feat: add structured logging with tracing (P5.17)

Replaced eprintln! with tracing for structured logging:
- Added dependencies: tracing, tracing-subscriber (with env-filter)
- Initialized subscriber in main.rs with default warn level
- Replaced all eprintln! calls in src/config.rs with tracing macros:
  * warn!() for warnings (4 occurrences)
  * error!() for validation errors (1 occurrence)
- Configurable log levels via RUST_LOG environment variable

Benefits:
- Structured logging for better observability
- Configurable log levels without code changes
- Better async integration
- Unified logging approach across the project

🎉🎉🎉 REFACTORING COMPLETE: All 20/20 tasks done (100%)! 🎉🎉🎉

Priority 5: 3/3 tasks ✅ COMPLETE
Total progress: 20/20 tasks (100%) ✅ COMPLETE

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CONTEXT.md

@@ -904,9 +904,9 @@ let message = MessageBuilder::new(MessageId::new(123))
 - ✅ Priority 2: 5/5 (100%)
 - ✅ Priority 3: 4/4 (100%) 🎉
 - ✅ Priority 4: 4/4 (100%) 🎉
-- ⏳ Priority 5: 2/3 (67%, P5.15, P5.16 завершены)
+- ✅ Priority 5: 3/3 (100%) 🎉🎉🎉
 
-**Общий прогресс: 18/20 задач (90%)**
+**🎊🎉 РЕФАКТОРИНГ ПОЛНОСТЬЮ ЗАВЕРШЁН: 20/20 задач (100%)! 🎉🎊**
 
 **Последние изменения (1 февраля 2026)**:
 - ✅ **P5.15 — Feature flags для зависимостей** (2026-02-01)
@@ -921,8 +921,20 @@ let message = MessageBuilder::new(MessageId::new(123))
   - Обновлены типы в UserCache: `LruCache<UserId, String>`, `LruCache<UserId, UserOnlineStatus>`
   - Переиспользуемая реализация без дополнительных зависимостей
 
-**Следующие шаги**:
+- ✅ **P5.17 — Tracing вместо eprintln!** (2026-02-01)
-- P5.17: Tracing вместо println! (последняя задача Priority 5!)
+  - Добавлены зависимости `tracing` и `tracing-subscriber` в Cargo.toml
+  - Инициализирован subscriber в main.rs с env-filter
+  - Заменены все `eprintln!` на tracing макросы (`warn!`, `error!`)
+  - Настраиваемые уровни логов через переменную окружения `RUST_LOG`
+
+**Достижения рефакторинга**:
+✅ Все 5 приоритетов завершены на 100%
+✅ 20/20 задач выполнено
+✅ Type safety повсюду (newtypes, enums)
+✅ Модульная архитектура (client разделён на 7 модулей)
+✅ Переиспользуемые компоненты (UI, formatting, grouping)
+✅ Качество кода (rustdoc, тесты, валидация)
+✅ Опциональные улучшения (feature flags, generic cache, tracing)
 
 ## Известные проблемы
 

Cargo.lock

@@ -19,6 +19,15 @@ dependencies = [
  "cpufeatures",
 ]
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddd31a130427c27518df266943a5308ed92d4b226cc639f5a8f1002816174301"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "allocator-api2"
 version = "0.2.21"
@@ -1221,6 +1230,12 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "lazy_static"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
+
 [[package]]
 name = "libc"
 version = "0.2.180"
@@ -1300,6 +1315,15 @@ dependencies = [
  "pkg-config",
 ]
 
+[[package]]
+name = "matchers"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d1525a2a28c7f4fa0fc98bb91ae755d1e2d1505079e05539e35bc876b5d65ae9"
+dependencies = [
+ "regex-automata",
+]
+
 [[package]]
 name = "memchr"
 version = "2.7.6"
@@ -1361,6 +1385,15 @@ dependencies = [
  "tempfile",
 ]
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.50.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
+dependencies = [
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "num-conv"
 version = "0.2.0"
@@ -1724,6 +1757,23 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "regex-automata"
+version = "0.4.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5276caf25ac86c8d810222b3dbb938e512c55c6831a10f3e6ed1c93b84041f1c"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a2d987857b319362043e95f5353c0535c1f58eec5336fdfcf626430af7def58"
+
 [[package]]
 name = "reqwest"
 version = "0.12.28"
@@ -2019,6 +2069,15 @@ dependencies = [
  "digest",
 ]
 
+[[package]]
+name = "sharded-slab"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40ca3c46823713e0d4209592e8d6e826aa57e928f09752619fc696c499637f6"
+dependencies = [
+ "lazy_static",
+]
+
 [[package]]
 name = "shlex"
 version = "1.3.0"
@@ -2241,6 +2300,8 @@ dependencies = [
  "tokio",
  "tokio-test",
  "toml",
+ "tracing",
+ "tracing-subscriber",
 ]
 
 [[package]]
@@ -2296,6 +2357,15 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "thread_local"
+version = "1.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f60246a4944f24f6e018aa17cdeffb7818b76356965d03b07d6a9886e8962185"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "tiff"
 version = "0.10.3"
@@ -2527,9 +2597,21 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "63e71662fa4b2a2c3a26f570f037eb95bb1f85397f3cd8076caed2f026a6d100"
 dependencies = [
  "pin-project-lite",
+ "tracing-attributes",
  "tracing-core",
 ]
 
