refactor(cordn): move the file stores and EncryptedAppendLog to commonMain on okio

FileCordnStores (CordnStorageLayout and the group, key-package,
coordinator and handoff stores), FileBackedCordnScopeFactory,
CordnMigrationStores and EncryptedAppendLog move from jvmAndroid to
commonMain. They now take an okio Path, plus a FileSystem that defaults
to platformFileSystem, where they used to take a java.io.File.

The on-disk format does not change. These files hold encrypted MLS group
state that cannot be re-derived, so CordnStorageFormatGoldenTest pinned
the exact tree of paths and the bytes of every file against the java.io
implementation first. It passes against this one with its constants
untouched; only its construction glue moved from File to Path.

- Cursor framing: ByteBuffer's default big-endian putLong/getLong is now
  okio Buffer.writeLong/readLong, which is also big-endian.
- Migration base64: java.util.Base64 is now
  kotlin.io.encoding.Base64.Default with PRESENT_OPTIONAL padding, the
  same alphabet and output. A new test checks it against java.util.Base64
  in both directions, padded and unpadded.
- Failure handling: File.delete(), deleteRecursively() and
  renameTo-else-copy returned false where okio throws, so the File
  behaviour is kept by deleteQuietly, deleteRecursivelyQuietly and
  moveOrCopy in commons/util/FileSystemExt.kt.
- Durability: the log's fsyncs are FileHandle.flush(), which is
  FileDescriptor.sync() on the JVM and Android.

Callers updated: the CLI's CordnContext, CordnRuntime,
Account.cordnFilesDir (now Path?), AccountCacheState, and
EncryptedMarmotMessageStore, which stays in jvmAndroid and passes
toOkioPath() to the log.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S7FuNBSKiyVecARSoE4B9P

amethyst/src/main/java/com/vitorpamplona/amethyst/model/Account.kt

@@ -364,6 +364,7 @@ import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
+import okio.Path
 import kotlin.coroutines.cancellation.CancellationException
 import com.vitorpamplona.quartz.experimental.nip95.header.thumbhash as nip95thumbhash
 import com.vitorpamplona.quartz.experimental.profileGallery.thumbhash as galleryThumbhash
@@ -412,7 +413,7 @@ class Account(
      * Nothing about it is shared with Marmot's stores above — cordn has its
      * own, by the §3.1 rule in `amethyst/plans/2026-09-19-cordn-ui.md`.
      */
-    val cordnFilesDir: java.io.File? = null,
+    val cordnFilesDir: Path? = null,
     val mlsGroupStateStore: MlsGroupStateStore? = null,
     val marmotMessageStore: com.vitorpamplona.quartz.marmot.groups.MarmotMessageStore? = null,
     val marmotKeyPackageStore: com.vitorpamplona.quartz.marmot.mip00KeyPackages.KeyPackageBundleStore? = null,

amethyst/src/main/java/com/vitorpamplona/amethyst/model/accountsCache/AccountCacheState.kt

@@ -380,7 +380,7 @@ class AccountCacheState(
             // The same per-account directory the Marmot stores use. cordn
             // scopes itself further by coordinator underneath it, because a
             // gid is unique only within one (spec/00.md §4).
-            cordnFilesDir = accountDir,
+            cordnFilesDir = accountDir.toOkioPath(),
             mlsGroupStateStore = mlsStore,
             marmotMessageStore = marmotMessageStore,
             marmotKeyPackageStore = marmotKeyPackageStore,

amethyst/src/main/java/com/vitorpamplona/amethyst/model/cordn/CordnRuntime.kt

@@ -46,6 +46,8 @@ import com.vitorpamplona.amethyst.commons.cordn.FileCordnKeyPackageStore
 import com.vitorpamplona.amethyst.commons.cordn.KeyStoreCordnBlobCipher
 import com.vitorpamplona.amethyst.commons.cordn.OpenedWelcome
 import com.vitorpamplona.amethyst.commons.model.cordnGroups.CordnGroupList
+import com.vitorpamplona.amethyst.commons.util.deleteRecursivelyQuietly
+import com.vitorpamplona.amethyst.commons.util.platformFileSystem
 import com.vitorpamplona.quartz.contextvm.core.CvmKinds
 import com.vitorpamplona.quartz.cordn.appMultiDevice.CordnHandoffCode
 import com.vitorpamplona.quartz.cordn.spec00Coordinator.CoordinatorServerInfo
@@ -71,7 +73,7 @@ import kotlinx.coroutines.launch
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
-import java.io.File
+import okio.Path
 import kotlin.coroutines.cancellation.CancellationException
 import kotlin.uuid.ExperimentalUuidApi
 import kotlin.uuid.Uuid
@@ -98,7 +100,7 @@ import kotlin.uuid.Uuid
 class CordnRuntime(
     private val accountSigner: NostrSigner,
     private val client: INostrClient,
-    private val filesDir: File,
+    private val filesDir: Path,
     private val scope: CoroutineScope,
     private val cipher: CordnBlobCipher = KeyStoreCordnBlobCipher(),
     /**
@@ -696,7 +698,7 @@ class CordnRuntime(
         forget(coordinatorPubKey)
         groups.forgetCoordinator(coordinatorPubKey)
         withContext(Dispatchers.IO) {
-            CordnStorageLayout.directoryFor(filesDir, accountSigner.pubKey, coordinatorPubKey).deleteRecursively()
+            platformFileSystem.deleteRecursivelyQuietly(CordnStorageLayout.directoryFor(filesDir, accountSigner.pubKey, coordinatorPubKey))
         }
     }
 
@@ -841,7 +843,7 @@ class CordnRuntime(
             // The old state goes first. Leaving it would merge two devices'
             // histories for any gid present in both, which is the one outcome
             // this must never produce.
-            File(filesDir, "cordn/${accountSigner.pubKey}").deleteRecursively()
+            platformFileSystem.deleteRecursivelyQuietly(filesDir / "cordn" / accountSigner.pubKey)
 
             archive.groups.forEach { group ->
                 val store = FileCordnGroupStore(CordnStorageLayout.directoryFor(filesDir, accountSigner.pubKey, group.coordinatorPubKey), cipher)

amethyst/src/test/java/com/vitorpamplona/amethyst/cordn/CordnRuntimeTest.kt

@@ -59,6 +59,7 @@ import kotlinx.coroutines.cancel
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.withTimeoutOrNull
+import okio.Path.Companion.toOkioPath
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
@@ -180,7 +181,7 @@ class CordnRuntimeTest {
     ) = CordnRuntime(
         accountSigner = signer,
         client = client,
-        filesDir = root,
+        filesDir = root.toOkioPath(),
         scope = scope,
         cipher = XorCipher(),
         links = links,
@@ -443,8 +444,8 @@ class CordnRuntimeTest {
             // A gid is unique only within one coordinator, so both hold
             // "shared-gid" as unrelated groups. Deleting a level too high takes
             // both, and the only visible symptom is a room that vanished.
-            assertFalse(CordnStorageLayout.directoryFor(root, account, keyA).exists())
-            assertTrue(CordnStorageLayout.directoryFor(root, account, keyB).exists())
+            assertFalse(CordnStorageLayout.directoryFor(root.toOkioPath(), account, keyA).toFile().exists())
+            assertTrue(CordnStorageLayout.directoryFor(root.toOkioPath(), account, keyB).toFile().exists())
             assertEquals(
                 listOf(keyB),
                 runtime.groups.all.value
@@ -466,7 +467,7 @@ class CordnRuntimeTest {
                 CordnRuntime(
                     accountSigner = NostrSignerInternal(KeyPair()),
                     client = EmptyNostrClient(),
-                    filesDir = root,
+                    filesDir = root.toOkioPath(),
                     scope = runtimeScope(),
                     cipher = XorCipher(),
                     links = links,

cli/src/main/kotlin/com/vitorpamplona/amethyst/cli/CordnContext.kt

@@ -32,7 +32,8 @@ import com.vitorpamplona.amethyst.commons.cordn.KeyedCordnBlobCipher
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
-import java.io.File
+import okio.Path
+import okio.Path.Companion.toOkioPath
 
 /**
  * cordn wiring for the CLI, split out of [Context] the way [CashuContext] is
@@ -72,7 +73,7 @@ class CordnContext(
             accountPubKey = accountPubKey,
             scopes =
                 FileBackedCordnScopeFactory(
-                    root = ctx.dataDir.root,
+                    root = migrationRoot,
                     cipher = cipher,
                     links = CordnLinks.over(ctx.signer, ctx.client),
                 ),
@@ -81,7 +82,7 @@ class CordnContext(
 
     private val coordinatorStore by lazy {
         FileCordnCoordinatorStore(
-            CordnStorageLayout.accountDirectoryFor(ctx.dataDir.root, accountPubKey),
+            CordnStorageLayout.accountDirectoryFor(migrationRoot, accountPubKey),
             cipher,
         )
     }
@@ -117,8 +118,8 @@ class CordnContext(
             it.keyPackages.restore()
         }
 
-    /** Where the cordn tree lives, for the migration verbs. */
-    val migrationRoot: File get() = ctx.dataDir.root
+    /** The root the cordn tree is laid out under, for the stores and the migration verbs. */
+    val migrationRoot: Path get() = ctx.dataDir.root.toOkioPath()
 
