Update AGENTS.md with detailed file structure

AGENTS.md

@@ -126,18 +126,54 @@ sc_decrypt(&ctx, ciphertext, ciphertext_len, plaintext, &plaintext_len);
 
 ### Directory Structure
 ```
-├── lib/                    # Core libraries (uasync, ll_queue, memory pools)
+├── lib/                    # Core libraries
 ├── src/                    # Main source code
-│   ├── utun.c             # Main program entry
-│   ├── etcp*.c            # ETCP protocol implementation
-│   ├── secure_channel.c   # Cryptography
-│   └── tun_if.c          # TUN/TAP interface
-├── tests/                 # Test programs
-├── doc/                   # Technical Specifications
-├── tinycrypt/             # TinyCrypt crypto library
-└── net_emulator/          # Network emulator
+├── tests/                  # Test programs
+├── doc/                    # Technical Specifications
+├── tinycrypt/              # TinyCrypt crypto library (external)
+└── net_emulator/           # Network emulator
 ```
 
+### File Overview
+
+**Core (src/)**
+- `utun.c` - Main program entry point, CLI parsing, daemon mode
+- `utun_instance.c/h` - Root instance lifecycle management
+- `tun_if.c/h` - Simplified TUN interface (init/write/close)
+
+**Network Stack (src/)**
+- `etcp.c/h` - ETCP protocol implementation (TCP-like with crypto)
+- `etcp_connections.c/h` - Socket and link management
+- `etcp_loadbalancer.c/h` - Multi-link load balancing
+- `pkt_normalizer.c/h` - Packet fragmentation/reassembly
+- `routing.c/h` - Routing table management
+
+**Crypto (src/)**
+- `secure_channel.c/h` - AES-CCM encryption with ECC key exchange
+- `crc32.c/h` - CRC32 checksums
+
+**Config (src/)**
+- `config_parser.c/h` - INI-style config file parsing
+- `config_updater.c/h` - Config file modification utilities
+
+**Libraries (lib/)**
+- `u_async.c/h` - Async event loop (epoll/poll, timers)
+- `ll_queue.c/h` - Lock-free linked list queue with callbacks
+- `memory_pool.c/h` - Fast object pool allocator
+- `debug_config.c/h` - Debug logging system
+- `timeout_heap.c/h` - Min-heap for timer management
+- `sha256.c/h` - SHA256 hashing
+
+**Tests (tests/)**
+- `test_etcp_*.c` - ETCP protocol tests
+- `test_crypto.c` - TinyCrypt AES/CCM tests
+- `test_ecc_encrypt.c` - ECC encryption tests
+- `test_ll_queue.c` - Queue functionality tests
+- `bench_*.c` - Performance benchmarks
+
+**External**
+- `tinycrypt/` - TinyCrypt library (AES, ECC, SHA256)
+
 ### Key Components
 - **UASYNC:** Asynchronous event loop for sockets and timers
 - **LL_QUEUE:** Lock-free lockstep queue for packet handling