Keep a facts snapshot for merge checks, and say when it goes stale (hq to-be 45 Phase 5, S14)

Every check the mesh had was right about the world it was given and none was given
the mesh's: a real machine's name made an identity too long (263), the node-engine
refused what the catalogue check passed (236). The controller now composes what a
check needs - every machine under a pseudonym of its name's length, its roles,
system, builds, capabilities, assignments, pins, settings and how its declaration
composes; every seat, module and source; the bus, store and node-engine versions it
runs - with no secret, no address and no name, and keeps it in the artifact store
as facts:latest when it moved, or daily. The replaced snapshot's manifest is let go
of, so the nightly collector takes it. S14 raises facts-stale past two days.

internal/inventory/reported.go

@@ -0,0 +1,42 @@
+package inventory
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"github.com/jackc/pgx/v5"
+)
+
+// Described is what a machine said about itself beyond its capabilities: the architecture and kernel
+// its node-engine runs on (novox/hq to-be 45 §9, the facts snapshot).
+type Described struct {
+	Architecture string `json:"architecture"`
+	Kernel       string `json:"kernel"`
+}
+
+// DescribedOf is the architecture and kernel a machine last reported; empty for one that never has.
+func (i *Inventory) DescribedOf(ctx context.Context, nodeName string) (Described, error) {
+	var raw []byte
+	err := i.store.Pool().QueryRow(ctx, `select profile from node where name = $1`, nodeName).Scan(&raw)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return Described{}, fmt.Errorf("%w: %s", ErrNoSuchNode, nodeName)
+	}
+	if err != nil || len(raw) == 0 {
+		return Described{}, err
+	}
+	var r Described
+	if err := json.Unmarshal(raw, &r); err != nil {
+		return Described{}, err
+	}
+	return r, nil
+}
+
+// ServerVersion is the store's own word for the release it runs — the version a test suite standing in
+// for it must run (novox/hq ADR 0227 rule 9).
+func (i *Inventory) ServerVersion(ctx context.Context) (string, error) {
+	var v string
+	err := i.store.Pool().QueryRow(ctx, `show server_version`).Scan(&v)
+	return v, err
+}