diff --git a/tools/tht/internal/authprojection/projection_linux.go b/tools/tht/internal/authprojection/projection_linux.go
index 246549a6..ceb6996e 100644
--- a/tools/tht/internal/authprojection/projection_linux.go
+++ b/tools/tht/internal/authprojection/projection_linux.go
@@ -16,6 +16,9 @@ import (
 const maximumDirectoryEntries = 16
 
 type testHooks struct {
+	beforeFlock         func(int)
+	beforeStageWrite    func() error
+	beforeStageFsync    func() error
 	beforeStageRename   func() error
 	beforeCurrentRename func() error
 	beforeFinalVerify   func() error
@@ -49,6 +52,15 @@ func hook(selectHook func(testHooks) func() error) error {
 	return nil
 }
 
+func rendezvousBeforeFlock(root int) {
+	hookState.Lock()
+	callback := hookState.hooks.beforeFlock
+	hookState.Unlock()
+	if callback != nil {
+		callback(root)
+	}
+}
+
 func Inspect(spec Spec) (Status, error) {
 	root, err := openRoot(spec)
 	if err != nil {
@@ -63,16 +75,12 @@ func Begin(spec Spec, before *Snapshot, requireReadyMatch bool) (*Transaction, e
 	if err != nil {
 		return nil, err
 	}
+	rendezvousBeforeFlock(root)
 	if unix.Flock(root, unix.LOCK_EX) != nil {
 		unix.Close(root)
 		return nil, ErrIntegrity
 	}
 	transaction := &Transaction{spec: spec, before: before, rootFD: root, lockFD: root}
-	if ensureGenerations(root, spec) != nil {
-		_ = transaction.Close()
-		return nil, ErrIntegrity
-	}
-
 	selector, selectorErr := readSelector(root, spec)
 	switch {
 	case selectorErr == nil && selector.State == "blocked":
@@ -81,7 +89,7 @@ func Begin(spec Spec, before *Snapshot, requireReadyMatch bool) (*Transaction, e
 			return nil, ErrIntegrity
 		}
 	case selectorErr == nil:
-		if validateRootEntries(root, spec) != nil {
+		if recoverCurrentTemporaries(root, spec) != nil || validateRootEntries(root, spec) != nil {
 			_ = transaction.Close()
 			return nil, ErrIntegrity
 		}
@@ -98,7 +106,10 @@ func Begin(spec Spec, before *Snapshot, requireReadyMatch bool) (*Transaction, e
 	case currentExists(root):
 		_ = transaction.Close()
 		return nil, ErrIntegrity
-	case requireReadyMatch || validateInitialRootEntries(root, spec) != nil:
+	case requireReadyMatch || validateEmptyRootEntries(root, spec) != nil:
+		_ = transaction.Close()
+		return nil, ErrIntegrity
+	case ensureGenerations(root, spec) != nil:
 		_ = transaction.Close()
 		return nil, ErrIntegrity
 	}
@@ -135,7 +146,7 @@ func (transaction *Transaction) Commit(after Snapshot) (Status, error) {
 	if writeSelector(transaction.rootFD, transaction.spec, selector) != nil {
 		return Status{}, ErrIntegrity
 	}
-	status, err := inspectFD(transaction.rootFD, transaction.spec)
+	status, err := inspectSelectedGeneration(transaction.rootFD, transaction.spec, selector)
 	if err != nil || status.Snapshot.Generation != after.Generation {
 		return Status{}, ErrIntegrity
 	}
@@ -146,6 +157,10 @@ func (transaction *Transaction) Commit(after Snapshot) (Status, error) {
 	if retain(transaction.rootFD, transaction.spec, selector) != nil {
 		return Status{}, ErrIntegrity
 	}
+	status, err = inspectFD(transaction.rootFD, transaction.spec)
+	if err != nil || status.Snapshot.Generation != after.Generation {
+		return Status{}, ErrIntegrity
+	}
 	return status, nil
 }
 
@@ -313,9 +328,9 @@ func validateRootEntries(root int, spec Spec) error {
