feat(dict): make the build's dictionary version deploy-authoritative

The dictionary lives on a persistent volume seeded from the image once and never
re-seeded, so a redeploy that bumped BACKEND_DICT_VERSION left the new DAWGs
unreachable (the volume mount shadows the image copy) and the active version stuck
at whatever the admin console last installed — a native offline-first client then
fetched the server's older pinned version over the network instead of using its
bundled dict.

On boot the backend now DELIVERS the build version onto the volume add-only, from a
second unshadowed image copy at BACKEND_DICT_SEED_DIR, into DICT_DIR/<version>/ when
absent (the flat seed and prior uploads untouched, so in-flight games keep theirs),
and InitActiveVersion makes the build version active — except a console-installed
version NEWER than the build (compared numerically) is not downgraded by a restart.
The .seed_version guard still protects the flat seed's label (a bump is a new
subdirectory, never a relabel). The console stays for out-of-band updates.

Docs: ARCHITECTURE.md §5, deploy/README.md, seedmarker.go. Tests: engine.DeliverVersion
(add-only, idempotent, flat-seed skip), compareDictVersions, and the dictionary-update
integration test's deploy-delivers path.

backend/internal/game/config.go

@@ -18,6 +18,13 @@ type Config struct {
 	// DictVersion labels the dictionary version new games pin. Sourced from
 	// BACKEND_DICT_VERSION.
 	DictVersion string
+	// DictSeedDir holds the image's read-only copy of the build's DictVersion DAWGs,
+	// on a path the persistent DictDir volume does NOT shadow. On boot the backend
+	// delivers this version into DictDir/<DictVersion>/ if absent (add-only), so a
+	// redeploy that bumped DICT_VERSION makes the new dictionary resident and activatable
+	// without disturbing the versions in-flight games already pin. Sourced from
+	// BACKEND_DICT_SEED_DIR; empty disables delivery (the pre-existing seed-only behaviour).
+	DictSeedDir string
 	// TimeoutSweepInterval is how often the sweeper scans for overdue turns.
 	// Sourced from BACKEND_GAME_TIMEOUT_SWEEP_INTERVAL.
 	TimeoutSweepInterval time.Duration

backend/internal/game/service.go

@@ -232,21 +232,31 @@ func (svc *Service) ActiveVersion() string {
 }
 
 // InitActiveVersion reconciles the persisted active dictionary version with the
-// registry at startup. If a version was persisted and is resident, it becomes the
-// active version; otherwise the configured seed version is kept and persisted as
-// the initial active version. Call once during wiring, before serving traffic.
+// registry at startup and makes the build's version (BACKEND_DICT_VERSION, delivered
+// resident by engine.DeliverVersion) authoritative: a redeploy that bumped the build
+// version thus activates it for new games without any admin step, while old games keep
+// the version they pin. The one exception is a version installed out-of-band through
+// the admin console that is NEWER than the build version and still resident — it is
+// kept, so a restart on an older image never downgrades a hotfix. A build version that
+// is not resident (delivery disabled or a partial state) falls back to a resident
+// persisted version. The chosen version is persisted so the admin console reflects it.
+// Call once during wiring, before serving traffic.
 func (svc *Service) InitActiveVersion(ctx context.Context) error {
 	persisted, ok, err := svc.store.GetActiveDictVersion(ctx)
 	if err != nil {
 		return err
 	}
-	if ok && svc.versionResident(persisted) {
-		svc.verMu.Lock()
-		svc.version = persisted
-		svc.verMu.Unlock()
-		return nil
+	target := svc.activeVersion() // the build seed version (config.DictVersion)
+	if ok && svc.versionResident(persisted) && compareDictVersions(persisted, target) > 0 {
+		target = persisted // a newer out-of-band install wins over the build version
 	}
-	return svc.store.SetActiveDictVersion(ctx, svc.activeVersion())
+	if !svc.versionResident(target) && ok && svc.versionResident(persisted) {
+		target = persisted // the build version is unloadable — keep a resident one
+	}
+	svc.verMu.Lock()
+	svc.version = target
+	svc.verMu.Unlock()
+	return svc.store.SetActiveDictVersion(ctx, target)
 }
 
 // SetActiveVersion records version as the active dictionary version, persisting it

backend/internal/game/version.go

@@ -0,0 +1,45 @@
+package game
+
+import (
+	"strconv"
+	"strings"
+)
+
+// compareDictVersions orders two dictionary version labels of the shape "vMAJOR.MINOR.PATCH"
+// numerically, returning -1, 0 or +1 as a is less than, equal to or greater than b. Labels
+// that do not parse fall back to a byte comparison, so the ordering is always total (a mixed
+// or malformed pair never crashes the boot-time active-version reconcile).
+func compareDictVersions(a, b string) int {
+	pa, oka := parseDictVersion(a)
+	pb, okb := parseDictVersion(b)
+	if !oka || !okb {
+		return strings.Compare(a, b)
+	}
+	for i := range pa {
+		if pa[i] != pb[i] {
+			if pa[i] < pb[i] {
+				return -1
+			}
+			return 1
+		}
+	}
+	return 0
+}
+
+// parseDictVersion parses a "vMAJOR.MINOR.PATCH" label into its three numeric parts, reporting
+// whether it matched that shape.
+func parseDictVersion(v string) ([3]int, bool) {
+	parts := strings.Split(strings.TrimPrefix(v, "v"), ".")
+	if len(parts) != 3 {
+		return [3]int{}, false
+	}
+	var out [3]int
+	for i, p := range parts {
+		n, err := strconv.Atoi(p)
+		if err != nil {
+			return [3]int{}, false
+		}
+		out[i] = n
+	}
+	return out, true
+}

backend/internal/game/version_test.go

@@ -0,0 +1,37 @@
+package game
+
+import "testing"
+
+func TestCompareDictVersions(t *testing.T) {
+	cases := []struct {
+		a, b string
+		want int
+	}{
+		{"v1.3.0", "v1.3.1", -1},
+		{"v1.3.1", "v1.3.0", 1},
+		{"v1.3.1", "v1.3.1", 0},
+		{"v1.3.9", "v1.3.10", -1}, // numeric, not lexical
+		{"v1.10.0", "v1.9.0", 1},
+		{"v2.0.0", "v1.9.9", 1},
+		{"1.3.1", "v1.3.1", 0}, // the leading v is optional
+		// Non-semver falls back to a byte comparison, keeping the ordering total.
+		{"weird", "weird", 0},
+		{"a", "b", -1},
+	}
+	for _, c := range cases {
+		if got := compareDictVersions(c.a, c.b); sign(got) != c.want {
+			t.Errorf("compareDictVersions(%q, %q) = %d, want sign %d", c.a, c.b, got, c.want)
+		}
+	}
+}
+
+func sign(n int) int {
+	switch {
+	case n < 0:
+		return -1
+	case n > 0:
+		return 1
+	default:
+		return 0
+	}
+}