     /** The at-rest cipher, so a migration can read and write the same blobs. */
     val blobCipher: CordnBlobCipher get() = cipher

commons/plans/2026-08-30-commons-migration-sweep.md

@@ -1773,3 +1773,29 @@ first. None of the findings below came from the move; all are on `main`.
   drops it, so a refresh only spins for a second.
 - `ScheduledFlag` still reads `TimeUtils.now()` once, so a card composed before the start
   time keeps the date after it passes.
+
+## 2026-09-28 — cordn file stores and `EncryptedAppendLog` to `commonMain`
+
+`cordn/FileCordnStores.kt` (`CordnStorageLayout` and the group, key-package,
+coordinator and handoff stores), `cordn/FileBackedCordnScopeFactory.kt`,
+`cordn/CordnMigrationStores.kt` and `storage/EncryptedAppendLog.kt` moved from
+jvmAndroid to commonMain. They take an okio `Path` plus a `FileSystem`
+(default `platformFileSystem`), the `ScheduledPostStore` shape.
+
+These files hold encrypted MLS group state that cannot be re-derived, so the
+format is pinned first: `CordnStorageFormatGoldenTest` was committed against the
+`java.io` implementation, asserting the exact tree of paths and the exact bytes
+of every file, and passes unchanged on the okio one. Notes on the port:
+
+- `ByteBuffer` framing (the cursor file) is okio `Buffer.writeLong`/`readLong`;
+  both are big-endian.
+- `java.util.Base64` in the migration snapshot is `kotlin.io.encoding.Base64.Default`
+  with `PaddingOption.PRESENT_OPTIONAL`, the same shape as the napplet move.
+- `File.delete()`/`deleteRecursively()` returned false instead of throwing, and
+  `renameTo` fell back to copy-and-delete. okio throws; the File behaviour is kept
+  by `deleteQuietly`, `deleteRecursivelyQuietly` and `moveOrCopy` in
+  `commons/util/FileSystemExt.kt`. One deliberate difference: the recursive delete
+  removes symlinks instead of following them.
+- The log's `fsync`s are `FileHandle.flush()`, which is `FileDescriptor.sync()`
+  on the JVM and Android.
+- `EncryptedMarmotMessageStore` stays in jvmAndroid and passes `toOkioPath()` to the log.

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/cordn/CordnMigrationStores.kt

@@ -20,13 +20,16 @@
  */
 package com.vitorpamplona.amethyst.commons.cordn
 
+import com.vitorpamplona.amethyst.commons.util.deleteRecursivelyQuietly
+import com.vitorpamplona.amethyst.commons.util.platformFileSystem
 import com.vitorpamplona.quartz.cordn.appMultiDevice.CordnCarriedKeyPackage
 import com.vitorpamplona.quartz.cordn.spec02Envelopes.CordnDeliveredMessageCodec
 import com.vitorpamplona.quartz.cordn.sync.GroupCursor
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
-import java.io.File
-import java.util.Base64
+import okio.FileSystem
+import okio.Path
+import kotlin.io.encoding.Base64
 
 /**
  * Reading a handoff snapshot off the cordn stores, and writing one back.
@@ -46,18 +49,19 @@ object CordnMigrationStores {
      * precisely when it matters.
      */
     suspend fun read(
-        root: File,
+        root: Path,
         accountPubKey: HexKey,
         cipher: CordnBlobCipher,
         configs: List<CoordinatorConfig>,
+        fileSystem: FileSystem = platformFileSystem,
     ): CordnMigrationSnapshot {
         val groups = mutableListOf<CordnMigrationGroup>()
         val keyPackages = mutableListOf<CordnCarriedKeyPackage>()
 
         configs.forEach { config ->
             val dir = CordnStorageLayout.directoryFor(root, accountPubKey, config.pubKey)
-            val groupStore = FileCordnGroupStore(dir, cipher)
-            val keyPackageStore = FileCordnKeyPackageStore(dir, cipher)
+            val groupStore = FileCordnGroupStore(dir, cipher, fileSystem)
+            val keyPackageStore = FileCordnKeyPackageStore(dir, cipher, fileSystem)
 
             groupStore.listGroups().forEach { gid ->
                 val state = groupStore.loadGroup(gid) ?: return@forEach
@@ -127,19 +131,20 @@ object CordnMigrationStores {
      * `gid` present in both cannot end up half from each.
      */
     suspend fun write(
-        root: File,
+        root: Path,
         accountPubKey: HexKey,
         cipher: CordnBlobCipher,
         snapshot: CordnMigrationSnapshot,
+        fileSystem: FileSystem = platformFileSystem,
     ): List<CoordinatorConfig> {
         require(snapshot.accountPubKey == accountPubKey) {
             "this migration belongs to a different account"
         }
 
-        File(root, "cordn/$accountPubKey").deleteRecursively()
+        fileSystem.deleteRecursivelyQuietly(root / "cordn" / accountPubKey)
 
         snapshot.groups.forEach { group ->
-            val store = FileCordnGroupStore(CordnStorageLayout.directoryFor(root, accountPubKey, group.coordinatorPubKey), cipher)
+            val store = FileCordnGroupStore(CordnStorageLayout.directoryFor(root, accountPubKey, group.coordinatorPubKey), cipher, fileSystem)
             store.saveGroup(group.gid, group.clientStateBase64.fromBase64())
             // Before the cursor, for the same reason the live path writes them in
             // that order: a seeding that wrote the cursor and then failed would
@@ -158,7 +163,7 @@ object CordnMigrationStores {
         }
 
         snapshot.keyPackages.forEach { keyPackage ->
-            FileCordnKeyPackageStore(CordnStorageLayout.directoryFor(root, accountPubKey, keyPackage.coordinatorPubKey), cipher)
+            FileCordnKeyPackageStore(CordnStorageLayout.directoryFor(root, accountPubKey, keyPackage.coordinatorPubKey), cipher, fileSystem)
                 .save(keyPackage.keyPackageRef, keyPackage.bundle.fromBase64())
         }
 
@@ -176,7 +181,15 @@ object CordnMigrationStores {
             }
     }
 
-    private fun ByteArray.toBase64() = Base64.getEncoder().encodeToString(this)
+    /**
+     * Standard alphabet, padded on the way out and optional on the way in,
+     * which is what `java.util.Base64`'s basic encoder and decoder did — so a
+     * snapshot written by an older build still reads, and one written here
+     * reads on an older build.
+     */
+    private val base64 = Base64.Default.withPadding(Base64.PaddingOption.PRESENT_OPTIONAL)
 
-    private fun String.fromBase64(): ByteArray = Base64.getDecoder().decode(this)
+    private fun ByteArray.toBase64() = base64.encode(this)
+
+    private fun String.fromBase64(): ByteArray = base64.decode(this)
 }

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/cordn/FileBackedCordnScopeFactory.kt

@@ -20,8 +20,10 @@
  */
 package com.vitorpamplona.amethyst.commons.cordn
 
+import com.vitorpamplona.amethyst.commons.util.platformFileSystem
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
-import java.io.File
+import okio.FileSystem
+import okio.Path
 
 /**
  * The production [CordnCoordinatorScopeFactory]: encrypted files on disk, plus
@@ -38,9 +40,10 @@ import java.io.File
  *   `<root>/cordn/<account>/<coordinator>`; see [CordnStorageLayout].
  */
 class FileBackedCordnScopeFactory(
-    private val root: File,
+    private val root: Path,
     private val cipher: CordnBlobCipher,
     private val links: CordnCoordinatorLinkFactory,
+    private val fileSystem: FileSystem = platformFileSystem,
 ) : CordnCoordinatorScopeFactory {
     override suspend fun open(
         accountPubKey: HexKey,
@@ -54,8 +57,8 @@ class FileBackedCordnScopeFactory(
 
             override suspend fun serverInfo() = link.serverInfo()
 
-            override val groupStore = FileCordnGroupStore(dir, cipher)
-            override val keyPackageStore = FileCordnKeyPackageStore(dir, cipher)
+            override val groupStore = FileCordnGroupStore(dir, cipher, fileSystem)
+            override val keyPackageStore = FileCordnKeyPackageStore(dir, cipher, fileSystem)
 
             // Only the transport closes. The files outlive the session by
             // design — closing a coordinator is not leaving its groups, and

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/cordn/FileCordnStores.kt

@@ -21,6 +21,11 @@
 package com.vitorpamplona.amethyst.commons.cordn
 
 import com.vitorpamplona.amethyst.commons.storage.EncryptedAppendLog
+import com.vitorpamplona.amethyst.commons.util.deleteQuietly
+import com.vitorpamplona.amethyst.commons.util.deleteRecursivelyQuietly
+import com.vitorpamplona.amethyst.commons.util.moveOrCopy
+import com.vitorpamplona.amethyst.commons.util.platformFileSystem
+import com.vitorpamplona.amethyst.commons.util.sibling
 import com.vitorpamplona.quartz.cordn.spec02Envelopes.CordnDeliveredMessage
 import com.vitorpamplona.quartz.cordn.spec02Envelopes.CordnDeliveredMessageCodec
 import com.vitorpamplona.quartz.cordn.sync.EchoState
@@ -28,11 +33,13 @@ import com.vitorpamplona.quartz.cordn.sync.GroupCursor
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.utils.Log
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.IO
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
-import java.io.File
-import java.nio.ByteBuffer
+import okio.Buffer
+import okio.FileSystem
+import okio.Path
 import kotlin.io.encoding.Base64
 import kotlin.io.encoding.ExperimentalEncodingApi
 
