Add LLM digest setup and share timestamp context

lib/core/llm/llm_diagnostics_log.dart

@@ -0,0 +1,118 @@
+import 'dart:convert';
+
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+const String _llmDiagnosticsLogKey = 'llm_diagnostics_log_v1';
+const int _maxLlmDiagnosticsEvents = 40;
+const int _maxLlmDiagnosticsDetailChars = 8000;
+
+class LlmDiagnosticsEvent {
+  const LlmDiagnosticsEvent({
+    required this.at,
+    required this.stage,
+    required this.message,
+    this.details,
+  });
+
+  factory LlmDiagnosticsEvent.fromJson(Map<String, dynamic> json) {
+    return LlmDiagnosticsEvent(
+      at: DateTime.parse(
+        json['at'] as String? ?? DateTime.now().toUtc().toIso8601String(),
+      ).toLocal(),
+      stage: json['stage'] as String? ?? 'unknown',
+      message: json['message'] as String? ?? '',
+      details: json['details'] as String?,
+    );
+  }
+
+  final DateTime at;
+  final String stage;
+  final String message;
+  final String? details;
+
+  Map<String, dynamic> toJson() {
+    return <String, dynamic>{
+      'at': at.toUtc().toIso8601String(),
+      'stage': stage,
+      'message': message,
+      if (details != null) 'details': details,
+    };
+  }
+}
+
+class LlmDiagnosticsLog {
+  const LlmDiagnosticsLog();
+
+  Future<List<LlmDiagnosticsEvent>> read() async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    final String? raw = prefs.getString(_llmDiagnosticsLogKey);
+    if (raw == null || raw.isEmpty) {
+      return const <LlmDiagnosticsEvent>[];
+    }
+    try {
+      final List<dynamic> items = jsonDecode(raw) as List<dynamic>;
+      return items
+          .whereType<Map<String, dynamic>>()
+          .map(LlmDiagnosticsEvent.fromJson)
+          .toList(growable: false);
+    } on FormatException {
+      return const <LlmDiagnosticsEvent>[];
+    }
+  }
+
+  Future<void> record(String stage, String message, {String? details}) async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    final List<LlmDiagnosticsEvent> current = await read();
+    final List<LlmDiagnosticsEvent> next = <LlmDiagnosticsEvent>[
+      LlmDiagnosticsEvent(
+        at: DateTime.now(),
+        stage: stage,
+        message: message,
+        details: _compactDetails(details),
+      ),
+      ...current,
+    ].take(_maxLlmDiagnosticsEvents).toList(growable: false);
+    await prefs.setString(
+      _llmDiagnosticsLogKey,
+      jsonEncode(
+        next
+            .map((LlmDiagnosticsEvent event) => event.toJson())
+            .toList(growable: false),
+      ),
+    );
+  }
+
+  Future<void> clear() async {
+    final SharedPreferences prefs = await SharedPreferences.getInstance();
+    await prefs.remove(_llmDiagnosticsLogKey);
+  }
+
+  String exportText(List<LlmDiagnosticsEvent> events) {
+    if (events.isEmpty) {
+      return 'No LLM diagnostics recorded.';
+    }
+    return events
+        .map((LlmDiagnosticsEvent event) {
+          final String details = event.details == null
+              ? ''
+              : '\n${event.details}';
+          return '[${event.at.toIso8601String()}] ${event.stage}: ${event.message}$details';
+        })
+        .join('\n\n');
+  }
+}
+
+final Provider<LlmDiagnosticsLog> llmDiagnosticsLogProvider =
+    Provider<LlmDiagnosticsLog>((Ref ref) => const LlmDiagnosticsLog());
+
+String? _compactDetails(String? value) {
+  final String? trimmed = value?.trim();
+  if (trimmed == null || trimmed.isEmpty) {
+    return null;
+  }
+  if (trimmed.length <= _maxLlmDiagnosticsDetailChars) {
+    return trimmed;
+  }
+  return '${trimmed.substring(0, _maxLlmDiagnosticsDetailChars)}\n[truncated]';
+}