 	}
 	return nil
 }
-func validateInitialRootEntries(root int, spec Spec) error {
+func validateEmptyRootEntries(root int, spec Spec) error {
 	names, err := scanDirectoryNames(root, spec)
-	if err != nil || len(names) != 1 || !names["generations"] {
+	if err != nil || len(names) != 0 {
 		return ErrIntegrity
 	}
 	return nil
@@ -332,6 +347,20 @@ func inspectFD(root int, spec Spec) (Status, error) {
 	return inspectCapturedSelector(root, spec, selector)
 }
 func inspectCapturedSelector(root int, spec Spec, selector Selector) (Status, error) {
+	if selector.State == "blocked" {
+		return Status{Selector: selector}, ErrBlocked
+	}
+	status, err := inspectSelectedGeneration(root, spec, selector)
+	if err != nil {
+		return Status{}, err
+	}
+	if validateReadyGenerationNamespace(root, spec, selector) != nil {
+		return Status{}, ErrIntegrity
+	}
+	return status, nil
+}
+
+func inspectSelectedGeneration(root int, spec Spec, selector Selector) (Status, error) {
 	if selector.State == "blocked" {
 		return Status{Selector: selector}, ErrBlocked
 	}
@@ -342,6 +371,34 @@ func inspectCapturedSelector(root int, spec Spec, selector Selector) (Status, er
 	return Status{Selector: selector, Snapshot: snapshot}, nil
 }
 
+func validateReadyGenerationNamespace(root int, spec Spec, selector Selector) error {
+	generations, err := openDirectoryAt(root, "generations", spec)
+	if err != nil {
+		return ErrIntegrity
+	}
+	defer unix.Close(generations)
+	names, err := scanDirectoryNames(generations, spec)
+	if err != nil {
+		return ErrIntegrity
+	}
+	keep := map[string]bool{selector.Generation: true}
+	for _, generation := range selector.PreviousGenerations {
+		keep[generation] = true
+	}
+	if len(names) != len(keep) {
+		return ErrIntegrity
+	}
+	for name := range names {
+		if !validHex(name, 64) || !keep[name] {
+			return ErrIntegrity
+		}
+		if _, err := readGeneration(root, spec, name); err != nil {
+			return ErrIntegrity
+		}
+	}
+	return nil
+}
+
 func readSelector(root int, spec Spec) (Selector, error) {
 	data, err := readRegularAt(root, "CURRENT", spec, maximumSelectorBytes)
 	if err != nil {
@@ -516,7 +573,7 @@ func stageGeneration(root int, spec Spec, transactionID string, snapshot Snapsho
 		if found, readErr := readGeneration(root, spec, snapshot.Generation); readErr == nil && found.Generation == snapshot.Generation {
 			return nil
 		}
-		if removeConfinedDirectory(generations, snapshot.Generation, spec, false) != nil {
+		if !currentMatchesBlockedTransaction(root, spec, transactionID) || removeConfinedDirectory(generations, snapshot.Generation, spec, false) != nil {
 			return ErrIntegrity
 		}
 	} else if !errors.Is(err, unix.ENOENT) {
@@ -546,7 +603,16 @@ func stageGeneration(root int, spec Spec, transactionID string, snapshot Snapsho
 	if err != nil {
 		return ErrIntegrity
 	}
-	if writeRegularAt(stage, "auth.yaml", spec, snapshot.Auth) != nil || (snapshot.Mode == "local" && writeRegularAt(stage, "users.yaml", spec, snapshot.Users) != nil) || writeRegularAt(stage, "manifest.json", spec, manifestData) != nil || unix.Fsync(stage) != nil {
+	if err := hook(func(h testHooks) func() error { return h.beforeStageWrite }); err != nil {
+		return err
+	}