@@ -56,13 +63,13 @@ object CordnStorageLayout {
      * a caller could smuggle `..` into a directory name.
      */
     fun directoryFor(
-        root: File,
+        root: Path,
         accountPubKey: HexKey,
         coordinatorPubKey: HexKey,
-    ): File {
+    ): Path {
         require(accountPubKey.matches(HEX)) { "account pubkey must be hex" }
         require(coordinatorPubKey.matches(HEX)) { "coordinator pubkey must be hex" }
-        return File(root, "cordn/$accountPubKey/$coordinatorPubKey")
+        return root / "cordn" / accountPubKey / coordinatorPubKey
     }
 
     /**
@@ -74,11 +81,11 @@ object CordnStorageLayout {
      * make that coordinator's removal delete the record of the others.
      */
     fun accountDirectoryFor(
-        root: File,
+        root: Path,
         accountPubKey: HexKey,
-    ): File {
+    ): Path {
         require(accountPubKey.matches(HEX)) { "account pubkey must be hex" }
-        return File(root, "cordn/$accountPubKey")
+        return root / "cordn" / accountPubKey
     }
 
     /**
@@ -126,19 +133,22 @@ private const val TAG = "CordnStores"
  * is not a stale group, it is an unreadable one, and the group cannot be
  * re-derived from anywhere else on this device.
  */
-private fun atomicWrite(
-    file: File,
+private fun FileSystem.atomicWrite(
+    file: Path,
     data: ByteArray,
 ) {
-    file.parentFile?.mkdirs()
-    val temp = File(file.parentFile, "${file.name}.tmp")
-    temp.writeBytes(data)
-    if (!temp.renameTo(file)) {
-        temp.copyTo(file, overwrite = true)
-        temp.delete()
-    }
+    file.parent?.let { createDirectories(it) }
+    val temp = file.sibling("${file.name}.tmp")
+    write(temp) { write(data) }
+    moveOrCopy(temp, file)
 }
 
+private fun FileSystem.readBytes(file: Path): ByteArray = read(file) { readByteArray() }
+
+private fun FileSystem.isDirectory(path: Path): Boolean = metadataOrNull(path)?.isDirectory == true
+
+private fun FileSystem.isRegularFile(path: Path): Boolean = metadataOrNull(path)?.isRegularFile == true
+
 /**
  * A [CordnGroupStore] on the filesystem, encrypted through [cipher].
  *
@@ -158,29 +168,30 @@ private fun atomicWrite(
  * that both encrypt blobs, which is not an abstraction worth having.
  */
 class FileCordnGroupStore(
-    private val dir: File,
+    private val dir: Path,
     private val cipher: CordnBlobCipher,
+    private val fileSystem: FileSystem = platformFileSystem,
 ) : CordnGroupStore {
-    private fun groupDir(gid: String) = File(dir, "groups/${CordnStorageLayout.encodeKey(gid)}")
+    private fun groupDir(gid: String) = dir / "groups" / CordnStorageLayout.encodeKey(gid)
 
-    private fun stateFile(gid: String) = File(groupDir(gid), "state")
+    private fun stateFile(gid: String) = groupDir(gid) / "state"
 
-    private fun cursorFile(gid: String) = File(groupDir(gid), "cursor")
+    private fun cursorFile(gid: String) = groupDir(gid) / "cursor"
 
-    private fun joinOriginFile(gid: String) = File(groupDir(gid), "via-request")
+    private fun joinOriginFile(gid: String) = groupDir(gid) / "via-request"
 
-    private fun roomStateFile(gid: String) = File(groupDir(gid), "room")
+    private fun roomStateFile(gid: String) = groupDir(gid) / "room"
 
-    private fun echoStateFile(gid: String) = File(groupDir(gid), "echoes")
+    private fun echoStateFile(gid: String) = groupDir(gid) / "echoes"
 
     /**
      * Inside [groupDir] so [deleteGroup]'s recursive delete already covers it:
      * a group that left its history behind would keep the plaintext of an
      * end-to-end encrypted conversation after the key that read it was gone.
      */
-    private fun messagesFile(gid: String) = File(groupDir(gid), "messages")
+    private fun messagesFile(gid: String) = groupDir(gid) / "messages"
 
-    private fun summaryFile(gid: String) = File(groupDir(gid), "newest")
+    private fun summaryFile(gid: String) = groupDir(gid) / "newest"
 
     /**
      * Appending a segment rather than rewriting the conversation, so the cost
@@ -192,6 +203,7 @@ class FileCordnGroupStore(
             // The log treats null as "this segment is unreadable" and carries on
             // with the rest, which is what one corrupt segment should cost.
             decrypt = { runCatching { cipher.decrypt(it) }.getOrNull() },
+            fileSystem = fileSystem,
         )
 
     private val messageLock = Mutex()
@@ -217,13 +229,13 @@ class FileCordnGroupStore(
         gid: String,
         state: ByteArray,
     ) = withContext(Dispatchers.IO) {
-        atomicWrite(stateFile(gid), cipher.encrypt(state))
+        fileSystem.atomicWrite(stateFile(gid), cipher.encrypt(state))
     }
 
     override suspend fun loadGroup(gid: String): ByteArray? =
         withContext(Dispatchers.IO) {
             val file = stateFile(gid)
-            if (!file.exists()) null else cipher.decrypt(file.readBytes())
+            if (!fileSystem.exists(file)) null else cipher.decrypt(fileSystem.readBytes(file))
         }
 
     override suspend fun deleteGroup(gid: String) {
@@ -238,35 +250,39 @@ class FileCordnGroupStore(
             // The cursor goes with it. Leaving one behind would mean a later
             // re-join of the same gid resumes from a cursor belonging to a
             // group it is no longer in, skipping everything before it.
-            groupDir(gid).deleteRecursively()
+            fileSystem.deleteRecursivelyQuietly(groupDir(gid))
         }
     }
 
     override suspend fun listGroups(): List<String> =
         withContext(Dispatchers.IO) {
-            File(dir, "groups")
-                .listFiles()
+            fileSystem
+                .listOrNull(dir / "groups")
                 .orEmpty()
-                .filter { it.isDirectory && File(it, "state").exists() }
+                .filter { fileSystem.isDirectory(it) && fileSystem.exists(it / "state") }
                 .mapNotNull { CordnStorageLayout.decodeKey(it.name) }
         }
 
+    // Two big-endian int64s, which is what ByteBuffer wrote: its default order
+    // is BIG_ENDIAN, and so is okio's Buffer.
     override suspend fun saveCursor(
         gid: String,
         cursor: GroupCursor,
     ) = withContext(Dispatchers.IO) {
-        val buffer = ByteBuffer.allocate(16).putLong(cursor.fetchCursor).putLong(cursor.lastCursor)
-        atomicWrite(cursorFile(gid), cipher.encrypt(buffer.array()))
+        val bytes = Buffer().writeLong(cursor.fetchCursor).writeLong(cursor.lastCursor).readByteArray()
+        fileSystem.atomicWrite(cursorFile(gid), cipher.encrypt(bytes))
     }
 
     override suspend fun loadCursor(gid: String): GroupCursor? =
         withContext(Dispatchers.IO) {
             val file = cursorFile(gid)
-            if (!file.exists()) return@withContext null
-            val bytes = cipher.decrypt(file.readBytes())
+            if (!fileSystem.exists(file)) return@withContext null
+            val bytes = cipher.decrypt(fileSystem.readBytes(file))
             if (bytes.size < 16) return@withContext null
-            val buffer = ByteBuffer.wrap(bytes)
-            GroupCursor(fetchCursor = buffer.long, lastCursor = buffer.long)
+            // Only the first 16 bytes are read, as ByteBuffer.wrap did; a longer
+            // blob's tail is ignored rather than refused.
+            val buffer = Buffer().write(bytes, 0, 16)
+            GroupCursor(fetchCursor = buffer.readLong(), lastCursor = buffer.readLong())
         }
 
     // Existence IS the flag, so there is nothing to encrypt and nothing to
@@ -275,11 +291,11 @@ class FileCordnGroupStore(
     // later re-join of the same gid is a different admission.
     override suspend fun saveJoinedViaRequest(gid: String) {
         withContext(Dispatchers.IO) {
-            atomicWrite(joinOriginFile(gid), ByteArray(0))
+            fileSystem.atomicWrite(joinOriginFile(gid), ByteArray(0))
         }
     }
 
