Add rename-prefix command (bd-420)

- Implement bd rename-prefix command with --dry-run and --json flags
- Add prefix validation (max 8 chars, lowercase, starts with letter)
- Update all issue IDs and text references atomically per issue
- Update dependencies, labels, events, and counters
- Fix counter merge to use MAX() to prevent ID collisions
- Update snapshot tables for FK integrity
- Add comprehensive tests for validation and rename workflow
- Document in README.md and AGENTS.md

Known limitation: Each issue updates in its own transaction.
A failure mid-way could leave mixed state. Acceptable for
intended use case (infrequent operation on small DBs).

Amp-Thread-ID: https://ampcode.com/threads/T-7e77b779-bd88-44f2-9f0b-a9f2ccd54d38
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/rename_prefix.go

@@ -0,0 +1,191 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"regexp"
+	"strings"
+
+	"github.com/fatih/color"
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/beads/internal/types"
+)
+
+var renamePrefixCmd = &cobra.Command{
+	Use:   "rename-prefix <new-prefix>",
+	Short: "Rename the issue prefix for all issues",
+	Long: `Rename the issue prefix for all issues in the database.
+This will update all issue IDs and all text references across all fields.
+
+Prefix validation rules:
+- Max length: 8 characters
+- Allowed characters: lowercase letters, numbers, hyphens
+- Must start with a letter
+- Must end with a hyphen (e.g., 'kw-', 'work-')
+- Cannot be empty or just a hyphen
+
+Example:
+  bd rename-prefix kw-         # Rename from 'knowledge-work-' to 'kw-'`,
+	Args: cobra.ExactArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		newPrefix := args[0]
+		dryRun, _ := cmd.Flags().GetBool("dry-run")
+
+		ctx := context.Background()
+
+		if err := validatePrefix(newPrefix); err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+
+		oldPrefix, err := store.GetConfig(ctx, "issue_prefix")
+		if err != nil || oldPrefix == "" {
+			fmt.Fprintf(os.Stderr, "Error: failed to get current prefix: %v\n", err)
+			os.Exit(1)
+		}
+
+		newPrefix = strings.TrimRight(newPrefix, "-")
+
+		if oldPrefix == newPrefix {
+			fmt.Fprintf(os.Stderr, "Error: new prefix is the same as current prefix: %s\n", oldPrefix)
+			os.Exit(1)
+		}
+
+		issues, err := store.SearchIssues(ctx, "", types.IssueFilter{})
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: failed to list issues: %v\n", err)
+			os.Exit(1)
+		}
+
+		if len(issues) == 0 {
+			fmt.Printf("No issues to rename. Updating prefix to %s\n", newPrefix)
+			if !dryRun {
+				if err := store.SetConfig(ctx, "issue_prefix", newPrefix); err != nil {
+					fmt.Fprintf(os.Stderr, "Error: failed to update prefix: %v\n", err)
+					os.Exit(1)
+				}
+			}
+			return
+		}
+
+		if dryRun {
+			cyan := color.New(color.FgCyan).SprintFunc()
+			fmt.Printf("DRY RUN: Would rename %d issues from prefix '%s' to '%s'\n\n", len(issues), oldPrefix, newPrefix)
+			fmt.Printf("Sample changes:\n")
+			for i, issue := range issues {
+				if i >= 5 {
+					fmt.Printf("... and %d more issues\n", len(issues)-5)
+					break
+				}
+				oldID := fmt.Sprintf("%s-%s", oldPrefix, strings.TrimPrefix(issue.ID, oldPrefix+"-"))
+				newID := fmt.Sprintf("%s-%s", newPrefix, strings.TrimPrefix(issue.ID, oldPrefix+"-"))
+				fmt.Printf("  %s -> %s\n", cyan(oldID), cyan(newID))
+			}
+			return
+		}
+
+		green := color.New(color.FgGreen).SprintFunc()
+		cyan := color.New(color.FgCyan).SprintFunc()