+	if writeRegularAt(stage, "auth.yaml", spec, snapshot.Auth) != nil || (snapshot.Mode == "local" && writeRegularAt(stage, "users.yaml", spec, snapshot.Users) != nil) || writeRegularAt(stage, "manifest.json", spec, manifestData) != nil {
+		return ErrIntegrity
+	}
+	if err := hook(func(h testHooks) func() error { return h.beforeStageFsync }); err != nil {
+		return err
+	}
+	if unix.Fsync(stage) != nil {
 		return ErrIntegrity
 	}
 	if err := hook(func(h testHooks) func() error { return h.beforeStageRename }); err != nil {
@@ -622,6 +688,13 @@ func recoverTemporary(root int, spec Spec, blocked Selector) error {
 			return ErrIntegrity
 		}
 	}
+	if unix.Fsync(generations) != nil {
+		return ErrIntegrity
+	}
+	return recoverCurrentTemporaries(root, spec)
+}
+
+func recoverCurrentTemporaries(root int, spec Spec) error {
 	rootNames, err := scanDirectoryNames(root, spec)
 	if err != nil || !rootNames["CURRENT"] || !rootNames["generations"] {
 		return ErrIntegrity
@@ -643,11 +716,16 @@ func recoverTemporary(root int, spec Spec, blocked Selector) error {
 			return ErrIntegrity
 		}
 	}
-	if unix.Fsync(generations) != nil || unix.Fsync(root) != nil {
+	if unix.Fsync(root) != nil {
 		return ErrIntegrity
 	}
 	return nil
 }
+
+func currentMatchesBlockedTransaction(root int, spec Spec, transactionID string) bool {
+	selector, err := readSelector(root, spec)
+	return err == nil && selector.State == "blocked" && selector.Transaction == transactionID
+}
 func stageGenerationName(name, transactionID string) (string, bool) {
 	prefix := ".stage-" + transactionID + "-"
 	if len(name) != len(prefix)+64 || name[:len(prefix)] != prefix {
diff --git a/tools/tht/internal/authprojection/projection_linux_test.go b/tools/tht/internal/authprojection/projection_linux_test.go
index 18835066..2613ebc5 100644
--- a/tools/tht/internal/authprojection/projection_linux_test.go
+++ b/tools/tht/internal/authprojection/projection_linux_test.go
@@ -11,7 +11,6 @@ import (
 	"sync"
 	"syscall"
 	"testing"
-	"time"
 
 	"golang.org/x/sys/unix"
 )
@@ -85,9 +84,7 @@ func TestInspectRejectsMissingBlockedMalformedAndTamperedCurrent(t *testing.T) {
 	if _, err := Inspect(spec); !errors.Is(err, ErrIntegrity) {
 		t.Fatalf("malformed error = %v", err)
 	}
-	if err := os.Remove(filepath.Join(spec.RuntimeRoot, "CURRENT")); err != nil {
-		t.Fatal(err)
-	}
+	spec = testSpec(t)
 	commitSnapshot(t, spec, testSnapshot(t, "tampered"))
 	if err := os.WriteFile(filepath.Join(spec.RuntimeRoot, "CURRENT"), []byte(`{"version":1,"state":"ready"}`), runtimeFileMode); err != nil {
 		t.Fatal(err)
@@ -220,12 +217,161 @@ func TestInspectRejectsUnexpectedGenerationEntry(t *testing.T) {
 	}
 }
 
+func TestInspectRejectsReadyNamespaceOutsideCurrentHistory(t *testing.T) {
+	for _, tc := range []struct {
+		name   string
+		mutate func(t *testing.T, spec Spec, status Status)
+	}{
+		{"extra generation", func(t *testing.T, spec Spec, _ Status) {
+			name := strings.Repeat("e", 64)
+			if err := os.Mkdir(filepath.Join(spec.RuntimeRoot, "generations", name), runtimeDirectoryMode); err != nil {
+				t.Fatal(err)
+			}
+		}},
+		{"stage", func(t *testing.T, spec Spec, _ Status) {
+			name := ".stage-" + strings.Repeat("a", 32) + "-" + strings.Repeat("e", 64)
+			if err := os.Mkdir(filepath.Join(spec.RuntimeRoot, "generations", name), runtimeDirectoryMode); err != nil {
+				t.Fatal(err)
+			}
