Implement prefix-optional ID parsing (bd-170)

- Add internal/utils/id_parser.go with ParseIssueID and ResolvePartialID
- Update all CLI commands to accept IDs without prefix (e.g., '170' or 'bd-170')
- Add comprehensive tests for ID parsing functionality
- Works in direct mode; RPC handlers to be updated in bd-177

Commands updated:
- show, update, edit, close (show.go)
- reopen (reopen.go)
- dep add/remove/tree (dep.go)
- label add/remove/list (label.go)
- comments (comments.go)

Amp-Thread-ID: https://ampcode.com/threads/T-1f6a301b-b53f-440f-bd79-e453234ac1c9
Co-authored-by: Amp <amp@ampcode.com>

internal/utils/id_parser.go

@@ -0,0 +1,95 @@
+// Package utils provides utility functions for issue ID parsing and resolution.
+package utils
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/steveyegge/beads/internal/storage"
+	"github.com/steveyegge/beads/internal/types"
+)
+
+// ParseIssueID ensures an issue ID has the configured prefix.
+// If the input already has the prefix (e.g., "bd-a3f8e9"), returns it as-is.
+// If the input lacks the prefix (e.g., "a3f8e9"), adds the configured prefix.
+// Works with hierarchical IDs too: "a3f8e9.1.2" → "bd-a3f8e9.1.2"
+func ParseIssueID(input string, prefix string) string {
+	if prefix == "" {
+		prefix = "bd-"
+	}
+	
+	if strings.HasPrefix(input, prefix) {
+		return input
+	}
+	
+	return prefix + input
+}
+
+// ResolvePartialID resolves a potentially partial issue ID to a full ID.
+// Supports:
+// - Full IDs: "bd-a3f8e9" or "a3f8e9" → "bd-a3f8e9"
+// - Partial IDs: "a3f8" → "bd-a3f8e9" (if unique match, requires hash IDs)
+// - Hierarchical: "a3f8e9.1" → "bd-a3f8e9.1"
+//
+// Returns an error if:
+// - No issue found matching the ID
+// - Multiple issues match (ambiguous prefix)
+//
+// Note: Partial ID matching (shorter prefixes) requires hash-based IDs (bd-165).
+// For now, this primarily handles prefix-optional input (bd-a3f8e9 vs a3f8e9).
+func ResolvePartialID(ctx context.Context, store storage.Storage, input string) (string, error) {
+	// Get the configured prefix
+	prefix, err := store.GetConfig(ctx, "issue_prefix")
+	if err != nil || prefix == "" {
+		prefix = "bd-"
+	}
+	
+	// Ensure the input has the prefix
+	parsedID := ParseIssueID(input, prefix)
+	
+	// First try exact match
+	_, err = store.GetIssue(ctx, parsedID)
+	if err == nil {
+		return parsedID, nil
+	}
+	
+	// If exact match failed, try prefix search
+	filter := types.IssueFilter{}
+	
+	issues, err := store.SearchIssues(ctx, "", filter)
+	if err != nil {
+		return "", fmt.Errorf("failed to search issues: %w", err)
+	}
+	
+	var matches []string
+	for _, issue := range issues {
+		if strings.HasPrefix(issue.ID, parsedID) {
+			matches = append(matches, issue.ID)
+		}
+	}
+	
+	if len(matches) == 0 {
+		return "", fmt.Errorf("no issue found matching %q", input)
+	}
+	
+	if len(matches) > 1 {
+		return "", fmt.Errorf("ambiguous ID %q matches %d issues: %v\nUse more characters to disambiguate", input, len(matches), matches)
+	}
+	
+	return matches[0], nil
+}
+
+// ResolvePartialIDs resolves multiple potentially partial issue IDs.
+// Returns the resolved IDs and any errors encountered.
+func ResolvePartialIDs(ctx context.Context, store storage.Storage, inputs []string) ([]string, error) {
+	var resolved []string
+	for _, input := range inputs {
+		fullID, err := ResolvePartialID(ctx, store, input)
+		if err != nil {
+			return nil, err
+		}
+		resolved = append(resolved, fullID)
+	}
+	return resolved, nil
+}