Move schema_migrations table creation into 000.sql with INTEGER version column (#172)

Closes #171

Refactors the migration system to follow the [pixa pattern](sneak/pixa#36):

## Changes

### New file: `internal/database/migrations/000.sql`
- Bootstrap migration that creates `schema_migrations` with `version INTEGER PRIMARY KEY`
- Self-contained: includes both `CREATE TABLE IF NOT EXISTS` and `INSERT OR IGNORE INTO schema_migrations (version) VALUES (0)`

### Refactored: `internal/database/migrations.go`
- **Go code no longer creates the migrations table inline** — it reads and executes `000.sql` as a bootstrap step before the normal migration loop
- **`ParseMigrationVersion(filename)`** — exported function that extracts integer version from filenames like `001_initial.sql` → `1`
- **`ApplyMigrations(ctx, db, log)`** — exported function for tests to apply schema without full fx lifecycle
- **`bootstrapMigrationsTable`** — checks if table exists; if missing, runs `000.sql`; if present, checks for legacy format
- **`convertLegacyMigrations`** — one-time conversion for existing databases that stored versions as TEXT filenames (e.g. `"001_initial.sql"`) to INTEGER versions (e.g. `1`)
- **Transaction-wrapped migration application** — each migration runs in a transaction for atomicity
- Sentinel error `ErrInvalidMigrationFilename` for static error wrapping

### New file: `internal/database/migrations_test.go`
- `TestParseMigrationVersion` — valid/invalid filename parsing
- `TestApplyMigrationsFreshDatabase` — verifies bootstrap creates table, all migrations apply, application tables exist
- `TestApplyMigrationsIdempotent` — double-apply is a no-op
- `TestApplyMigrationsLegacyConversion` — simulates old TEXT-based table with filename entries, verifies conversion to integer format

## Backward Compatibility

Existing databases with the old TEXT-based `schema_migrations` table are automatically converted on first run. The conversion:
1. Detects legacy entries (versions containing `_`)
2. Parses integer version from each legacy filename
3. Drops the old table
4. Creates the new INTEGER-based table via `000.sql`
5. Re-inserts all parsed integer versions

All existing migrations (001-007) continue to work unchanged.

Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: clawbot <clawbot@sneak.berlin>
Reviewed-on: #172
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/database/migrations.go

@@ -2,36 +2,74 @@ package database
 
 import (
 	"context"
+	"database/sql"
 	"embed"
+	"errors"
 	"fmt"
 	"io/fs"
+	"log/slog"
 	"sort"
+	"strconv"
 	"strings"
 )
 
 //go:embed migrations/*.sql
 var migrationsFS embed.FS
 
-func (d *Database) migrate(ctx context.Context) error {
-	// Create migrations table if not exists
-	_, err := d.database.ExecContext(ctx, `
-		CREATE TABLE IF NOT EXISTS schema_migrations (
-			version TEXT PRIMARY KEY,
-			applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
-		)
-	`)
-	if err != nil {
-		return fmt.Errorf("failed to create migrations table: %w", err)
+// bootstrapVersion is the migration that creates the schema_migrations
+// table itself. It is applied before the normal migration loop.
+const bootstrapVersion = 0
+
+// ErrInvalidMigrationFilename indicates a migration filename does not follow
+// the expected "<version>.sql" or "<version>_<description>.sql" pattern.
+var ErrInvalidMigrationFilename = errors.New("invalid migration filename")
+
+// ParseMigrationVersion extracts the numeric version prefix from a migration
+// filename. Filenames must follow the pattern "<version>.sql" or
+// "<version>_<description>.sql", where version is a zero-padded numeric
+// string (e.g. "001", "002"). Returns the version as an integer and an
+// error if the filename does not match the expected pattern.
+func ParseMigrationVersion(filename string) (int, error) {
+	name := strings.TrimSuffix(filename, ".sql")
+	if name == "" || name == filename {
+		return 0, fmt.Errorf("%w: %q has no .sql extension or is empty", ErrInvalidMigrationFilename, filename)
 	}
 
-	// Get list of migration files
+	// Split on underscore to separate version from description.
+	// If there's no underscore, the entire stem is the version.
+	versionStr, _, _ := strings.Cut(name, "_")
+
+	if versionStr == "" {
+		return 0, fmt.Errorf("%w: %q has empty version prefix", ErrInvalidMigrationFilename, filename)
+	}
+
+	// Validate the version is purely numeric.
+	for _, ch := range versionStr {
+		if ch < '0' || ch > '9' {
+			return 0, fmt.Errorf(
+				"%w: %q version %q contains non-numeric character %q",
+				ErrInvalidMigrationFilename, filename, versionStr, string(ch),
+			)
+		}
+	}
+
+	version, err := strconv.Atoi(versionStr)
+	if err != nil {
+		return 0, fmt.Errorf("%w: %q: %w", ErrInvalidMigrationFilename, filename, err)
+	}
+
+	return version, nil
+}
+
+// collectMigrations reads the embedded migrations directory and returns
+// migration filenames sorted lexicographically.
+func collectMigrations() ([]string, error) {
 	entries, err := fs.ReadDir(migrationsFS, "migrations")
 	if err != nil {
-		return fmt.Errorf("failed to read migrations directory: %w", err)
+		return nil, fmt.Errorf("failed to read migrations directory: %w", err)
 	}
 
-	// Sort migrations by name
-	migrations := make([]string, 0, len(entries))
+	var migrations []string
 
 	for _, entry := range entries {
 		if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".sql") {
@@ -41,54 +79,113 @@ func (d *Database) migrate(ctx context.Context) error {
 
 	sort.Strings(migrations)
 
