feat(completion): add dynamic shell completions for issue IDs (#935)

Add intelligent shell completions that query the database to provide
issue ID suggestions with titles for commands that take IDs as arguments.

Changes:
- Add issueIDCompletion function that queries storage for all issues
- Register completion for show, update, close, edit, defer, undefer, reopen
- Add comprehensive test suite with 3 test cases
- Completions display ID with title as description (ID\tTitle format)

The completion function opens the database (read-only) and filters issues
based on the partially typed prefix, providing a better UX for commands
that require issue IDs.

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

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

cmd/bd/completions.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/beads/internal/beads"
+	"github.com/steveyegge/beads/internal/storage/sqlite"
+	"github.com/steveyegge/beads/internal/types"
+)
+
+// issueIDCompletion provides shell completion for issue IDs by querying the storage
+// and returning a list of IDs with their titles as descriptions
+func issueIDCompletion(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+	// Initialize storage if not already initialized
+	ctx := context.Background()
+	if rootCtx != nil {
+		ctx = rootCtx
+	}
+
+	// Get database path - use same logic as in PersistentPreRun
+	currentDBPath := dbPath
+	if currentDBPath == "" {
+		// Try to find database path
+		foundDB := beads.FindDatabasePath()
+		if foundDB != "" {
+			currentDBPath = foundDB
+		} else {
+			// Default path
+			currentDBPath = filepath.Join(".beads", beads.CanonicalDatabaseName)
+		}
+	}
+
+	// Open database if store is not initialized
+	currentStore := store
+	if currentStore == nil {
+		var err error
+		timeout := 30 * time.Second
+		if lockTimeout > 0 {
+			timeout = lockTimeout
+		}
+		currentStore, err = sqlite.NewReadOnlyWithTimeout(ctx, currentDBPath, timeout)
+		if err != nil {
+			// If we can't open database, return empty completion
+			return nil, cobra.ShellCompDirectiveNoFileComp
+		}
+		defer currentStore.Close()
+	}
+
+	// Use SearchIssues with empty query and default filter to get all issues
+	filter := types.IssueFilter{}
+	issues, err := currentStore.SearchIssues(ctx, "", filter)
+	if err != nil {
+		// If we can't list issues, return empty completion
+		return nil, cobra.ShellCompDirectiveNoFileComp
+	}
+
+	// Build completion list
+	completions := make([]string, 0, len(issues))
+	for _, issue := range issues {
+		// Filter based on what's already typed
+		if toComplete != "" && !strings.HasPrefix(issue.ID, toComplete) {
+			continue
+		}
+
+		// Format: ID\tTitle (shown during completion)
+		completions = append(completions, fmt.Sprintf("%s\t%s", issue.ID, issue.Title))
+	}
+
+	return completions, cobra.ShellCompDirectiveNoFileComp
+}