-    override suspend fun loadJoinedViaRequest(gid: String): Boolean = withContext(Dispatchers.IO) { joinOriginFile(gid).exists() }
+    override suspend fun loadJoinedViaRequest(gid: String): Boolean = withContext(Dispatchers.IO) { fileSystem.exists(joinOriginFile(gid)) }
 
     override suspend fun saveRoomState(
         gid: String,
@@ -288,18 +304,18 @@ class FileCordnGroupStore(
         // Deleted rather than blanked when there is nothing to remember, so an
         // emptied draft leaves no plaintext behind in an old file.
         if (state.isBlank) {
-            roomStateFile(gid).delete()
+            fileSystem.deleteQuietly(roomStateFile(gid))
             return@withContext
         }
-        atomicWrite(roomStateFile(gid), cipher.encrypt(CordnRoomStateCodec.encode(state)))
+        fileSystem.atomicWrite(roomStateFile(gid), cipher.encrypt(CordnRoomStateCodec.encode(state)))
     }
 
     override suspend fun loadRoomState(gid: String): CordnRoomState =
         withContext(Dispatchers.IO) {
             val file = roomStateFile(gid)
-            if (!file.exists()) return@withContext CordnRoomState()
+            if (!fileSystem.exists(file)) return@withContext CordnRoomState()
             try {
-                CordnRoomStateCodec.decode(cipher.decrypt(file.readBytes()))
+                CordnRoomStateCodec.decode(cipher.decrypt(fileSystem.readBytes(file)))
             } catch (e: Exception) {
                 CordnRoomState()
             }
@@ -316,12 +332,12 @@ class FileCordnGroupStore(
             // this check that makes re-delivery free rather than duplicating.
             if (!ids.add(message.envelope.id)) return@withContext
 
-            groupDir(gid).mkdirs()
+            fileSystem.createDirectories(groupDir(gid))
             messageLog.append(messagesFile(gid), CordnDeliveredMessageCodec.encode(message))
             // Written on the same beat, so the inbox preview cannot disagree
             // with the room. Whole-blob rather than appended: it is one entry
             // that is always overwritten.
-            atomicWrite(summaryFile(gid), cipher.encrypt(CordnMessageSummaryCodec.encode(message, ids.size)))
+            fileSystem.atomicWrite(summaryFile(gid), cipher.encrypt(CordnMessageSummaryCodec.encode(message, ids.size)))
         }
     }
 
@@ -337,9 +353,9 @@ class FileCordnGroupStore(
     override suspend fun loadMessageSummary(gid: String): CordnMessageSummary? =
         withContext(Dispatchers.IO) {
             val file = summaryFile(gid)
-            if (!file.exists()) return@withContext null
+            if (!fileSystem.exists(file)) return@withContext null
             try {
-                CordnMessageSummaryCodec.decode(cipher.decrypt(file.readBytes()))
+                CordnMessageSummaryCodec.decode(cipher.decrypt(fileSystem.readBytes(file)))
             } catch (e: Exception) {
                 // A summary is a derived convenience; losing one costs a preview
                 // line until the next message, not the history it summarises.
@@ -355,18 +371,18 @@ class FileCordnGroupStore(
         // Deleted when there is nothing pending, so the common steady state is
         // no file rather than an empty one.
         if (state.isEmpty) {
-            echoStateFile(gid).delete()
+            fileSystem.deleteQuietly(echoStateFile(gid))
             return@withContext
         }
-        atomicWrite(echoStateFile(gid), cipher.encrypt(EchoStateCodec.encode(state)))
+        fileSystem.atomicWrite(echoStateFile(gid), cipher.encrypt(EchoStateCodec.encode(state)))
     }
 
     override suspend fun loadEchoState(gid: String): EchoState =
         withContext(Dispatchers.IO) {
             val file = echoStateFile(gid)
-            if (!file.exists()) return@withContext EchoState()
+            if (!fileSystem.exists(file)) return@withContext EchoState()
             try {
-                EchoStateCodec.decode(cipher.decrypt(file.readBytes()))
+                EchoStateCodec.decode(cipher.decrypt(fileSystem.readBytes(file)))
             } catch (e: Exception) {
                 EchoState()
             }
@@ -385,36 +401,37 @@ class FileCordnGroupStore(
  * publishes different ones to different coordinators.
  */
 class FileCordnKeyPackageStore(
-    private val dir: File,
+    private val dir: Path,
     private val cipher: CordnBlobCipher,
+    private val fileSystem: FileSystem = platformFileSystem,
 ) : CordnKeyPackageStore {
-    private fun bundleFile(keyPackageRef: String) = File(dir, "keypackages/${CordnStorageLayout.encodeKey(keyPackageRef)}")
+    private fun bundleFile(keyPackageRef: String) = dir / "keypackages" / CordnStorageLayout.encodeKey(keyPackageRef)
 
     override suspend fun save(
         keyPackageRef: String,
         bundle: ByteArray,
     ) = withContext(Dispatchers.IO) {
-        atomicWrite(bundleFile(keyPackageRef), cipher.encrypt(bundle))
+        fileSystem.atomicWrite(bundleFile(keyPackageRef), cipher.encrypt(bundle))
     }
 
     override suspend fun load(keyPackageRef: String): ByteArray? =
         withContext(Dispatchers.IO) {
             val file = bundleFile(keyPackageRef)
-            if (!file.exists()) null else cipher.decrypt(file.readBytes())
+            if (!fileSystem.exists(file)) null else cipher.decrypt(fileSystem.readBytes(file))
         }
 
     override suspend fun delete(keyPackageRef: String) {
         withContext(Dispatchers.IO) {
-            bundleFile(keyPackageRef).delete()
+            fileSystem.deleteQuietly(bundleFile(keyPackageRef))
         }
     }
 
     override suspend fun list(): List<String> =
         withContext(Dispatchers.IO) {
-            File(dir, "keypackages")
-                .listFiles()
+            fileSystem
+                .listOrNull(dir / "keypackages")
                 .orEmpty()
-                .filter { it.isFile }
+                .filter { fileSystem.isRegularFile(it) }
                 // No explicit ".tmp" exclusion, because the encoding already
                 // is one: '.' is not in the base64url alphabet, so a temp file
                 // left behind by a crashed write cannot decode to a ref and
@@ -435,22 +452,23 @@ class FileCordnKeyPackageStore(
  * account, sitting above the per-coordinator directories it names.
  */
 class FileCordnCoordinatorStore(
-    private val dir: File,
+    private val dir: Path,
     private val cipher: CordnBlobCipher,
+    private val fileSystem: FileSystem = platformFileSystem,
 ) : CordnCoordinatorStore {
-    private val file get() = File(dir, "coordinators")
+    private val file get() = dir / "coordinators"
 
     override suspend fun save(configs: List<CoordinatorConfig>) =
         withContext(Dispatchers.IO) {
-            atomicWrite(file, cipher.encrypt(CoordinatorListCodec.encode(configs)))
+            fileSystem.atomicWrite(file, cipher.encrypt(CoordinatorListCodec.encode(configs)))
         }
 
     override suspend fun load(): List<CoordinatorConfig> =
         withContext(Dispatchers.IO) {
             val stored = file
-            if (!stored.exists()) return@withContext emptyList()
+            if (!fileSystem.exists(stored)) return@withContext emptyList()
             try {
-                CoordinatorListCodec.decode(cipher.decrypt(stored.readBytes()))
+                CoordinatorListCodec.decode(cipher.decrypt(fileSystem.readBytes(stored)))
             } catch (e: Exception) {
                 // A list written by a future build, or one the keystore can no
                 // longer decrypt. Returning nothing loses the coordinators but
@@ -463,7 +481,8 @@ class FileCordnCoordinatorStore(
                 // the rooms are gone from the inbox and the invitations screen
                 // says there is nowhere to look. One line is the difference
                 // between a diagnosable fault and a mystery.
-                Log.w(TAG, "could not read ${stored.length()} bytes of coordinators, losing them: ${e.message}", e)
+                val size = fileSystem.metadataOrNull(stored)?.size ?: 0L
+                Log.w(TAG, "could not read $size bytes of coordinators, losing them: ${e.message}", e)
                 emptyList()
             }
         }
@@ -478,19 +497,20 @@ class FileCordnCoordinatorStore(
  * groups to another one, the exact fork the flag exists to prevent.
  */
 class FileCordnHandoffStore(
-    private val accountDir: File,
+    private val accountDir: Path,
+    private val fileSystem: FileSystem = platformFileSystem,
 ) : CordnHandoffStore {
-    override suspend fun load(): Boolean = marker().exists()
+    override suspend fun load(): Boolean = fileSystem.exists(marker())
 
     override suspend fun save(handedOff: Boolean) {
         val file = marker()
         if (handedOff) {
-            file.parentFile?.mkdirs()
-            file.writeBytes(ByteArray(0))
+            file.parent?.let { fileSystem.createDirectories(it) }
+            fileSystem.write(file) { }
         } else {
-            file.delete()
+            fileSystem.deleteQuietly(file)
         }
     }
 
-    private fun marker() = File(accountDir, "handed-off")
+    private fun marker() = accountDir / "handed-off"
 }

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/storage/EncryptedAppendLog.kt