+		}},
+		{"corrupt predecessor", func(t *testing.T, spec Spec, status Status) {
+			if len(status.Selector.PreviousGenerations) != 1 {
+				t.Fatalf("history = %#v", status.Selector.PreviousGenerations)
+			}
+			path := filepath.Join(spec.RuntimeRoot, "generations", status.Selector.PreviousGenerations[0], "auth.yaml")
+			if err := os.WriteFile(path, []byte("tampered"), runtimeFileMode); err != nil {
+				t.Fatal(err)
+			}
+		}},
+		{"missing predecessor", func(t *testing.T, spec Spec, status Status) {
+			if len(status.Selector.PreviousGenerations) != 1 {
+				t.Fatalf("history = %#v", status.Selector.PreviousGenerations)
+			}
+			if err := os.RemoveAll(filepath.Join(spec.RuntimeRoot, "generations", status.Selector.PreviousGenerations[0])); err != nil {
+				t.Fatal(err)
+			}
+		}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			spec := testSpec(t)
+			commitSnapshot(t, spec, testSnapshot(t, "prior-"+tc.name))
+			status := commitSnapshot(t, spec, testSnapshot(t, "current-"+tc.name))
+			tc.mutate(t, spec, status)
+			if _, err := Inspect(spec); !errors.Is(err, ErrIntegrity) {
+				t.Fatalf("Inspect error = %v", err)
+			}
+		})
+	}
+}
+
+func TestBeginRecoversStrictCurrentTemporaryBesideReadySelector(t *testing.T) {
+	spec := testSpec(t)
+	prior := testSnapshot(t, "ready-temporary")
+	commitSnapshot(t, spec, prior)
+	temporaryID := strings.Repeat("a", 32)
+	temporary, err := encodeSelector(Selector{Version: SchemaVersion, State: "blocked", Transaction: temporaryID})
+	if err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(spec.RuntimeRoot, ".current-"+temporaryID+".tmp")
+	if err := os.WriteFile(path, temporary, runtimeFileMode); err != nil {
+		t.Fatal(err)
+	}
+	transaction, err := Begin(spec, &prior, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer transaction.Close()
+	if transaction.prior == nil || transaction.prior.Snapshot.Generation != prior.Generation {
+		t.Fatalf("prior = %#v", transaction.prior)
+	}
+	if _, err := os.Lstat(path); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("ready temporary remains: %v", err)
+	}
+}
+
+func TestBeginRejectsMalformedCurrentWithoutCreatingGenerations(t *testing.T) {
+	spec := testSpec(t)
+	if err := os.WriteFile(filepath.Join(spec.RuntimeRoot, "CURRENT"), []byte("malformed"), runtimeFileMode); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := Begin(spec, nil, false); !errors.Is(err, ErrIntegrity) {
+		t.Fatalf("Begin error = %v", err)
+	}
+	if _, err := os.Lstat(filepath.Join(spec.RuntimeRoot, "generations")); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("Begin mutated malformed root: %v", err)
+	}
+}
+
+func TestCommitRefusesCorruptTargetUnlessCurrentIsMatchingBlockedTransaction(t *testing.T) {
+	for _, tc := range []struct {
+		name    string
+		current func(t *testing.T, root string, transaction string, snapshot Snapshot)
+	}{
+		{"ready", func(t *testing.T, root, _ string, snapshot Snapshot) {
+			data, err := encodeSelector(Selector{Version: SchemaVersion, State: "ready", Transaction: strings.Repeat("b", 32), Generation: snapshot.Generation})
+			if err != nil {
+				t.Fatal(err)
+			}
+			if err := os.WriteFile(filepath.Join(root, "CURRENT"), data, runtimeFileMode); err != nil {
+				t.Fatal(err)
+			}
+		}},
+		{"malformed", func(t *testing.T, root, _ string, _ Snapshot) {