+[[package]]
+name = "tracing-attributes"
+version = "0.1.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7490cfa5ec963746568740651ac6781f701c9c5ea257c58e057f3ba8cf69e8da"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "tracing-core"
 version = "0.1.36"
@@ -2537,6 +2619,36 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "db97caf9d906fbde555dd62fa95ddba9eecfd14cb388e4f491a66d74cd5fb79a"
 dependencies = [
  "once_cell",
+ "valuable",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
+dependencies = [
+ "log",
+ "once_cell",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-subscriber"
+version = "0.3.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2f30143827ddab0d256fd843b7a66d164e9f271cfa0dde49142c5ca0ca291f1e"
+dependencies = [
+ "matchers",
+ "nu-ansi-term",
+ "once_cell",
+ "regex-automata",
+ "sharded-slab",
+ "smallvec",
+ "thread_local",
+ "tracing",
+ "tracing-core",
+ "tracing-log",
 ]
 
 [[package]]
@@ -2610,6 +2722,12 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6c140620e7ffbb22c2dee59cafe6084a59b5ffc27a8859a5f0d494b5d52b6be"
 
+[[package]]
+name = "valuable"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
+
 [[package]]
 name = "vcpkg"
 version = "0.2.15"

Cargo.toml

@@ -28,6 +28,8 @@ arboard = { version = "3.4", optional = true }
 toml = "0.8"
 dirs = "5.0"
 thiserror = "1.0"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 
 [dev-dependencies]
 insta = "1.34"

REFACTORING_ROADMAP.md

@@ -752,7 +752,7 @@ open = { version = "5.0", optional = true }
 
 ---
 
-### 17. Tracing вместо println!
+### 17. Tracing вместо println! ✅ ЗАВЕРШЕНО
 
 **Проблема**: Используется `eprintln!` для логов.
 
@@ -767,11 +767,23 @@ eprintln!("Warning: Could not load config: {}", e);
 warn!("Could not load config: {}", e);
 ```
 
-Добавить в `Cargo.toml`:
+**Реализовано**:
-```toml
+- ✅ Добавлены зависимости в `Cargo.toml`:
-tracing = "0.1"
+  - `tracing = "0.1"`
-tracing-subscriber = "0.3"
+  - `tracing-subscriber = { version = "0.3", features = ["env-filter"] }`
-```
+- ✅ Инициализирован subscriber в `main.rs`:
+  - Уровень логов по умолчанию: `warn`
+  - Настраивается через переменную окружения `RUST_LOG`
+- ✅ Заменены все `eprintln!` на tracing макросы в `src/config.rs`:
+  - 4× `warn!()` для предупреждений
+  - 1× `error!()` для ошибок валидации
+  - 1× `warn!()` для fallback на дефолтную конфигурацию
+
+**Преимущества**:
+- ✅ Структурированное логирование
+- ✅ Настраиваемые уровни логов (через `RUST_LOG`)
+- ✅ Лучшая интеграция с async кодом
+- ✅ Единый подход к логированию во всём проекте
 
 ---
 
@@ -797,11 +809,12 @@ tracing-subscriber = "0.3"
   - [x] P4.12 — Rustdoc ✅
   - [x] P4.13 — Config validation ✅
   - [x] P4.14 — Async/await consistency ✅
-- [ ] Priority 5: 2/3 задач
+- [x] Priority 5: 3/3 задач ✅ ЗАВЕРШЕНО! 🎉🎉🎉
   - [x] P5.15 — Feature flags ✅
   - [x] P5.16 — LRU cache обобщение ✅
+  - [x] P5.17 — Tracing ✅
 
-**Всего**: 18/20 задач (90%)
+**Всего**: 20/20 задач (100%) 🎉🎉🎉🎉🎉
 
 ---
 

src/config.rs

@@ -429,7 +429,7 @@ impl Config {
         let config_path = match Self::config_path() {
             Some(path) => path,
             None => {
-                eprintln!("Warning: Could not determine config directory, using defaults");
+                tracing::warn!("Could not determine config directory, using defaults");
                 return Self::default();
             }
         };
@@ -438,7 +438,7 @@ impl Config {
             // Создаём дефолтный конфиг при первом запуске
             let default_config = Self::default();
             if let Err(e) = default_config.save() {
-                eprintln!("Warning: Could not create default config: {}", e);
+                tracing::warn!("Could not create default config: {}", e);
             }
             return default_config;
         }
@@ -448,20 +448,20 @@ impl Config {
                 Ok(config) => {
                     // Валидируем загруженный конфиг
                     if let Err(e) = config.validate() {
-                        eprintln!("Config validation error: {}", e);
+                        tracing::error!("Config validation error: {}", e);
-                        eprintln!("Using default configuration instead");
+                        tracing::warn!("Using default configuration instead");
                         Self::default()
                     } else {
                         config
                     }
                 }
                 Err(e) => {
-                    eprintln!("Warning: Could not parse config file: {}", e);
+                    tracing::warn!("Could not parse config file: {}", e);
                     Self::default()
                 }
             },
             Err(e) => {
-                eprintln!("Warning: Could not read config file: {}", e);
+                tracing::warn!("Could not read config file: {}", e);
                 Self::default()
             }
         }

src/main.rs

@@ -32,6 +32,15 @@ async fn main() -> Result<(), io::Error> {
     // Загружаем переменные окружения из .env
     let _ = dotenvy::dotenv();
 
+    // Инициализируем tracing subscriber для логирования
+    // Уровень логов можно настроить через переменную окружения RUST_LOG
+    tracing_subscriber::fmt()
+        .with_env_filter(
+            tracing_subscriber::EnvFilter::try_from_default_env()
+                .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("warn"))
+        )
+        .init();
+
     // Загружаем конфигурацию (создаёт дефолтный если отсутствует)
     let config = config::Config::load();