@@ -20,9 +20,12 @@
  */
 package com.vitorpamplona.amethyst.commons.storage
 
-import java.io.File
-import java.io.FileOutputStream
-import java.io.RandomAccessFile
+import com.vitorpamplona.amethyst.commons.util.moveOrCopy
+import com.vitorpamplona.amethyst.commons.util.platformFileSystem
+import com.vitorpamplona.amethyst.commons.util.sibling
+import okio.FileSystem
+import okio.Path
+import okio.use
 
 /**
  * An encrypted-at-rest log of UTF-8 entries that can be appended to in
@@ -74,11 +77,14 @@ import java.io.RandomAccessFile
  *   open. One unreadable segment then costs only its own entries; a throw would
  *   abort the whole read, and a caller that reads an empty log can overwrite a
  *   history that was merely unreadable.
+ * @param fileSystem where the logs live. Durability rests on
+ *   [okio.FileHandle.flush], which on the JVM and Android is an `fsync`.
  */
 class EncryptedAppendLog(
     private val encrypt: (ByteArray) -> ByteArray,
     private val decrypt: (ByteArray) -> ByteArray?,
     private val compactAfterSegments: Int = COMPACT_AFTER_SEGMENTS,
+    private val fileSystem: FileSystem = platformFileSystem,
 ) {
     /** Entries of one file, plus what it takes to append without re-reading it. */
     private class LogState(
@@ -94,10 +100,11 @@ class EncryptedAppendLog(
         var looseEntries: Int,
     )
 
-    private val logs = mutableMapOf<String, LogState>()
+    /** Keyed by the normalized path, so two spellings of one file share an entry. */
+    private val logs = mutableMapOf<Path, LogState>()
 
-    private fun stateFor(file: File): LogState =
-        logs.getOrPut(file.absolutePath) {
+    private fun stateFor(file: Path): LogState =
+        logs.getOrPut(file.normalized()) {
             val decoded = decodeFile(file)
 
             // A torn trailing segment is dropped from the FILE, not merely from
@@ -105,9 +112,9 @@ class EncryptedAppendLog(
             // a record that parsing always stops at, so every later append is
             // written and then never read back — the log goes silently
             // write-only, for good.
-            if (decoded.headed && decoded.validLength < file.length()) {
+            if (decoded.headed && decoded.validLength < fileLength(file)) {
                 try {
-                    RandomAccessFile(file, "rw").use { it.setLength(decoded.validLength) }
+                    fileSystem.openReadWrite(file).use { it.resize(decoded.validLength) }
                 } catch (_: Exception) {
                     // Best effort: the next fold rewrites the file wholesale and
                     // resolves it anyway.
@@ -125,17 +132,17 @@ class EncryptedAppendLog(
         }
 
     /** Every entry in [file], oldest first. */
-    fun readAll(file: File): List<String> = stateFor(file).entries.toList()
+    fun readAll(file: Path): List<String> = stateFor(file).entries.toList()
 
     /** Whether [entry] is already in [file], without reading it back from disk. */
     fun contains(
-        file: File,
+        file: Path,
         entry: String,
     ): Boolean = entry in stateFor(file).seen
 
     /** Append one entry. Constant time, apart from a periodic fold. */
     fun append(
-        file: File,
+        file: Path,
         entry: String,
     ) {
         val state = stateFor(file)
@@ -176,13 +183,13 @@ class EncryptedAppendLog(
      * between.
      */
     private fun foldLooseTail(
-        file: File,
+        file: Path,
         state: LogState,
     ) {
         if (state.looseEntries == 0) return
 
-        val prefix = ByteArray(state.foldedLength.toInt())
-        RandomAccessFile(file, "r").use { it.readFully(prefix) }
+        // Exactly foldedLength bytes, or an EOFException — what readFully did.
+        val prefix = fileSystem.read(file) { readByteArray(state.foldedLength) }
 
         val folded = encrypt(encodeEntries(state.entries.takeLast(state.looseEntries)))
         val out = ByteArray(prefix.size + 4 + folded.size)
@@ -200,26 +207,28 @@ class EncryptedAppendLog(
     }
 
     private fun appendSegment(
-        file: File,
+        file: Path,
         entries: List<String>,
     ) {
-        file.parentFile?.mkdirs()
+        file.parent?.let { fileSystem.createDirectories(it) }
         val segment = encrypt(encodeEntries(entries))
-        FileOutputStream(file, true).use { out ->
-            out.write(lengthPrefix(segment.size))
-            out.write(segment)
+        // Opened without truncating and written at its current end: an append.
+        fileSystem.openReadWrite(file).use { handle ->
+            val end = handle.size()
+            handle.write(end, lengthPrefix(segment.size), 0, 4)
+            handle.write(end + 4, segment, 0, segment.size)
             // An append that survives only in the page cache would lose a
             // message the UI has already shown as sent.
-            out.fd.sync()
+            handle.flush()
         }
     }
 
     /** Replace the whole log with [entries], as a single folded segment. */
     fun rewrite(
-        file: File,
+        file: Path,
         entries: List<String>,
     ) {
-        file.parentFile?.mkdirs()
+        file.parent?.let { fileSystem.createDirectories(it) }
 
         val segment = encrypt(encodeEntries(entries))
         val out = ByteArray(HEADER_LENGTH + 4 + segment.size)
@@ -230,7 +239,7 @@ class EncryptedAppendLog(
         atomicWrite(file, out)
 
         val state =
-            logs.getOrPut(file.absolutePath) {
+            logs.getOrPut(file.normalized()) {
                 LogState(mutableListOf(), mutableSetOf(), headed = true, foldedLength = 0L, looseSegments = 0, looseEntries = 0)
             }
         state.entries.clear()
@@ -244,8 +253,8 @@ class EncryptedAppendLog(
     }
 
     /** Drop the in-memory cache for [file]; call when the file is deleted. */
-    fun forget(file: File) {
-        logs.remove(file.absolutePath)
+    fun forget(file: Path) {
+        logs.remove(file.normalized())
     }
 
     private class Decoded(
@@ -258,11 +267,11 @@ class EncryptedAppendLog(
         val looseEntries: Int,
     )
 
-    private fun decodeFile(file: File): Decoded {
+    private fun decodeFile(file: Path): Decoded {
         // A file that does not exist yet has no header, so the first append has
         // to write one rather than tack a bare segment onto nothing.
-        if (!file.exists()) return Decoded(emptyList(), false, 0L, 0L, 0, 0)
-        val bytes = file.readBytes()
+        if (!fileSystem.exists(file)) return Decoded(emptyList(), false, 0L, 0L, 0, 0)
+        val bytes = fileSystem.read(file) { readByteArray() }
 
         if (!bytes.startsWithMagic() || bytes.size < HEADER_LENGTH) {
             // The older format: the file is one encrypted blob and nothing else.
@@ -347,20 +356,22 @@ class EncryptedAppendLog(
 
     /** Write via a temp file and rename, so a crash can't leave a half-written log. */
     private fun atomicWrite(
-        target: File,
+        target: Path,
         data: ByteArray,
     ) {
-        val tempFile = File(target.parentFile, "${target.name}.tmp")
-        FileOutputStream(tempFile).use { out ->
-            out.write(data)
-            out.fd.sync()
-        }
-        if (!tempFile.renameTo(target)) {
-            tempFile.copyTo(target, overwrite = true)
-            tempFile.delete()
+        val tempFile = target.sibling("${target.name}.tmp")
+        fileSystem.openReadWrite(tempFile).use { handle ->
+            // Truncated first, as opening a FileOutputStream did: a stale temp
+            // longer than [data] must not leave its tail behind.
+            handle.resize(0L)
+            handle.write(0L, data, 0, data.size)
+            handle.flush()
         }
+        fileSystem.moveOrCopy(tempFile, target)
     }
 
+    private fun fileLength(file: Path): Long = fileSystem.metadataOrNull(file)?.size ?: 0L
+
     private fun ByteArray.startsWithMagic(): Boolean {
         if (size < MAGIC.size) return false
         for (i in MAGIC.indices) if (this[i] != MAGIC[i]) return false

