R-351: the restore compares where the backup says the data lived; second press cannot start a second run

Part 3 (not droppable) and the engine half of Part 2. No version bump yet - one bump and
one bake at the end of the session.

PART 3a - a second press really did start a second run. Established with a test BEFORE any
change: both offboxReconstituteHandler and offboxPlaceHandler answered "...elindult" and
overwrote the first restore's op/stack. Cause: every restore handler gated on
backupMgr.IsRunning() - the CONCURRENCY flag, which the restore goroutine acquires AFTER the
handler returns (offbox_reconstitute.go:180, offbox_restore.go:393). Seven sites. The wizard
had read the correct flag since v0.154.0 and said so in a comment; the handlers never moved.
New Server.restoreOpBlocked() reads BOTH flags - the display flag covers the whole off-box
restore, the concurrency flag is the only one the nightly backup holds - and the refusal now
names the running app and a route.

PART 3b - the page DOES refresh; the defect was the RESULT. backups_shared.html gated the
terminal result on a page-local sawRunning flag, so a restore that finished before the page
was opened, or inside one 3s poll, was shown to nobody. The 2026-08-21 OpenGist restore took
8.666s and no screen ever said it completed - the answer existed only in docker logs.
RestoreOpStatus.LastRecent now carries the server's verdict. The 10-minute window moved to
internal/backup as RestoreResultWindow and internal/web's constant is an alias: one
expression, two surfaces. Also removed the wizard's self-contradiction, which said the state
refreshes automatically AND that you must refresh the page.

PART 2 (engine) - every recovery unit manifest has carried drive and namespace_root since
schema 1, and NO non-test code read either back. The reconstitution opened the manifest and
took only the coherence stamp, then resolved its destination from the live app. A restore
into a different destination succeeded silently under a green message. New
backup/offbox_placement.go: CheckPlacement (pure, total), PlacementMismatchMessage,
recordedPlacementFromScratch. Compared before the safety dump and before the first byte.
A mismatch is NAMED and refused; ackPlacementChange lets the customer proceed deliberately -
a separate field from confirm=1, because one click must not carry two decisions. An UNKNOWN
recording is never a mismatch: refusing on an absence would strand every pre-field unit.
The not-installed refusal (R-253) now names the drive the backup recorded.

RED-PROOFS, each mutation asserted applied and reverted to 0:
  B  both guards removed (count asserted 2) -> the restore WAS seen starting with no drive
     attached: no error, full 3.00s run, wrote into /tmp/mutant-destination
  C  Mismatch forced false -> the silent divergent restore returned
  E  Known() forced true  -> the fabricated empty prefill appeared
  D  Mismatch forced true -> 8 ordinary reconstitute tests broke, proving reachability both ways
Note on D: the existing fixtures write a schema-1 manifest with NO drive, so they are
scenario-E shaped. The matching case is covered in the scenario table, not by them.

Gates 11/11 OK. Suite 28 packages ok. Hungarian verified as hex, no BOM, no mojibake sentinels.

NOT in this commit, still open: Part 2's scenario-A prefill UI, Part 1's deploy-page
visibility line, Part 1's specification document, Part 4's measurement.

controller/internal/backup/offbox_reconstitute_test.go

@@ -174,7 +174,7 @@ func reconFixture(t *testing.T, runID, dumpsAt string, dumpBody string) (*Manage
 func TestReconstituteReplaysDBAndOrdersOperations(t *testing.T) {
 	m, prov, imported := reconFixture(t, "20260719T060000Z", "2026-07-19T06:00:00Z", pgDump(1))
 
-	res, err := m.ReconstituteFromOffsite(context.Background(), "immich")
+	res, err := m.ReconstituteFromOffsite(context.Background(), "immich", false)
 	if err != nil {
 		t.Fatalf("reconstitute: %v", err)
 	}
@@ -220,7 +220,7 @@ func TestReconstituteRefusesWhenSafetyDumpFails(t *testing.T) {
 	var copied bool
 	m.SetOffboxFullPlaceCopier(func(_, _ string) (int, error) { copied = true; return 1, nil })
 
-	_, err := m.ReconstituteFromOffsite(context.Background(), "immich")
+	_, err := m.ReconstituteFromOffsite(context.Background(), "immich", false)
 	if err == nil {
 		t.Fatal("expected a refusal when the safety dump cannot be taken")
 	}
@@ -246,7 +246,7 @@ func TestReconstituteNoDBAppMakesNoDumpOrImportCalls(t *testing.T) {
 		return DumpResult{DB: d}
 	})
 
-	res, err := m.ReconstituteFromOffsite(context.Background(), "immich")
+	res, err := m.ReconstituteFromOffsite(context.Background(), "immich", false)
 	if err != nil {
 		t.Fatalf("reconstitute: %v", err)
 	}
@@ -267,7 +267,7 @@ func TestReconstituteNoDBAppMakesNoDumpOrImportCalls(t *testing.T) {
 func TestReconstituteSurfacesLegacySkewedPair(t *testing.T) {
 	m, _, imported := reconFixture(t, "", "", pgDump(1))
 
-	res, err := m.ReconstituteFromOffsite(context.Background(), "immich")
+	res, err := m.ReconstituteFromOffsite(context.Background(), "immich", false)
 	if err != nil {
 		t.Fatalf("a legacy pair must still be restorable, got refusal: %v", err)
 	}
@@ -286,7 +286,7 @@ func TestReconstituteFlagsCustomerEmptyDump(t *testing.T) {
 	// A valid postgres dump whose accounts table has NO rows — the 2026-07-19 shape exactly.
 	m, _, _ := reconFixture(t, "run1", "2026-07-19T06:00:00Z", pgDump(0))
 
-	res, err := m.ReconstituteFromOffsite(context.Background(), "immich")
+	res, err := m.ReconstituteFromOffsite(context.Background(), "immich", false)
 	if err != nil {
 		t.Fatalf("the sniff must never block a restore: %v", err)
 	}