-	// Apply each migration
-	for _, migration := range migrations {
-		applied, err := d.isMigrationApplied(ctx, migration)
-		if err != nil {
-			return fmt.Errorf("failed to check migration %s: %w", migration, err)
-		}
+	return migrations, nil
+}
 
-		if applied {
-			d.log.Debug("migration already applied", "migration", migration)
+// bootstrapMigrationsTable ensures the schema_migrations table exists by
+// applying 000_migration.sql if the table is missing.
+func bootstrapMigrationsTable(ctx context.Context, db *sql.DB, log *slog.Logger) error {
+	var tableExists int
 
-			continue
-		}
+	err := db.QueryRowContext(ctx,
+		"SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND name='schema_migrations'",
+	).Scan(&tableExists)
+	if err != nil {
+		return fmt.Errorf("failed to check for migrations table: %w", err)
+	}
 
-		err = d.applyMigration(ctx, migration)
-		if err != nil {
-			return fmt.Errorf("failed to apply migration %s: %w", migration, err)
-		}
-
-		d.log.Info("migration applied", "migration", migration)
+	if tableExists == 0 {
+		return applyBootstrapMigration(ctx, db, log)
 	}
 
 	return nil
 }
 
-func (d *Database) isMigrationApplied(ctx context.Context, version string) (bool, error) {
-	var count int
-
-	err := d.database.QueryRowContext(
-		ctx,
-		"SELECT COUNT(*) FROM schema_migrations WHERE version = ?",
-		version,
-	).Scan(&count)
+// applyBootstrapMigration reads and executes 000_migration.sql to create the
+// schema_migrations table on a fresh database.
+func applyBootstrapMigration(ctx context.Context, db *sql.DB, log *slog.Logger) error {
+	content, err := migrationsFS.ReadFile("migrations/000_migration.sql")
 	if err != nil {
-		return false, fmt.Errorf("failed to query migration status: %w", err)
+		return fmt.Errorf("failed to read bootstrap migration 000_migration.sql: %w", err)
 	}
 
-	return count > 0, nil
+	if log != nil {
+		log.Info("applying bootstrap migration", "version", bootstrapVersion)
+	}
+
+	_, err = db.ExecContext(ctx, string(content))
+	if err != nil {
+		return fmt.Errorf("failed to apply bootstrap migration: %w", err)
+	}
+
+	return nil
 }
 
-func (d *Database) applyMigration(ctx context.Context, filename string) error {
-	content, err := migrationsFS.ReadFile("migrations/" + filename)
-	if err != nil {
-		return fmt.Errorf("failed to read migration file: %w", err)
+// ApplyMigrations applies all pending migrations to db. An optional logger
+// may be provided for informational output; pass nil for silent operation.
+// This is exported so tests can apply the real schema without the full fx
+// lifecycle.
+func ApplyMigrations(ctx context.Context, db *sql.DB, log *slog.Logger) error {
+	bootstrapErr := bootstrapMigrationsTable(ctx, db, log)
+	if bootstrapErr != nil {
+		return bootstrapErr
 	}
 
-	transaction, err := d.database.BeginTx(ctx, nil)
+	migrations, err := collectMigrations()
 	if err != nil {
-		return fmt.Errorf("failed to begin transaction: %w", err)
+		return err
+	}
+
+	for _, migration := range migrations {
+		version, parseErr := ParseMigrationVersion(migration)
+		if parseErr != nil {
+			return parseErr
+		}
+
+		// Check if already applied.
+		var count int
+
+		err = db.QueryRowContext(ctx,
+			"SELECT COUNT(*) FROM schema_migrations WHERE version = ?",
+			version,
+		).Scan(&count)
+		if err != nil {
+			return fmt.Errorf("failed to check migration %s: %w", migration, err)
+		}
+
+		if count > 0 {
+			if log != nil {
+				log.Debug("migration already applied", "version", version)
+			}
+
+			continue
+		}
+
+		// Apply migration in a transaction.
+		applyErr := applyMigrationTx(ctx, db, migration, version)
+		if applyErr != nil {
+			return applyErr
+		}
+
+		if log != nil {
+			log.Info("migration applied", "version", version)
+		}
+	}
+
+	return nil
+}
+
+// applyMigrationTx reads and executes a migration file within a transaction,
+// recording the version in schema_migrations on success.
+func applyMigrationTx(ctx context.Context, db *sql.DB, filename string, version int) error {
+	content, err := migrationsFS.ReadFile("migrations/" + filename)
+	if err != nil {
+		return fmt.Errorf("failed to read migration %s: %w", filename, err)
+	}
+
+	transaction, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		return fmt.Errorf("failed to begin transaction for migration %s: %w", filename, err)
 	}
 
 	defer func() {
@@ -97,26 +194,27 @@ func (d *Database) applyMigration(ctx context.Context, filename string) error {
 		}
 	}()
 
-	// Execute migration
 	_, err = transaction.ExecContext(ctx, string(content))
 	if err != nil {
-		return fmt.Errorf("failed to execute migration: %w", err)
+		return fmt.Errorf("failed to execute migration %s: %w", filename, err)
 	}
 
-	// Record migration
-	_, err = transaction.ExecContext(
-		ctx,
+	_, err = transaction.ExecContext(ctx,
 		"INSERT INTO schema_migrations (version) VALUES (?)",
-		filename,
+		version,
 	)
 	if err != nil {
-		return fmt.Errorf("failed to record migration: %w", err)
+		return fmt.Errorf("failed to record migration %s: %w", filename, err)
 	}
 
 	err = transaction.Commit()
 	if err != nil {
-		return fmt.Errorf("failed to commit migration: %w", err)
+		return fmt.Errorf("failed to commit migration %s: %w", filename, err)
 	}
 
 	return nil
 }
+
+func (d *Database) migrate(ctx context.Context) error {
+	return ApplyMigrations(ctx, d.database, d.log)
+}