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/util/FileSystemExt.kt

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.util
+
+import okio.FileSystem
+import okio.IOException
+import okio.Path
+import okio.Path.Companion.toPath
+
+/*
+ * The java.io.File idioms that okio spells differently, for stores moving off
+ * File without changing what they do on failure.
+ *
+ * okio reports a failed delete or rename by throwing; File reported it by
+ * returning false, and the stores were written around that. These keep the
+ * File behaviour, so a port is a port and not a quiet change in error handling.
+ */
+
+/** A file next to this one: `File(parentFile, name)`. */
+fun Path.sibling(name: String): Path = parent?.div(name) ?: name.toPath()
+
+/**
+ * Deletes a file or an empty directory, and never throws: `File.delete()`.
+ *
+ * @return true when [path] is gone, including when it never existed.
+ */
+fun FileSystem.deleteQuietly(path: Path): Boolean =
+    try {
+        delete(path)
+        true
+    } catch (e: IOException) {
+        !exists(path)
+    }
+
+/**
+ * Deletes [path] and everything under it, carrying on past anything it cannot
+ * delete: `File.deleteRecursively()`.
+ *
+ * One difference, deliberately kept: symlinks are deleted, never followed.
+ * `File.deleteRecursively` walks into a linked directory and empties it, which
+ * no store here ever wanted.
+ *
+ * @return true when nothing is left, including when [path] never existed.
+ */
+fun FileSystem.deleteRecursivelyQuietly(path: Path): Boolean {
+    // Directories come before their children in this listing, so the reverse
+    // deletes every child before the directory holding it.
+    val children =
+        try {
+            listRecursively(path).toList()
+        } catch (e: IOException) {
+            emptyList()
+        }
+    var deleted = true
+    for (child in children.asReversed()) deleted = deleteQuietly(child) && deleted
+    return deleteQuietly(path) && deleted
+}
+
+/**
+ * Replaces [target] with [source]: an atomic rename, or, where the filesystem
+ * refuses one, a copy over [target] and a delete of [source].
+ *
+ * The fallback is what `if (!temp.renameTo(file)) { temp.copyTo(file, true); temp.delete() }`
+ * did. It is not atomic, and is only here so that a filesystem without rename
+ * still gets written.
+ */
+fun FileSystem.moveOrCopy(
+    source: Path,
+    target: Path,
+) {
+    try {
+        atomicMove(source, target)
+    } catch (e: IOException) {
+        copy(source, target)
+        deleteQuietly(source)
+    }
+}

commons/src/jvmAndroid/kotlin/com/vitorpamplona/amethyst/commons/marmot/EncryptedMarmotMessageStore.kt

@@ -29,6 +29,7 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
+import okio.Path.Companion.toOkioPath
 import java.io.File
 
 /**
@@ -72,13 +73,13 @@ class EncryptedMarmotMessageStore(
         logMutex.withLock {
             try {
                 val file = messagesFile(nostrGroupId)
-                if (log.contains(file, innerEventJson)) {
+                if (log.contains(file.toOkioPath(), innerEventJson)) {
                     Log.d(TAG) { "appendMessage($nostrGroupId): duplicate entry skipped" }
                     return@withLock
                 }
-                log.append(file, innerEventJson)
+                log.append(file.toOkioPath(), innerEventJson)
                 Log.d(TAG) {
-                    "appendMessage($nostrGroupId): now ${log.readAll(file).size} message(s) persisted"
+                    "appendMessage($nostrGroupId): now ${log.readAll(file.toOkioPath()).size} message(s) persisted"
                 }
             } catch (e: Exception) {
                 Log.e(TAG, "appendMessage($nostrGroupId) FAILED: ${e.message}", e)
@@ -105,7 +106,7 @@ class EncryptedMarmotMessageStore(
         withContext(Dispatchers.IO) {
             logMutex.withLock {
                 for (file in listOf(messagesFile(nostrGroupId), epochsFile(nostrGroupId), snapshotFile(nostrGroupId), expiriesFile(nostrGroupId), epochRetentionsFile(nostrGroupId))) {
-                    log.forget(file)
+                    log.forget(file.toOkioPath())
                     if (file.exists() && !file.delete()) {
                         Log.w(TAG) { "delete($nostrGroupId): failed to remove ${file.absolutePath}" }
                     }
@@ -340,7 +341,7 @@ class EncryptedMarmotMessageStore(
 
     private fun readAll(nostrGroupId: String): List<String> = readAllFrom(messagesFile(nostrGroupId))
 
-    private fun readAllFrom(file: File): List<String> = log.readAll(file)
+    private fun readAllFrom(file: File): List<String> = log.readAll(file.toOkioPath())
 
     private fun writeAll(
         nostrGroupId: String,
@@ -350,7 +351,7 @@ class EncryptedMarmotMessageStore(
     private fun writeAllTo(
         file: File,
         messages: List<String>,
-    ) = log.rewrite(file, messages)
+    ) = log.rewrite(file.toOkioPath(), messages)
 
     companion object {
         private const val TAG = "EncryptedMarmotMessageStore"

commons/src/jvmTest/kotlin/com/vitorpamplona/amethyst/commons/cordn/CordnHandoffStateTest.kt

@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.commons.cordn
 
 import kotlinx.coroutines.test.runTest
+import okio.Path.Companion.toOkioPath
 import org.junit.Assert.assertFalse
 import org.junit.Assert.assertThrows
 import org.junit.Assert.assertTrue
@@ -106,5 +107,5 @@ class CordnHandoffStateTest {
             assertTrue(first.handedOff.value)
         }
 
-    private fun state() = CordnHandoffState(FileCordnHandoffStore(folder.root))
+    private fun state() = CordnHandoffState(FileCordnHandoffStore(folder.root.toOkioPath()))
 }

commons/src/jvmTest/kotlin/com/vitorpamplona/amethyst/commons/cordn/CordnMigrationStoresBase64Test.kt

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.cordn
+
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
+import kotlinx.coroutines.test.runTest
+import okio.Path.Companion.toOkioPath
+import java.util.Base64
+import kotlin.io.path.createTempDirectory
+import kotlin.random.Random
+import kotlin.test.AfterTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * A handoff snapshot's base64 must mean the same thing on both sides of an
+ * upgrade: a phone on an older build (which used `java.util.Base64`) hands off
+ * to one on this build, and the other way round.
+ *
+ * Every length mod 3, so every padding case, and each input both padded and
+ * unpadded, because `java.util.Base64.getDecoder()` accepted either.
+ */
+class CordnMigrationStoresBase64Test {
+    private object Identity : CordnBlobCipher {
+        override fun encrypt(bytes: ByteArray) = bytes
+
+        override fun decrypt(bytes: ByteArray) = bytes
+    }
+
+    private val rootFile = createTempDirectory("cordn-b64").toFile()
+    private val root = rootFile.toOkioPath()
+    private val account = "e".repeat(64)
+    private val coordinator = "b".repeat(64)
+
+    @AfterTest
+    fun cleanUp() {
+        rootFile.deleteRecursively()
+    }
+
+    @Test
+    fun `snapshot base64 is java util Base64 in both directions`() =
+        runTest {
+            val random = Random(7)
+            val blobs = (1..13).map { random.nextBytes(it) }
+            val javaEncoder = Base64.getEncoder()
+            val unpadded = Base64.getEncoder().withoutPadding()
+
+            val snapshot =
+                CordnMigrationSnapshot(
+                    accountPubKey = account,
+                    groups =
+                        blobs.mapIndexed { i, blob ->
+                            CordnMigrationGroup(
+                                coordinatorPubKey = coordinator,
+                                coordinatorRelays = listOf("wss://coord.example"),
+                                gid = "g" + i.toString().padStart(2, '0'),
+                                clientStateBase64 = if (i % 2 == 0) javaEncoder.encodeToString(blob) else unpadded.encodeToString(blob),
+                                cursor = 0,
+                            )
+                        },
+                )
+
+            CordnMigrationStores.write(root, account, Identity, snapshot)
+            val read =
+                CordnMigrationStores.read(
+                    root,
+                    account,
+                    Identity,
+                    listOf(CoordinatorConfig(coordinator, listOf(RelayUrlNormalizer.normalizeOrNull("wss://coord.example")!!))),
+                )
+
+            assertEquals(
+                blobs.map { javaEncoder.encodeToString(it) },
+                read.groups.sortedBy { it.gid }.map { it.clientStateBase64 },
+            )
+        }
+}

commons/src/jvmTest/kotlin/com/vitorpamplona/amethyst/commons/cordn/CordnStorageFormatGoldenTest.kt

@@ -31,6 +31,7 @@ import com.vitorpamplona.quartz.cordn.sync.PendingEpochOperation
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.RelayUrlNormalizer
 import kotlinx.coroutines.test.runTest
+import okio.Path.Companion.toOkioPath
 import java.io.ByteArrayOutputStream
 import java.io.File
 import java.util.Base64
@@ -92,13 +93,15 @@ class CordnStorageFormatGoldenTest {
 
     // ---- Construction glue: the only part of this file that follows the stores' API. ----
 
-    private fun groupStore(coordinator: HexKey) = FileCordnGroupStore(CordnStorageLayout.directoryFor(rootFile, account, coordinator), cipher)
+    private val root = rootFile.toOkioPath()
 
-    private fun keyPackageStore(coordinator: HexKey) = FileCordnKeyPackageStore(CordnStorageLayout.directoryFor(rootFile, account, coordinator), cipher)
+    private fun groupStore(coordinator: HexKey) = FileCordnGroupStore(CordnStorageLayout.directoryFor(root, account, coordinator), cipher)
 
-    private fun coordinatorStore() = FileCordnCoordinatorStore(CordnStorageLayout.accountDirectoryFor(rootFile, account), cipher)
+    private fun keyPackageStore(coordinator: HexKey) = FileCordnKeyPackageStore(CordnStorageLayout.directoryFor(root, account, coordinator), cipher)
 
-    private fun handoffStore(owner: HexKey) = FileCordnHandoffStore(CordnStorageLayout.accountDirectoryFor(rootFile, owner))
+    private fun coordinatorStore() = FileCordnCoordinatorStore(CordnStorageLayout.accountDirectoryFor(root, account), cipher)
+
+    private fun handoffStore(owner: HexKey) = FileCordnHandoffStore(CordnStorageLayout.accountDirectoryFor(root, owner))
 
     private fun appendLog(compactAfterSegments: Int) =
         EncryptedAppendLog(
@@ -107,11 +110,11 @@ class CordnStorageFormatGoldenTest {
             compactAfterSegments = compactAfterSegments,
         )
 
