release: 0.1.0: Phases 0-11: panel, Postfix/DKIM, milter, backup, Docker image

Initial feature-complete implementation of the v1.0 specification (phases 0-11 of `docs/implementation-plan.md`).
Added:
  - Panel (Go, single static binary) with SQLite persistence, one-time
  - Domain management with per-domain DKIM (RSA-2048, generated in pure Go) and
  - Application (sender identity) management: SASL credentials via `sasldb2`,
  - Full Postfix relay config generated from env at container start: SMTPS 465,
  - Journal milter (pure Go, `go-milter`) recording every send to `send_log`;
  … (6 more in CHANGELOG)

Full detail: CHANGELOG.md (0.1.0).

internal/health/health.go

@@ -0,0 +1,53 @@
+// Package health reports the running container's own operating state for the
+// panel's status screen: the supervised processes, the TLS certificate Postfix
+// serves, and the milter sockets delivery depends on.
+//
+// Every check is read-only and reports a problem as a Status value rather than
+// an error return, so one broken component degrades a single line of the status
+// page instead of blanking the whole thing. The package also owns the Status
+// vocabulary shared with internal/dnscheck, so the panel renders every check —
+// local or DNS — through one set of badges.
+package health
+
+// Status is the outcome of a single check, in the order the status page treats
+// them: unknown < ok < warn < error, worst wins for a group.
+type Status string
+
+const (
+	// StatusUnknown means the check could not be performed at all (a missing
+	// setting, an unreachable resolver) — not evidence of a problem.
+	StatusUnknown Status = "unknown"
+	// StatusOK means the checked component is in its expected state.
+	StatusOK Status = "ok"
+	// StatusWarn means something is off but mail still flows.
+	StatusWarn Status = "warn"
+	// StatusError means mail delivery is (or soon will be) affected.
+	StatusError Status = "error"
+)
+
+// severity orders statuses so a group can report its worst member.
+func (s Status) severity() int {
+	switch s {
+	case StatusError:
+		return 3
+	case StatusWarn:
+		return 2
+	case StatusOK:
+		return 1
+	default:
+		return 0
+	}
+}
+
+// Worst returns the most severe of the given statuses, or StatusUnknown when
+// there are none. It is how the status page rolls a list of checks up into one
+// headline.
+func Worst(statuses ...Status) Status {
+	worst := StatusUnknown
+	for _, s := range statuses {
+		if s.severity() > worst.severity() {
+			worst = s
+		}
+	}
+	return worst
+}