Add CLAUDE.md for Claude Code guidance

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: benbjohnson

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build and Test Commands
+
+```bash
+# Run all tests
+go test -v ./...
+
+# Build the CLI tool
+go build ./cmd/ltx
+
+# Install the CLI tool
+go install ./cmd/ltx
+
+# Build with version info (for releases)
+go build -ldflags "-s -w -X 'main.Version=<tag>' -X 'main.Commit=<sha>'" -o dist/ltx ./cmd/ltx
+```
+
+## Architecture Overview
+
+LTX (Lite Transaction File) is a Go library and CLI for managing SQLite transactional data in an encrypted, compactable format. It stores SQLite page-level changes with checksums for replication and backup workflows.
+
+### File Format (Version 3)
+
+The LTX format has three sections:
+1. **Header** (100 bytes) - Transaction metadata, page size, TXID range, timestamps, checksums
+2. **Page Block** - LZ4-compressed page data with individual page headers
+3. **Trailer** (16 bytes) - Post-apply checksum and file integrity checksum
+
+### Core Components
+
+- **ltx.go** - Core types: `Header`, `PageHeader`, `Trailer`, `TXID`, `Checksum`, `Pos`
+- **encoder.go** - Encodes data into LTX format with LZ4 compression and rolling checksums
+- **decoder.go** - Decodes LTX files with checksum verification
+- **compactor.go** - Merges multiple LTX files into one compacted file
+- **checksum.go** - CRC-ISO-64 checksum utilities
+
+### CLI Commands (cmd/ltx/)
+
+| Command | Purpose |
+|---------|---------|
+| `ltx apply -db PATH FILES...` | Apply LTX files to SQLite database |
+| `ltx verify FILES...` | Verify LTX file integrity |
+| `ltx list [-tsv] FILES...` | Display metadata for LTX files |
+| `ltx dump PATH` | Dump all metadata and page info |
+| `ltx checksum DB_PATH` | Compute CRC-ISO-64 checksum of database |
+| `ltx encode-db DB OUTPUT.LTX` | Create LTX snapshot from database |
+
+### Key Types
+
+```go
+type Pos struct {           // Replication position
+    TXID              TXID
+    PostApplyChecksum Checksum
+}
+
+type TXID uint64            // Transaction ID
+type Checksum uint64        // CRC-ISO-64 checksum
+```
+
+### Testing Patterns
+
+- Use `FileSpec` helper for creating in-memory test fixtures
+- Round-trip tests: encode -> decode -> verify
+- Table-driven tests for type parsing/marshaling
+
+# Version Control
+
+Always create feature branches. Never commit to main. Never do anything 
+destructive without asking.