+
+		fmt.Printf("Renaming %d issues from prefix '%s' to '%s'...\n", len(issues), oldPrefix, newPrefix)
+
+		if err := renamePrefixInDB(ctx, oldPrefix, newPrefix, issues); err != nil {
+			fmt.Fprintf(os.Stderr, "Error: failed to rename prefix: %v\n", err)
+			os.Exit(1)
+		}
+
+		fmt.Printf("%s Successfully renamed prefix from %s to %s\n", green("✓"), cyan(oldPrefix), cyan(newPrefix))
+
+		if jsonOutput {
+			result := map[string]interface{}{
+				"old_prefix":   oldPrefix,
+				"new_prefix":   newPrefix,
+				"issues_count": len(issues),
+			}
+			enc := json.NewEncoder(os.Stdout)
+			enc.SetIndent("", "  ")
+			_ = enc.Encode(result)
+		}
+	},
+}
+
+func validatePrefix(prefix string) error {
+	prefix = strings.TrimRight(prefix, "-")
+
+	if prefix == "" {
+		return fmt.Errorf("prefix cannot be empty")
+	}
+
+	if len(prefix) > 8 {
+		return fmt.Errorf("prefix too long (max 8 characters): %s", prefix)
+	}
+
+	matched, _ := regexp.MatchString(`^[a-z][a-z0-9-]*$`, prefix)
+	if !matched {
+		return fmt.Errorf("prefix must start with a lowercase letter and contain only lowercase letters, numbers, and hyphens: %s", prefix)
+	}
+
+	if strings.HasPrefix(prefix, "-") || strings.HasSuffix(prefix, "--") {
+		return fmt.Errorf("prefix has invalid hyphen placement: %s", prefix)
+	}
+
+	return nil
+}
+
+func renamePrefixInDB(ctx context.Context, oldPrefix, newPrefix string, issues []*types.Issue) error {
+	// NOTE: Each issue is updated in its own transaction. A failure mid-way could leave
+	// the database in a mixed state with some issues renamed and others not.
+	// For production use, consider implementing a single atomic RenamePrefix() method
+	// in the storage layer that wraps all updates in one transaction.
+	
+	oldPrefixPattern := regexp.MustCompile(`\b` + regexp.QuoteMeta(oldPrefix) + `-(\d+)\b`)
+
+	replaceFunc := func(match string) string {
+		return strings.Replace(match, oldPrefix+"-", newPrefix+"-", 1)
+	}
+
+	for _, issue := range issues {
+		oldID := issue.ID
+		numPart := strings.TrimPrefix(oldID, oldPrefix+"-")
+		newID := fmt.Sprintf("%s-%s", newPrefix, numPart)
+
+		issue.ID = newID
+
+		issue.Title = oldPrefixPattern.ReplaceAllStringFunc(issue.Title, replaceFunc)
+		issue.Description = oldPrefixPattern.ReplaceAllStringFunc(issue.Description, replaceFunc)
+		if issue.Design != "" {
+			issue.Design = oldPrefixPattern.ReplaceAllStringFunc(issue.Design, replaceFunc)
+		}
+		if issue.AcceptanceCriteria != "" {
+			issue.AcceptanceCriteria = oldPrefixPattern.ReplaceAllStringFunc(issue.AcceptanceCriteria, replaceFunc)
+		}
+		if issue.Notes != "" {
+			issue.Notes = oldPrefixPattern.ReplaceAllStringFunc(issue.Notes, replaceFunc)
+		}
+
+		if err := store.UpdateIssueID(ctx, oldID, newID, issue, actor); err != nil {
+			return fmt.Errorf("failed to update issue %s: %w", oldID, err)
+		}
+	}
+
+	if err := store.RenameDependencyPrefix(ctx, oldPrefix, newPrefix); err != nil {
+		return fmt.Errorf("failed to update dependencies: %w", err)
+	}
+
+	if err := store.RenameCounterPrefix(ctx, oldPrefix, newPrefix); err != nil {
+		return fmt.Errorf("failed to update counter: %w", err)
+	}
+
+	if err := store.SetConfig(ctx, "issue_prefix", newPrefix); err != nil {
+		return fmt.Errorf("failed to update config: %w", err)
+	}
+
+	return nil
+}
+
+func init() {
+	renamePrefixCmd.Flags().Bool("dry-run", false, "Preview changes without applying them")
+	rootCmd.AddCommand(renamePrefixCmd)
+}