v0.318.0: the internal data place, partitions, an honest whole-box backup offer (R-1084), sys_drive never offered (R-1082)

felhom.eu architecture/16 §4-§6 (build B). MinAgent 0.157.0 — the internal place and the partitions appear only when
agent >= 0.158.0 reports them. Tests red-proved; four parity fixtures refreshed (only the new lines).

Claude-Session: https://claude.ai/code/session_012qRErfCoiTkvDK9N5XHbzb

controller/internal/stacks/d4_needs_drive_test.go

@@ -2,8 +2,13 @@ package stacks
 
 import (
 	"errors"
+	"io"
+	"log"
+	"path/filepath"
 	"strings"
 	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-controller/internal/settings"
 )
 
 // D4 (felhom.eu architecture/16-storage-physical-identity.md §5, R-1068): a data-folder or media app on a
@@ -45,3 +50,33 @@ func TestD4_FilledPathKeepsItsOwnRefusal(t *testing.T) {
 		t.Fatalf("want ErrPathMissing for a filled, missing path, got %v", err)
 	}
 }
+
+// `16` §5 (v0.318.0): on a one-disk box with the internal place registered, a media app installs with NO extra step
+// and NO sentence — its HDD_PATH lands on the internal place. Companion of TestD4_NoDriveRefusalSpeaksInWords (the
+// same app, no drive → the refusal).
+func TestD4_InternalPlaceIsTheMediaAppsDrive(t *testing.T) {
+	m := r553Manager(t, "display_name: Jellyfin\nmedia_library:\n  folder: films\ndeploy_fields:\n  - env_var: HDD_PATH\n    label: Médiatár útvonal\n    type: path\n    required: true\n")
+	sett, err := settings.Load(filepath.Join(t.TempDir(), "settings.json"), log.New(io.Discard, "", 0))
+	if err != nil {
+		t.Fatal(err)
+	}
+	belso := filepath.Join(t.TempDir(), "belso")
+	if err := sett.AddStoragePath(settings.StoragePath{Path: belso, IsDefault: true, Schedulable: true, Kind: settings.StorageKindInternal}); err != nil {
+		t.Fatal(err)
+	}
+	m.settings = sett
+	m.isMountPoint = func(p string) bool { return filepath.Clean(p) == belso }
+	if got := m.defaultMediaDrive(); got != belso {
+		t.Fatalf("the default media drive: want the internal place %q, got %q", belso, got)
+	}
+	// The folder is deliberately NOT created: the deploy then stops at its path check, so no real `docker compose`
+	// can ever start on the machine running this test (tests that reach real docker act on DooPlex, R-650). The
+	// refusal naming the internal place proves HDD_PATH was filled with it — the step the household no longer does.
+	_, err = m.DeployStack(DeployRequest{StackName: "r553app", Values: map[string]string{}})
+	if errors.Is(err, ErrNeedsDrive) {
+		t.Fatalf("a box with the internal place must not be told it needs a drive: %v", err)
+	}
+	if !errors.Is(err, ErrPathMissing) || !strings.Contains(err.Error(), belso) {
+		t.Fatalf("want the media app's HDD_PATH filled with the internal place %q, got %v", belso, err)
+	}
+}