must be between 1 and 32768',
+        'Context length must be greater than 0',
       );
     }
 
@@ -44,5 +44,15 @@ class LLMConfiguration implements ComponentConfiguration {
         'Max tokens must be between 1 and context length',
       );
     }
+
+    // Guard against clearly oversized prompts (chars) — a system prompt larger
+    // than the model's context window (in chars) is clearly invalid.
+    // Uses ~4 chars per token as a generous char-level bound.
+    final prompt = systemPrompt;
+    if (prompt != null && prompt.length > contextLength * 4) {
+      throw SDKError.validationFailed(
+        "systemPrompt length (${prompt.length} chars) exceeds the model's context window",
+      );
+    }
   }
 }

sdk/runanywhere-flutter/packages/runanywhere/lib/features/tts/tts_configuration.dart

@@ -13,7 +13,7 @@ class TTSConfiguration implements ComponentConfiguration {
   const TTSConfiguration({
     this.voice = 'system',
     this.language = 'en-US',
-    this.speakingRate = 0.5,
+    this.speakingRate = 1.0,
     this.pitch = 1.0,
     this.volume = 1.0,
     this.audioFormat = 'pcm',

sdk/runanywhere-flutter/packages/runanywhere/lib/native/dart_bridge_llm.dart

@@ -19,7 +19,6 @@ import 'dart:isolate'; // Keep for non-streaming generation
 
 import 'package:ffi/ffi.dart';
 import 'package:runanywhere/features/llm/llm_configuration.dart';
-import 'package:runanywhere/foundation/error_types/sdk_error.dart';
 import 'package:runanywhere/foundation/logging/sdk_logger.dart';
 import 'package:runanywhere/native/ffi_types.dart';
 import 'package:runanywhere/native/platform_loader.dart';
@@ -355,11 +354,11 @@ class DartBridgeLLM {
         controller.add(message);
       } else if (message is _StreamingMessage) {
         if (message.isComplete) {
-          controller.close();
+          unawaited(controller.close());
           receivePort.close();
         } else if (message.error != null) {
           controller.addError(StateError(message.error!));
-          controller.close();
+          unawaited(controller.close());
           receivePort.close();
         }
       }
@@ -389,13 +388,9 @@ class DartBridgeLLM {
 
   int _requireLoadedContextLength() {
     final contextLength = _loadedContextLength;
-    if (contextLength != null && contextLength > 0) {
-      return contextLength;
-    }
-
-    throw SDKError.validationFailed(
-      'Loaded model is missing context length metadata for maxTokens validation',
-    );
+    // Fall back to a generous ceiling when registry metadata is absent,
+    // so generation is not blocked for models without explicit contextLength.
+    return (contextLength != null && contextLength > 0) ? contextLength : 32768;
   }
 
   void _validateGenerationParameters({
@@ -534,7 +529,7 @@ void _streamingIsolateEntry(_StreamingIsolateParams params) {
     // Set systemPrompt if provided
     if (params.systemPrompt != null && params.systemPrompt!.isNotEmpty) {
       systemPromptPtr = params.systemPrompt!.toNativeUtf8();
-      optionsPtr.ref.systemPrompt = systemPromptPtr!;
+      optionsPtr.ref.systemPrompt = systemPromptPtr;
     } else {
       optionsPtr.ref.systemPrompt = nullptr;
     }
@@ -601,7 +596,7 @@ void _streamingIsolateEntry(_StreamingIsolateParams params) {
     calloc.free(promptPtr);
     calloc.free(optionsPtr);
     if (systemPromptPtr != null) {
-      calloc.free(systemPromptPtr!);
+      calloc.free(systemPromptPtr);
     }
     _isolateSendPort = null;
   }
@@ -670,7 +665,7 @@ _IsolateGenerationResult _generateInIsolate(
     // Set systemPrompt if provided
     if (systemPrompt != null && systemPrompt.isNotEmpty) {
       systemPromptPtr = systemPrompt.toNativeUtf8();
-      optionsPtr.ref.systemPrompt = systemPromptPtr!;
+      optionsPtr.ref.systemPrompt = systemPromptPtr;
     } else {
       optionsPtr.ref.systemPrompt = nullptr;
     }
@@ -706,7 +701,7 @@ _IsolateGenerationResult _generateInIsolate(
     calloc.free(optionsPtr);
     calloc.free(resultPtr);
     if (systemPromptPtr != null) {
-      calloc.free(systemPromptPtr!);
+      calloc.free(systemPromptPtr);
     }
   }
 }

sdk/runanywhere-flutter/packages/runanywhere/lib/native/dart_bridge_model_assignment.dart

@@ -253,6 +253,7 @@ class DartBridgeModelAssignment {
       framework: struct.ref.framework,
       source: struct.ref.source,
       sizeBytes: struct.ref.sizeBytes,
+      contextLength: struct.ref.contextLength,
       downloadURL: struct.ref.downloadURL != nullptr
           ? struct.ref.downloadURL.toDartString()
           : null,

sdk/runanywhere-flutter/packages/runanywhere/lib/native/dart_bridge_model_registry.dart

@@ -188,7 +188,15 @@ class DartBridgeModelRegistry {
     }
 
     try {
-      // Convert public ModelInfo to FFI ModelInfo
+      // Convert public ModelInfo to FFI ModelInfo.
+      //
+      // Nullable -> non-nullable at the adapter boundary:
+      //   public_types.ModelInfo.downloadSize and .contextLength are `int?`
+      //   (null means "unknown"), while the internal FFI ModelInfo uses
+      //   non-nullable `int` to mirror the C struct (which uses 0 as the
+      //   sentinel for "unset"). The `?? 0` here encodes that null -> 0
+      //   convention; the reverse conversion in `_ffiModelToPublic` maps
+      //   `> 0 ? value : null` back to public types.
       final ffiModel = ModelInfo(
         id: model.id,
         name: model.name,
@@ -1036,6 +1044,9 @@ base class RacModelInfoStruct extends Struct {
   @Int64()
   external int sizeBytes;
 
+  @Int32()
+  external int contextLength;
+
   external Pointer<Utf8> downloadURL;
   external Pointer<Utf8> localPath;
   external Pointer<Utf8> version;