-    private fun logFile(name: String) = File(rootFile, "logs/$name")
+    private fun logFile(name: String) = root / "logs" / name
 
-    private suspend fun migrationWrite(snapshot: CordnMigrationSnapshot) = CordnMigrationStores.write(rootFile, migratedAccount, cipher, snapshot)
+    private suspend fun migrationWrite(snapshot: CordnMigrationSnapshot) = CordnMigrationStores.write(root, migratedAccount, cipher, snapshot)
 
-    private suspend fun migrationRead(configs: List<CoordinatorConfig>) = CordnMigrationStores.read(rootFile, migratedAccount, cipher, configs)
+    private suspend fun migrationRead(configs: List<CoordinatorConfig>) = CordnMigrationStores.read(root, migratedAccount, cipher, configs)
 
     // ---- End of construction glue. ----
 

commons/src/jvmTest/kotlin/com/vitorpamplona/amethyst/commons/cordn/FileCordnStoresTest.kt

@@ -27,6 +27,7 @@ import kotlinx.coroutines.async
 import kotlinx.coroutines.awaitAll
 import kotlinx.coroutines.test.runTest
 import kotlinx.coroutines.withContext
+import okio.Path.Companion.toOkioPath
 import java.io.File
 import kotlin.test.AfterTest
 import kotlin.test.Test
@@ -70,16 +71,17 @@ class FileCordnStoresTest {
             it.delete()
             it.mkdirs()
         }
+    private val rootPath = root.toOkioPath()
     private val cipher = XorCipher()
 
     private val account = "a".repeat(64)
     private val coordinator = "b".repeat(64)
 
-    private fun dir() = CordnStorageLayout.directoryFor(root, account, coordinator)
+    private fun dir() = CordnStorageLayout.directoryFor(rootPath, account, coordinator)
 
     private fun groups() = FileCordnGroupStore(dir(), cipher)
 
-    private fun coordinators() = FileCordnCoordinatorStore(CordnStorageLayout.accountDirectoryFor(root, account), cipher)
+    private fun coordinators() = FileCordnCoordinatorStore(CordnStorageLayout.accountDirectoryFor(rootPath, account), cipher)
 
     private fun relay(url: String) = RelayUrlNormalizer.normalizeOrNull(url)!!
 
@@ -110,7 +112,12 @@ class FileCordnStoresTest {
             val state = "ratchet-tree-and-epoch-secrets".encodeToByteArray()
             groups().saveGroup("g1", state)
 
-            val onDisk = dir().walkTopDown().filter { it.isFile }.toList()
+            val onDisk =
+                dir()
+                    .toFile()
+                    .walkTopDown()
+                    .filter { it.isFile }
+                    .toList()
             assertTrue(onDisk.isNotEmpty(), "nothing was written at all")
             onDisk.forEach {
                 val raw = it.readBytes()
@@ -138,7 +145,7 @@ class FileCordnStoresTest {
 
             val escaped = File(root, "cordn/etc").exists() || File(root.parentFile, "etc").exists()
             assertTrue(!escaped, "the write escaped the store directory")
-            assertTrue(dir().walkTopDown().any { it.isFile }, "it was not written anywhere at all")
+            assertTrue(dir().toFile().walkTopDown().any { it.isFile }, "it was not written anywhere at all")
         }
 
     @Test
@@ -159,7 +166,7 @@ class FileCordnStoresTest {
         runTest {
             // The rule the layout exists for. Two coordinators can both serve
             // gid "shared" as unrelated groups with different ratchet trees.
-            val other = CordnStorageLayout.directoryFor(root, account, "c".repeat(64))
+            val other = CordnStorageLayout.directoryFor(rootPath, account, "c".repeat(64))
             FileCordnGroupStore(dir(), cipher).saveGroup("shared", byteArrayOf(1))
             FileCordnGroupStore(other, cipher).saveGroup("shared", byteArrayOf(2))
 
@@ -170,7 +177,7 @@ class FileCordnStoresTest {
     @Test
     fun `two accounts on one device do not see each other`() =
         runTest {
-            val theirs = CordnStorageLayout.directoryFor(root, "d".repeat(64), coordinator)
+            val theirs = CordnStorageLayout.directoryFor(rootPath, "d".repeat(64), coordinator)
             groups().saveGroup("g1", byteArrayOf(1))
 
             assertTrue(FileCordnGroupStore(theirs, cipher).listGroups().isEmpty())
@@ -179,8 +186,8 @@ class FileCordnStoresTest {
 
     @Test
     fun `a non-hex pubkey never becomes a directory`() {
-        assertFailsWith<IllegalArgumentException> { CordnStorageLayout.directoryFor(root, "../escape", coordinator) }
-        assertFailsWith<IllegalArgumentException> { CordnStorageLayout.directoryFor(root, account, "../escape") }
+        assertFailsWith<IllegalArgumentException> { CordnStorageLayout.directoryFor(rootPath, "../escape", coordinator) }
+        assertFailsWith<IllegalArgumentException> { CordnStorageLayout.directoryFor(rootPath, account, "../escape") }
     }
 
     @Test
@@ -248,7 +255,7 @@ class FileCordnStoresTest {
             // encoding — swap it for something that passes names through and
             // this fails, which is the regression worth catching.
             keyPackages().save("ref1", byteArrayOf(1))
-            File(dir(), "keypackages/${CordnStorageLayout.encodeKey("ref2")}.tmp").writeBytes(byteArrayOf(2))
+            File(dir().toFile(), "keypackages/${CordnStorageLayout.encodeKey("ref2")}.tmp").writeBytes(byteArrayOf(2))
 
             assertEquals(listOf("ref1"), keyPackages().list())
         }
@@ -259,8 +266,8 @@ class FileCordnStoresTest {
             // Ignoring one unreadable name is better than failing the listing
             // and hiding every real group behind it.
             groups().saveGroup("g1", byteArrayOf(1))
-            File(dir(), "groups/not-base64-@@@").mkdirs()
-            File(dir(), "groups/not-base64-@@@/state").writeBytes(byteArrayOf(0))
+            File(dir().toFile(), "groups/not-base64-@@@").mkdirs()
+            File(dir().toFile(), "groups/not-base64-@@@/state").writeBytes(byteArrayOf(0))
 
             assertEquals(listOf("g1"), groups().listGroups())
         }
@@ -298,7 +305,7 @@ class FileCordnStoresTest {
 
             assertContentEquals(byteArrayOf(2, 2), store.loadGroup("g1"))
             assertTrue(
-                dir().walkTopDown().none { it.name.endsWith(".tmp") },
+                dir().toFile().walkTopDown().none { it.name.endsWith(".tmp") },
                 "a temp file survived the rename",
             )
         }
@@ -314,7 +321,7 @@ class FileCordnStoresTest {
             coordinators().save(configs)
 
             assertEquals(configs, coordinators().load())
-            val onDisk = File(CordnStorageLayout.accountDirectoryFor(root, account), "coordinators").readBytes()
+            val onDisk = File(CordnStorageLayout.accountDirectoryFor(rootPath, account).toFile(), "coordinators").readBytes()
             assertFalse(onDisk.decodeToString().contains(coordinator), "the pubkey went to disk in the clear")
         }
 
@@ -340,7 +347,7 @@ class FileCordnStoresTest {
     fun `an unreadable list loses the coordinators rather than the login`() =
         runTest {
             coordinators().save(listOf(CoordinatorConfig(coordinator, listOf(relay("wss://one.example.com")))))
-            File(CordnStorageLayout.accountDirectoryFor(root, account), "coordinators").writeBytes(byteArrayOf(9, 9, 9))
+            File(CordnStorageLayout.accountDirectoryFor(rootPath, account).toFile(), "coordinators").writeBytes(byteArrayOf(9, 9, 9))
 
             assertEquals(emptyList(), coordinators().load())
         }
@@ -350,8 +357,8 @@ class FileCordnStoresTest {
         runTest {
             // If it lived inside a coordinator's own directory, removing that
             // coordinator would delete the record of every other one with it.
-            val listFile = File(CordnStorageLayout.accountDirectoryFor(root, account), "coordinators")
-            assertEquals(dir().parentFile, listFile.parentFile)
+            val listFile = File(CordnStorageLayout.accountDirectoryFor(rootPath, account).toFile(), "coordinators")
+            assertEquals(dir().toFile().parentFile, listFile.parentFile)
         }
 
     @Test
@@ -363,15 +370,15 @@ class FileCordnStoresTest {
             // same gid and deleting a level too high takes both.
             val other = "e".repeat(64)
             groups().saveGroup("shared-gid", byteArrayOf(1, 2, 3))
-            FileCordnGroupStore(CordnStorageLayout.directoryFor(root, account, other), cipher)
+            FileCordnGroupStore(CordnStorageLayout.directoryFor(rootPath, account, other), cipher)
                 .saveGroup("shared-gid", byteArrayOf(4, 5, 6))
 
