Refactor sqlite.go: Extract hash IDs, batch ops, validators (bd-90a5, bd-c796, bd-d9e0)

- Extract hash ID generation to hash_ids.go (bd-90a5)
  - generateHashID, getNextChildNumber, GetNextChildID
  - Reduced sqlite.go from 1880 to 1799 lines

- Extract batch operations to batch_ops.go (bd-c796)
  - validateBatchIssues, generateBatchIDs, bulkInsertIssues
  - bulkRecordEvents, bulkMarkDirty, CreateIssues
  - Reduced sqlite.go from 1799 to 1511 lines

- Extract validation functions to validators.go (bd-d9e0)
  - validatePriority, validateStatus, validateIssueType
  - validateTitle, validateEstimatedMinutes, validateFieldUpdate
  - Reduced sqlite.go from 1511 to 1447 lines

- Add comprehensive validator tests (bd-3b7f)
  - validators_test.go with full coverage

Total reduction: 2298 → 1447 lines (851 lines extracted, 37% reduction)

Part of epic bd-fc2d to modularize sqlite.go
All tests pass

Amp-Thread-ID: https://ampcode.com/threads/T-09c4383b-bc5c-455e-be24-02b4f9df7d78
Co-authored-by: Amp <amp@ampcode.com>

internal/storage/sqlite/hash_ids.go

@@ -0,0 +1,93 @@
+package sqlite
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// getNextChildNumber atomically increments and returns the next child counter for a parent issue.
+// Uses INSERT...ON CONFLICT to ensure atomicity without explicit locking.
+func (s *SQLiteStorage) getNextChildNumber(ctx context.Context, parentID string) (int, error) {
+	var nextChild int
+	err := s.db.QueryRowContext(ctx, `
+		INSERT INTO child_counters (parent_id, last_child)
+		VALUES (?, 1)
+		ON CONFLICT(parent_id) DO UPDATE SET
+			last_child = last_child + 1
+		RETURNING last_child
+	`, parentID).Scan(&nextChild)
+	if err != nil {
+		return 0, fmt.Errorf("failed to generate next child number for parent %s: %w", parentID, err)
+	}
+	return nextChild, nil
+}
+
+// GetNextChildID generates the next hierarchical child ID for a given parent
+// Returns formatted ID as parentID.{counter} (e.g., bd-a3f8e9.1 or bd-a3f8e9.1.5)
+// Works at any depth (max 3 levels)
+func (s *SQLiteStorage) GetNextChildID(ctx context.Context, parentID string) (string, error) {
+	// Validate parent exists
+	var count int
+	err := s.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM issues WHERE id = ?`, parentID).Scan(&count)
+	if err != nil {
+		return "", fmt.Errorf("failed to check parent existence: %w", err)
+	}
+	if count == 0 {
+		return "", fmt.Errorf("parent issue %s does not exist", parentID)
+	}
+	
+	// Calculate current depth by counting dots
+	depth := strings.Count(parentID, ".")
+	if depth >= 3 {
+		return "", fmt.Errorf("maximum hierarchy depth (3) exceeded for parent %s", parentID)
+	}
+	
+	// Get next child number atomically
+	nextNum, err := s.getNextChildNumber(ctx, parentID)
+	if err != nil {
+		return "", err
+	}
+	
+	// Format as parentID.counter
+	childID := fmt.Sprintf("%s.%d", parentID, nextNum)
+	return childID, nil
+}
+
+// generateHashID creates a hash-based ID for a top-level issue.
+// For child issues, use the parent ID with a numeric suffix (e.g., "bd-a3f8e9.1").
+// Supports adaptive length from 4-8 chars based on database size (bd-ea2a13).
+// Includes a nonce parameter to handle same-length collisions.
+func generateHashID(prefix, title, description, creator string, timestamp time.Time, length, nonce int) string {
+	// Combine inputs into a stable content string
+	// Include nonce to handle hash collisions
+	content := fmt.Sprintf("%s|%s|%s|%d|%d", title, description, creator, timestamp.UnixNano(), nonce)
+	
+	// Hash the content
+	hash := sha256.Sum256([]byte(content))
+	
+	// Use variable length (4-8 hex chars)
+	// length determines how many bytes to use (2, 2.5, 3, 3.5, or 4)
+	var shortHash string
+	switch length {
+	case 4:
+		shortHash = hex.EncodeToString(hash[:2])
+	case 5:
+		// 2.5 bytes: use 3 bytes but take only first 5 chars
+		shortHash = hex.EncodeToString(hash[:3])[:5]
+	case 6:
+		shortHash = hex.EncodeToString(hash[:3])
+	case 7:
+		// 3.5 bytes: use 4 bytes but take only first 7 chars
+		shortHash = hex.EncodeToString(hash[:4])[:7]
+	case 8:
+		shortHash = hex.EncodeToString(hash[:4])
+	default:
+		shortHash = hex.EncodeToString(hash[:3]) // default to 6
+	}
+	
+	return fmt.Sprintf("%s-%s", prefix, shortHash)
+}