Report or refuse each unusable file webhooker reads (closes #290)

An audit of every file webhooker reads configuration or required state from found cases that carried on silently. A zero-length webhooker.db, and a missing or zero-length per-webhook database, now log the "created a new, empty database" warning naming the file; restart recovery opens every live webhook's database, checking under the manager's lock that it still exists, so a missing one is reported at start. The main database's open errors name webhooker.db, for the server and webhooker resetpw; resetpw refuses a zero-length webhooker.db. A directory in place of any database file or its -wal or -shm is refused naming it. The README says how each case is treated. Also closes #459.

Model: opus-5-5

internal/database/database.go

@@ -8,7 +8,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/fs"
 	"log/slog"
 	"os"
 	"path/filepath"
@@ -203,8 +202,7 @@ func (d *Database) connectTo(dataDir string) error {
 	// Checked before opening, which creates the file. A DATA_DIR that
 	// is unexpectedly empty -- its volume not mounted, say -- looks
 	// exactly like a first start, so a new database is a warning.
-	_, statErr := os.Stat(dbPath)
-	created := errors.Is(statErr, fs.ErrNotExist)
+	created := missingOrEmpty(dbPath)
 
 	// Opened through OpenSQLite so this handle carries the same WAL
 	// journaling, busy timeout, immediate-transaction locking, and pool
@@ -213,13 +211,15 @@ func (d *Database) connectTo(dataDir string) error {
 	if err != nil {
 		d.log.Error(
 			"failed to open database",
+			"path", dbPath,
 			"error", err,
 		)
 
 		return err
 	}
 
-	// Then use it with GORM
+	// Then use it with GORM. Its errors are SQLite's alone and name no
+	// file, so the path is added to them here.
 	db, err := gorm.Open(sqlite.Dialector{
 		Conn: sqlDB,
 	}, &gorm.Config{
@@ -229,10 +229,11 @@ func (d *Database) connectTo(dataDir string) error {
 	if err != nil {
 		d.log.Error(
 			"failed to connect to database",
+			"path", dbPath,
 			"error", err,
 		)
 
-		return err
+		return fmt.Errorf("connecting to %s: %w", dbPath, err)
 	}
 
 	d.db = db
@@ -243,8 +244,12 @@ func (d *Database) connectTo(dataDir string) error {
 		d.log.Info("connected to database", "path", dbPath)
 	}
 
-	// Run migrations
-	return d.migrate()
+	err = d.migrate()
+	if err != nil {
+		return fmt.Errorf("migrating %s: %w", dbPath, err)
+	}
+
+	return nil
 }
 
 func (d *Database) migrate() error {