Jarl 0.1.0: manage BIND through a web UI, REST API and CLI

Jarl keeps a BIND 9.20 server's whole configuration (views, ACLs, TSIG
keys, zones of every type, records, named.conf options) in SQLite and
renders named.conf, keys.conf and zone files from it.

Every change goes through one changeset pipeline: whole-configuration
validation, named-checkconf -z and named-checkzone in a staging
directory, atomic install, rndc reconfig/reload, serial verification
with rndc zonestatus, and rollback if named does not load the change.
Changes apply one at a time by default or are bundled and applied
together. Applied changesets can be reverted.

- jarld: the daemon with the REST API and an embedded web UI, plus import,
  adopt, check, resync, backup and local user recovery commands
- jarl: the CLI, including ACME DNS-01 hooks for certbot and acme.sh
- users with argon2id passwords and CSRF-protected sessions; hashed API
  tokens with granular grants and roles; an audit log
- systemd unit, sysusers.d/tmpfiles.d files, Makefile
- unit tests, integration tests against a real named, scripts/e2e.sh
- docs/ guides, README and CHANGELOG

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/engine/errors.go

@@ -0,0 +1,61 @@
+package engine
+
+import (
+	"errors"
+	"fmt"
+
+	"jarl/internal/bind"
+	"jarl/internal/validate"
+)
+
+// ErrorKind classifies engine errors (the API maps them to HTTP status
+// codes).
+type ErrorKind string
+
+const (
+	KindBadRequest ErrorKind = "bad_request"       // malformed or invalid input
+	KindForbidden  ErrorKind = "forbidden"         // permission denied
+	KindNotFound   ErrorKind = "not_found"         // object does not exist
+	KindConflict   ErrorKind = "conflict"          // concurrent change, wrong state
+	KindValidation ErrorKind = "validation_failed" // the resulting config has errors
+	KindBIND       ErrorKind = "bind_failed"       // named-checkconf or rndc failed
+	KindDrift      ErrorKind = "drift"             // files were changed outside Jarl
+	KindNotAdopted ErrorKind = "not_adopted"       // named does not load Jarl's config yet
+)
+
+// Error is an engine error with details for the caller.
+type Error struct {
+	Kind     ErrorKind          `json:"code"`
+	Message  string             `json:"message"`
+	OpSeq    int                `json:"op,omitempty"` // the operation that failed
+	Problems []validate.Problem `json:"problems,omitempty"`
+	Check    []CheckMessage     `json:"check,omitempty"`
+	Diff     string             `json:"diff,omitempty"`
+}
+
+func (e *Error) Error() string {
+	if e.OpSeq > 0 {
+		return fmt.Sprintf("operation %d: %s", e.OpSeq, e.Message)
+	}
+	return e.Message
+}
+
+func errf(kind ErrorKind, format string, args ...any) *Error {
+	return &Error{Kind: kind, Message: fmt.Sprintf(format, args...)}
+}
+
+// AsError returns err as *Error, if it is one.
+func AsError(err error) (*Error, bool) {
+	var e *Error
+	ok := errors.As(err, &e)
+	return e, ok
+}
+
+// CheckMessage is a named-checkconf message mapped back to the Jarl object
+// that produced the offending line.
+type CheckMessage struct {
+	bind.Message
+	ObjectType string `json:"object_type,omitempty"`
+	ObjectID   int64  `json:"object_id,omitempty"`
+	Object     string `json:"object,omitempty"`
+}