fix: Post-PR #8 critical improvements (bd-64, bd-65, bd-66, bd-67)

This commit addresses all critical follow-up issues identified in the
code review of PR #8 (atomic counter implementation).

## bd-64: Fix SyncAllCounters performance bottleneck (P0)
- Replace SyncAllCounters() on every CreateIssue with lazy initialization
- Add ensureCounterInitialized() that only scans prefix-specific issues on first use
- Performance improvement: O(n) full table scan → O(1) for subsequent creates
- Add comprehensive tests in lazy_init_test.go

## bd-65: Add migration for issue_counters table (P1)
- Add migrateIssueCountersTable() similar to migrateDirtyIssuesTable()
- Checks if table is empty and syncs from existing issues on first open
- Handles both fresh databases and migrations from old databases
- Add comprehensive tests in migration_test.go (3 scenarios)

## bd-66: Make import counter sync failure fatal (P1)
- Change SyncAllCounters() failure from warning to fatal error in import
- Prevents ID collisions when counter sync fails
- Data integrity > convenience

## bd-67: Update test comments (P2)
- Update TestMultiProcessIDGeneration comments to reflect fix is in place
- Change "With the bug, we expect errors" → "After the fix, all should succeed"

All tests pass. Atomic counter implementation is now production-ready.

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

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

internal/storage/sqlite/lazy_init_test.go

@@ -0,0 +1,217 @@
+package sqlite
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/steveyegge/beads/internal/types"
+)
+
+// TestLazyCounterInitialization verifies that counters are initialized lazily
+// on first use, not by scanning the entire database on every CreateIssue
+func TestLazyCounterInitialization(t *testing.T) {
+	// Create temporary directory
+	tmpDir, err := os.MkdirTemp("", "beads-lazy-init-test-*")
+	if err != nil {
+		t.Fatalf("failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	dbPath := filepath.Join(tmpDir, "test.db")
+
+	// Initialize database
+	store, err := New(dbPath)
+	if err != nil {
+		t.Fatalf("failed to create storage: %v", err)
+	}
+	defer store.Close()
+
+	ctx := context.Background()
+
+	// Create some issues with explicit IDs (simulating import)
+	existingIssues := []string{"bd-5", "bd-10", "bd-15"}
+	for _, id := range existingIssues {
+		issue := &types.Issue{
+			ID:        id,
+			Title:     "Existing issue",
+			Status:    types.StatusOpen,
+			Priority:  2,
+			IssueType: types.TypeTask,
+		}
+		err := store.CreateIssue(ctx, issue, "test-user")
+		if err != nil {
+			t.Fatalf("CreateIssue with explicit ID failed: %v", err)
+		}
+	}
+
+	// Verify no counter exists yet (lazy init hasn't happened)
+	var count int
+	err = store.db.QueryRow(`SELECT COUNT(*) FROM issue_counters WHERE prefix = 'bd'`).Scan(&count)
+	if err != nil {
+		t.Fatalf("Failed to query counters: %v", err)
+	}
+
+	if count != 0 {
+		t.Errorf("Expected no counter yet, but found %d", count)
+	}
+
+	// Now create an issue with auto-generated ID
+	// This should trigger lazy initialization
+	autoIssue := &types.Issue{
+		Title:     "Auto-generated ID",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+
+	err = store.CreateIssue(ctx, autoIssue, "test-user")
+	if err != nil {
+		t.Fatalf("CreateIssue with auto ID failed: %v", err)
+	}
+
+	// Verify the ID is correct (should be bd-16, after bd-15)
+	if autoIssue.ID != "bd-16" {
+		t.Errorf("Expected bd-16, got %s", autoIssue.ID)
+	}
+
+	// Verify counter was initialized
+	var lastID int
+	err = store.db.QueryRow(`SELECT last_id FROM issue_counters WHERE prefix = 'bd'`).Scan(&lastID)
+	if err != nil {
+		t.Fatalf("Failed to query counter: %v", err)
+	}
+
+	if lastID != 16 {
+		t.Errorf("Expected counter at 16, got %d", lastID)
+	}
+
+	// Create another issue - should NOT re-scan, just increment
+	anotherIssue := &types.Issue{
+		Title:     "Another auto-generated ID",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+
+	err = store.CreateIssue(ctx, anotherIssue, "test-user")
+	if err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+
+	if anotherIssue.ID != "bd-17" {
+		t.Errorf("Expected bd-17, got %s", anotherIssue.ID)
+	}
+}
+
+// TestLazyCounterInitializationMultiplePrefix tests lazy init with multiple prefixes
+func TestLazyCounterInitializationMultiplePrefix(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	// Set a custom prefix
+	err := store.SetConfig(ctx, "issue_prefix", "custom")
+	if err != nil {
+		t.Fatalf("SetConfig failed: %v", err)
+	}
+
+	// Create issue with default prefix first
+	err = store.SetConfig(ctx, "issue_prefix", "bd")
+	if err != nil {
+		t.Fatalf("SetConfig failed: %v", err)
+	}
+
+	bdIssue := &types.Issue{
+		Title:     "BD issue",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+
+	err = store.CreateIssue(ctx, bdIssue, "test-user")
+	if err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+
+	if bdIssue.ID != "bd-1" {
+		t.Errorf("Expected bd-1, got %s", bdIssue.ID)
+	}
+
+	// Now switch to custom prefix
+	err = store.SetConfig(ctx, "issue_prefix", "custom")
+	if err != nil {
+		t.Fatalf("SetConfig failed: %v", err)
+	}
+
+	customIssue := &types.Issue{
+		Title:     "Custom issue",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+
+	err = store.CreateIssue(ctx, customIssue, "test-user")
+	if err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+
+	if customIssue.ID != "custom-1" {
+		t.Errorf("Expected custom-1, got %s", customIssue.ID)
+	}
+
+	// Verify both counters exist
+	var count int
+	err = store.db.QueryRow(`SELECT COUNT(*) FROM issue_counters`).Scan(&count)
+	if err != nil {
+		t.Fatalf("Failed to query counters: %v", err)
+	}
+
+	if count != 2 {
+		t.Errorf("Expected 2 counters, got %d", count)
+	}
+}
+
+// TestCounterInitializationFromExisting tests that the counter
+// correctly initializes from the max ID of existing issues
+func TestCounterInitializationFromExisting(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	// Create issues with explicit IDs, out of order
+	explicitIDs := []string{"bd-5", "bd-100", "bd-42", "bd-7"}
+	for _, id := range explicitIDs {
+		issue := &types.Issue{
+			ID:        id,
+			Title:     "Explicit ID",
+			Status:    types.StatusOpen,
+			Priority:  2,
+			IssueType: types.TypeTask,
+		}
+		err := store.CreateIssue(ctx, issue, "test-user")
+		if err != nil {
+			t.Fatalf("CreateIssue failed: %v", err)
+		}
+	}
+
+	// Now auto-generate - should start at 101 (max is bd-100)
+	autoIssue := &types.Issue{
+		Title:     "Auto ID",
+		Status:    types.StatusOpen,
+		Priority:  2,
+		IssueType: types.TypeTask,
+	}
+
+	err := store.CreateIssue(ctx, autoIssue, "test-user")
+	if err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+
+	if autoIssue.ID != "bd-101" {
+		t.Errorf("Expected bd-101 (max was bd-100), got %s", autoIssue.ID)
+	}
+}