Add TODO.md for unwrapped c api components

Author: stringintech

TODO.md

@@ -0,0 +1,64 @@
+# Bitcoin Kernel Go Wrapper - TODO
+
+This document lists the remaining C API functions and data structures from `bitcoinkernel.h` that haven't been wrapped yet in the Go kernel package.
+
+## Current Status
+
+✅ **Implemented:**
+- Chain parameters and context management
+- Block and block index operations
+- Chainstate manager functionality
+- Basic logging support
+
+❌ **Missing:**
+- Transaction processing pipeline
+- Script validation system
+- Block undo data handling
+- Complete callback system integration
+
+## Missing Data Structures
+
+### Core Transaction Types
+- **`kernel_Transaction`** - Transaction handling
+- **`kernel_ScriptPubkey`** - Script public key operations  
+- **`kernel_TransactionOutput`** - Transaction output operations
+- **`kernel_BlockPointer`** - Non-owned block pointers (from callbacks)
+- **`kernel_BlockUndo`** - Block undo data operations
+- **`kernel_ByteArray`** - Helper for serialized data
+
+## Missing Functions by Category
+
+### Transaction Operations
+- [ ] `kernel_transaction_create()` - Create transaction from serialized data
+- [ ] `kernel_transaction_destroy()` - Cleanup transaction
+
+### Script Operations
+- [ ] `kernel_script_pubkey_create()` - Create script pubkey
+- [ ] `kernel_script_pubkey_destroy()` - Cleanup script pubkey  
+- [ ] `kernel_copy_script_pubkey_data()` - Get serialized script data
+- [ ] `kernel_verify_script()` - **Script verification (IMPORTANT!)**
+
+### Transaction Output Operations
+- [ ] `kernel_transaction_output_create()` - Create transaction output
+- [ ] `kernel_transaction_output_destroy()` - Cleanup transaction output
+- [ ] `kernel_copy_script_pubkey_from_output()` - Extract script from output
+- [ ] `kernel_get_transaction_output_amount()` - Get output amount
+
+### Block Operations (Additional)
+- [ ] `kernel_block_pointer_get_hash()` - Get hash from block pointer
+- [ ] `kernel_copy_block_pointer_data()` - Copy data from block pointer  
+
+### Block Undo Operations
+- [ ] `kernel_read_block_undo_from_disk()` - Read undo data from disk
+- [ ] `kernel_block_undo_size()` - Get number of transactions in undo data
+- [ ] `kernel_get_transaction_undo_size()` - Get output count per transaction
+- [ ] `kernel_get_undo_output_height_by_index()` - Get output block height
+- [ ] `kernel_get_undo_output_by_index()` - Get specific undo output
+- [ ] `kernel_block_undo_destroy()` - Cleanup undo data
+
+### Utility Operations
+- [ ] `kernel_byte_array_destroy()` - Cleanup byte arrays
+
+### Callback Support
+- [ ] **Notification callbacks** - Full integration of kernel notification system
+- [ ] **Validation interface callbacks** - Block validation event handling