Implement local SQLite index database with repositories

- Add SQLite database connection management with proper error handling
- Implement schema for files, chunks, blobs, and snapshots tables
- Create repository pattern for each database table
- Add transaction support with proper rollback handling
- Integrate database module with fx dependency injection
- Make index path configurable via VAULTIK_INDEX_PATH env var
- Add fatal error handling for database integrity issues
- Update DESIGN.md to clarify file_chunks vs chunk_files distinction
- Remove FinalHash from BlobInfo (blobs are content-addressable)
- Add file metadata support (mtime, ctime, mode, uid, gid, symlinks)

internal/database/chunk_files.go

@@ -0,0 +1,88 @@
+package database
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+type ChunkFileRepository struct {
+	db *DB
+}
+
+func NewChunkFileRepository(db *DB) *ChunkFileRepository {
+	return &ChunkFileRepository{db: db}
+}
+
+func (r *ChunkFileRepository) Create(ctx context.Context, tx *sql.Tx, cf *ChunkFile) error {
+	query := `
+		INSERT INTO chunk_files (chunk_hash, file_path, file_offset, length)
+		VALUES (?, ?, ?, ?)
+		ON CONFLICT(chunk_hash, file_path) DO NOTHING
+	`
+
+	var err error
+	if tx != nil {
+		_, err = tx.ExecContext(ctx, query, cf.ChunkHash, cf.FilePath, cf.FileOffset, cf.Length)
+	} else {
+		_, err = r.db.conn.ExecContext(ctx, query, cf.ChunkHash, cf.FilePath, cf.FileOffset, cf.Length)
+	}
+
+	if err != nil {
+		return fmt.Errorf("inserting chunk_file: %w", err)
+	}
+
+	return nil
+}
+
+func (r *ChunkFileRepository) GetByChunkHash(ctx context.Context, chunkHash string) ([]*ChunkFile, error) {
+	query := `
+		SELECT chunk_hash, file_path, file_offset, length
+		FROM chunk_files
+		WHERE chunk_hash = ?
+	`
+
+	rows, err := r.db.conn.QueryContext(ctx, query, chunkHash)
+	if err != nil {
+		return nil, fmt.Errorf("querying chunk files: %w", err)
+	}
+	defer CloseRows(rows)
+
+	var chunkFiles []*ChunkFile
+	for rows.Next() {
+		var cf ChunkFile
+		err := rows.Scan(&cf.ChunkHash, &cf.FilePath, &cf.FileOffset, &cf.Length)
+		if err != nil {
+			return nil, fmt.Errorf("scanning chunk file: %w", err)
+		}
+		chunkFiles = append(chunkFiles, &cf)
+	}
+
+	return chunkFiles, rows.Err()
+}
+
+func (r *ChunkFileRepository) GetByFilePath(ctx context.Context, filePath string) ([]*ChunkFile, error) {
+	query := `
+		SELECT chunk_hash, file_path, file_offset, length
+		FROM chunk_files
+		WHERE file_path = ?
+	`
+
+	rows, err := r.db.conn.QueryContext(ctx, query, filePath)
+	if err != nil {
+		return nil, fmt.Errorf("querying chunk files: %w", err)
+	}
+	defer CloseRows(rows)
+
+	var chunkFiles []*ChunkFile
+	for rows.Next() {
+		var cf ChunkFile
+		err := rows.Scan(&cf.ChunkHash, &cf.FilePath, &cf.FileOffset, &cf.Length)
+		if err != nil {
+			return nil, fmt.Errorf("scanning chunk file: %w", err)
+		}
+		chunkFiles = append(chunkFiles, &cf)
+	}
+
+	return chunkFiles, rows.Err()
+}