feat(storage): add Dolt backend for version-controlled issue storage

Implements a complete Dolt storage backend that mirrors the SQLite implementation
with MySQL-compatible syntax and adds version control capabilities.

Key features:
- Full Storage interface implementation (~50 methods)
- Version control operations: commit, push, pull, branch, merge, checkout
- History queries via AS OF and dolt_history_* tables
- Cell-level merge instead of line-level JSONL merge
- SQL injection protection with input validation

Bug fixes applied during implementation:
- Added missing quality_score, work_type, source_system to scanIssue
- Fixed Status() to properly parse boolean staged column
- Added validation to CreateIssues (was missing in batch create)
- Made RenameDependencyPrefix transactional
- Expanded GetIssueHistory to return more complete data

Test coverage: 17 tests covering CRUD, dependencies, labels, search,
comments, events, statistics, and SQL injection protection.

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

internal/storage/dolt/events.go

@@ -0,0 +1,160 @@
+package dolt
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+
+	"github.com/steveyegge/beads/internal/types"
+)
+
+// AddComment adds a comment event to an issue
+func (s *DoltStore) AddComment(ctx context.Context, issueID, actor, comment string) error {
+	_, err := s.db.ExecContext(ctx, `
+		INSERT INTO events (issue_id, event_type, actor, comment)
+		VALUES (?, ?, ?, ?)
+	`, issueID, types.EventCommented, actor, comment)
+	if err != nil {
+		return fmt.Errorf("failed to add comment: %w", err)
+	}
+	return nil
+}
+
+// GetEvents retrieves events for an issue
+func (s *DoltStore) GetEvents(ctx context.Context, issueID string, limit int) ([]*types.Event, error) {
+	query := `
+		SELECT id, issue_id, event_type, actor, old_value, new_value, comment, created_at
+		FROM events
+		WHERE issue_id = ?
+		ORDER BY created_at DESC
+	`
+	args := []interface{}{issueID}
+
+	if limit > 0 {
+		query += fmt.Sprintf(" LIMIT %d", limit)
+	}
+
+	rows, err := s.db.QueryContext(ctx, query, args...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get events: %w", err)
+	}
+	defer rows.Close()
+
+	var events []*types.Event
+	for rows.Next() {
+		var event types.Event
+		var oldValue, newValue, comment sql.NullString
+		if err := rows.Scan(&event.ID, &event.IssueID, &event.EventType, &event.Actor,
+			&oldValue, &newValue, &comment, &event.CreatedAt); err != nil {
+			return nil, fmt.Errorf("failed to scan event: %w", err)
+		}
+		if oldValue.Valid {
+			event.OldValue = &oldValue.String
+		}
+		if newValue.Valid {
+			event.NewValue = &newValue.String
+		}
+		if comment.Valid {
+			event.Comment = &comment.String
+		}
+		events = append(events, &event)
+	}
+	return events, rows.Err()
+}
+
+// AddIssueComment adds a comment to an issue (structured comment)
+func (s *DoltStore) AddIssueComment(ctx context.Context, issueID, author, text string) (*types.Comment, error) {
+	result, err := s.db.ExecContext(ctx, `
+		INSERT INTO comments (issue_id, author, text, created_at)
+		VALUES (?, ?, ?, ?)
+	`, issueID, author, text, time.Now())
+	if err != nil {
+		return nil, fmt.Errorf("failed to add comment: %w", err)
+	}
+
+	id, err := result.LastInsertId()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get comment id: %w", err)
+	}
+
+	return &types.Comment{
+		ID:        id,
+		IssueID:   issueID,
+		Author:    author,
+		Text:      text,
+		CreatedAt: time.Now(),
+	}, nil
+}
+
+// GetIssueComments retrieves all comments for an issue
+func (s *DoltStore) GetIssueComments(ctx context.Context, issueID string) ([]*types.Comment, error) {
+	rows, err := s.db.QueryContext(ctx, `
+		SELECT id, issue_id, author, text, created_at
+		FROM comments
+		WHERE issue_id = ?
+		ORDER BY created_at ASC
+	`, issueID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get comments: %w", err)
+	}
+	defer rows.Close()
+
+	var comments []*types.Comment
+	for rows.Next() {
+		var c types.Comment
+		if err := rows.Scan(&c.ID, &c.IssueID, &c.Author, &c.Text, &c.CreatedAt); err != nil {
+			return nil, fmt.Errorf("failed to scan comment: %w", err)
+		}
+		comments = append(comments, &c)
+	}
+	return comments, rows.Err()
+}
+
+// GetCommentsForIssues retrieves comments for multiple issues
+func (s *DoltStore) GetCommentsForIssues(ctx context.Context, issueIDs []string) (map[string][]*types.Comment, error) {
+	if len(issueIDs) == 0 {
+		return make(map[string][]*types.Comment), nil
+	}
+
+	placeholders := make([]string, len(issueIDs))
+	args := make([]interface{}, len(issueIDs))
+	for i, id := range issueIDs {
+		placeholders[i] = "?"
+		args[i] = id
+	}
+
+	query := fmt.Sprintf(`
+		SELECT id, issue_id, author, text, created_at
+		FROM comments
+		WHERE issue_id IN (%s)
+		ORDER BY issue_id, created_at ASC
+	`, joinStrings(placeholders, ","))
+
+	rows, err := s.db.QueryContext(ctx, query, args...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get comments: %w", err)
+	}
+	defer rows.Close()
+
+	result := make(map[string][]*types.Comment)
+	for rows.Next() {
+		var c types.Comment
+		if err := rows.Scan(&c.ID, &c.IssueID, &c.Author, &c.Text, &c.CreatedAt); err != nil {
+			return nil, fmt.Errorf("failed to scan comment: %w", err)
+		}
+		result[c.IssueID] = append(result[c.IssueID], &c)
+	}
+	return result, rows.Err()
+}
+
+func joinStrings(strs []string, sep string) string {
+	if len(strs) == 0 {
+		return ""
+	}
+	result := strs[0]
+	for _, s := range strs[1:] {
+		result += sep + s
+	}
+	return result
+}