+			if err := os.WriteFile(filepath.Join(root, "CURRENT"), []byte("malformed"), runtimeFileMode); err != nil {
+				t.Fatal(err)
+			}
+		}},
+		{"other blocked transaction", func(t *testing.T, root, transaction string, _ Snapshot) {
+			other := strings.Repeat("b", 32)
+			if other == transaction {
+				other = strings.Repeat("c", 32)
+			}
+			data, err := encodeSelector(Selector{Version: SchemaVersion, State: "blocked", Transaction: other})
+			if err != nil {
+				t.Fatal(err)
+			}
+			if err := os.WriteFile(filepath.Join(root, "CURRENT"), data, runtimeFileMode); err != nil {
+				t.Fatal(err)
+			}
+		}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			spec := testSpec(t)
+			snapshot := testSnapshot(t, "corrupt-"+tc.name)
+			transaction, err := Begin(spec, nil, false)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer transaction.Close()
+			target := filepath.Join(spec.RuntimeRoot, "generations", snapshot.Generation)
+			if err := os.Mkdir(target, runtimeDirectoryMode); err != nil {
+				t.Fatal(err)
+			}
+			for _, name := range []string{"auth.yaml", "users.yaml", "manifest.json"} {
+				if err := os.WriteFile(filepath.Join(target, name), []byte("corrupt"), runtimeFileMode); err != nil {
+					t.Fatal(err)
+				}
+			}
+			tc.current(t, spec.RuntimeRoot, transaction.transactionID, snapshot)
+			if _, err := transaction.Commit(snapshot); !errors.Is(err, ErrIntegrity) {
+				t.Fatalf("Commit error = %v", err)
+			}
+			if _, err := os.Lstat(target); err != nil {
+				t.Fatalf("corrupt target was removed: %v", err)
+			}
+		})
+	}
+}
+
 func TestCommitLeavesBlockedAfterInjectedStageWriteFsyncRenameAndVerifyFailure(t *testing.T) {
 	for _, tc := range []struct {
 		name  string
 		hooks testHooks
 	}{
-		{"stage", testHooks{beforeStageRename: func() error { return errors.New("sentinel") }}},
+		{"stage write", testHooks{beforeStageWrite: func() error { return errors.New("sentinel") }}},
+		{"stage fsync", testHooks{beforeStageFsync: func() error { return errors.New("sentinel") }}},
+		{"stage rename", testHooks{beforeStageRename: func() error { return errors.New("sentinel") }}},
 		{"current", testHooks{beforeCurrentRename: func() error { return errors.New("sentinel") }}},
 		{"verify", testHooks{beforeFinalVerify: func() error { return errors.New("sentinel") }}},
 	} {
@@ -474,21 +620,30 @@ func TestConcurrentBeginSerializesAcrossCurrentRenameWithoutCreatingLockEntry(t
 	if err != nil {
 		t.Fatal(err)
 	}
-	started := make(chan struct{})
+	checked := make(chan error, 1)
+	restore := setTestHooksForTest(testHooks{beforeFlock: func(fd int) {
+		if err := unix.Flock(fd, unix.LOCK_EX|unix.LOCK_NB); !errors.Is(err, unix.EWOULDBLOCK) {
+			checked <- fmt.Errorf("nonblocking flock error = %v", err)
+			return
+		}
+		checked <- nil
+	}})
+	defer restore()
 	finished := make(chan error, 1)
 	go func() {
-		close(started)
 		second, err := Begin(spec, nil, false)
 		if err == nil {
 			err = second.Close()
 		}
 		finished <- err
 	}()
-	<-started
+	if err := <-checked; err != nil {
+		t.Fatal(err)
+	}
 	select {
 	case err := <-finished:
 		t.Fatalf("second Begin did not block: %v", err)
-	case <-time.After(50 * time.Millisecond):
+	default:
 	}
 	if err := first.Close(); err != nil {
 		t.Fatal(err)