-            CordnStorageLayout.directoryFor(root, account, coordinator).deleteRecursively()
+            CordnStorageLayout.directoryFor(rootPath, account, coordinator).toFile().deleteRecursively()
 
             assertNull(groups().loadGroup("shared-gid"))
             assertContentEquals(
                 byteArrayOf(4, 5, 6),
-                FileCordnGroupStore(CordnStorageLayout.directoryFor(root, account, other), cipher).loadGroup("shared-gid"),
+                FileCordnGroupStore(CordnStorageLayout.directoryFor(rootPath, account, other), cipher).loadGroup("shared-gid"),
             )
         }
 
@@ -385,7 +392,7 @@ class FileCordnStoresTest {
             coordinators().save(listOf(CoordinatorConfig(coordinator, listOf(relay("wss://one.example.com")))))
             groups().saveGroup("gid", byteArrayOf(1))
 
-            CordnStorageLayout.directoryFor(root, account, coordinator).deleteRecursively()
+            CordnStorageLayout.directoryFor(rootPath, account, coordinator).toFile().deleteRecursively()
 
             assertEquals(1, coordinators().load().size)
         }
@@ -415,7 +422,7 @@ class FileCordnStoresTest {
             store.saveRoomState("gid", CordnRoomState(draft = "the secret plan", lastReadCursor = 7))
 
             assertEquals(CordnRoomState("the secret plan", 7), store.loadRoomState("gid"))
-            val onDisk = File(dir(), "groups/${CordnStorageLayout.encodeKey("gid")}/room").readBytes()
+            val onDisk = File(dir().toFile(), "groups/${CordnStorageLayout.encodeKey("gid")}/room").readBytes()
             assertFalse(onDisk.decodeToString().contains("the secret plan"), "a draft went to disk in the clear")
         }
 
@@ -430,7 +437,7 @@ class FileCordnStoresTest {
             store.saveRoomState("gid", CordnRoomState(draft = "typed"))
             store.saveRoomState("gid", CordnRoomState())
 
-            assertFalse(File(dir(), "groups/${CordnStorageLayout.encodeKey("gid")}/room").exists())
+            assertFalse(File(dir().toFile(), "groups/${CordnStorageLayout.encodeKey("gid")}/room").exists())
             assertEquals(CordnRoomState(), store.loadRoomState("gid"))
         }
 
@@ -440,7 +447,7 @@ class FileCordnStoresTest {
             val store = groups()
             store.saveGroup("gid", byteArrayOf(1))
             store.saveRoomState("gid", CordnRoomState(draft = "typed", lastReadCursor = 3))
-            File(dir(), "groups/${CordnStorageLayout.encodeKey("gid")}/room").writeBytes(byteArrayOf(7, 7, 7))
+            File(dir().toFile(), "groups/${CordnStorageLayout.encodeKey("gid")}/room").writeBytes(byteArrayOf(7, 7, 7))
 
             assertEquals(CordnRoomState(), store.loadRoomState("gid"))
             assertNotNull(store.loadGroup("gid"))

commons/src/jvmTest/kotlin/com/vitorpamplona/amethyst/commons/storage/EncryptedAppendLogTest.kt

@@ -20,6 +20,7 @@
  */
 package com.vitorpamplona.amethyst.commons.storage
 
+import okio.Path.Companion.toOkioPath
 import java.io.File
 import java.nio.file.Files
 import kotlin.test.Test
@@ -61,39 +62,39 @@ class EncryptedAppendLogTest {
     fun `entries survive a round trip through a fresh reader`() {
         val file = tempFile()
         val writer = cipher()
-        writer.append(file, "first")
-        writer.append(file, "second")
-        writer.append(file, "third")
+        writer.append(file.toOkioPath(), "first")
+        writer.append(file.toOkioPath(), "second")
+        writer.append(file.toOkioPath(), "third")
 
         // A second instance reads only what reached the disk.
-        assertContentEquals(listOf("first", "second", "third"), cipher().readAll(file))
+        assertContentEquals(listOf("first", "second", "third"), cipher().readAll(file.toOkioPath()))
     }
 
     @Test
     fun `an empty log reads as empty rather than failing`() {
-        assertContentEquals(emptyList(), cipher().readAll(tempFile()))
+        assertContentEquals(emptyList(), cipher().readAll(tempFile().toOkioPath()))
     }
 
     @Test
     fun `contains answers without reading the file back`() {
         val file = tempFile()
         val log = cipher()
-        log.append(file, "hello")
+        log.append(file.toOkioPath(), "hello")
 
-        assertTrue(log.contains(file, "hello"))
-        assertFalse(log.contains(file, "goodbye"))
+        assertTrue(log.contains(file.toOkioPath(), "hello"))
+        assertFalse(log.contains(file.toOkioPath(), "goodbye"))
     }
 
     @Test
     fun `a rewrite replaces the whole log`() {
         val file = tempFile()
         val log = cipher()
-        log.append(file, "a")
-        log.append(file, "b")
-        log.rewrite(file, listOf("b"))
+        log.append(file.toOkioPath(), "a")
+        log.append(file.toOkioPath(), "b")
+        log.rewrite(file.toOkioPath(), listOf("b"))
 
-        assertContentEquals(listOf("b"), cipher().readAll(file))
-        assertFalse(cipher().contains(file, "a"))
+        assertContentEquals(listOf("b"), cipher().readAll(file.toOkioPath()))
+        assertFalse(cipher().contains(file.toOkioPath(), "a"))
     }
 
     @Test
@@ -101,9 +102,9 @@ class EncryptedAppendLogTest {
         val file = tempFile()
         val log = cipher(compactAfter = 4)
         val written = (1..20).map { "entry-$it" }
-        written.forEach { log.append(file, it) }
+        written.forEach { log.append(file.toOkioPath(), it) }
 
-        assertContentEquals(written, cipher().readAll(file))
+        assertContentEquals(written, cipher().readAll(file.toOkioPath()))
         // Folding every four appends leaves ~5 segments rather than 20, which is
         // the bound on read cost that matters here.
         assertTrue(file.length() < 20 * SEGMENT_OVERHEAD_CEILING, "log should have been compacted, was ${file.length()} bytes")
@@ -116,10 +117,10 @@ class EncryptedAppendLogTest {
 
         // The first append lays the header down; the next four are the loose run
         // that the fourth of them collapses.
-        (1..5).forEach { log.append(file, "first-run-$it") }
+        (1..5).forEach { log.append(file.toOkioPath(), "first-run-$it") }
         val afterFirstFold = file.readBytes()
 
-        (1..4).forEach { log.append(file, "second-run-$it") }
+        (1..4).forEach { log.append(file.toOkioPath(), "second-run-$it") }
         val afterSecondFold = file.readBytes()
 
         // The SEGMENTS the first fold produced must survive verbatim. If they
@@ -135,7 +136,7 @@ class EncryptedAppendLogTest {
             afterSecondFold.copyOfRange(HEADER_LEN, afterFirstFold.size).toList(),
             "folding the tail must copy the already-folded segments as ciphertext",
         )
-        assertContentEquals((1..5).map { "first-run-$it" } + (1..4).map { "second-run-$it" }, cipher().readAll(file))
+        assertContentEquals((1..5).map { "first-run-$it" } + (1..4).map { "second-run-$it" }, cipher().readAll(file.toOkioPath()))
     }
 
     @Test
@@ -145,7 +146,7 @@ class EncryptedAppendLogTest {
         // Exactly what the old writer produced: one encrypted blob, no magic.
         file.writeBytes(legacyBlob(listOf("old-one", "old-two")))
 
-        assertContentEquals(listOf("old-one", "old-two"), cipher().readAll(file))
+        assertContentEquals(listOf("old-one", "old-two"), cipher().readAll(file.toOkioPath()))
     }
 
     @Test
@@ -155,9 +156,9 @@ class EncryptedAppendLogTest {
         file.writeBytes(legacyBlob(listOf("old-one", "old-two")))
 
         val log = cipher()
-        log.append(file, "new-one")
+        log.append(file.toOkioPath(), "new-one")
 
-        assertContentEquals(listOf("old-one", "old-two", "new-one"), cipher().readAll(file))
+        assertContentEquals(listOf("old-one", "old-two", "new-one"), cipher().readAll(file.toOkioPath()))
         // and the upgraded file is in the new format, so the next append is cheap
         assertTrue(file.readBytes().decodeToString().startsWith("MRMTLOG3"))
     }
@@ -166,31 +167,31 @@ class EncryptedAppendLogTest {
     fun `a torn final append costs only the torn entry`() {
         val file = tempFile()
         val log = cipher()
-        log.append(file, "kept-one")
-        log.append(file, "kept-two")
+        log.append(file.toOkioPath(), "kept-one")
+        log.append(file.toOkioPath(), "kept-two")
 
         // Simulate process death partway through writing the third segment.
         val intact = file.readBytes()
-        log.append(file, "lost")
+        log.append(file.toOkioPath(), "lost")
         val torn = file.readBytes()
         file.writeBytes(torn.copyOfRange(0, intact.size + 6))
 
-        assertContentEquals(listOf("kept-one", "kept-two"), cipher().readAll(file))
+        assertContentEquals(listOf("kept-one", "kept-two"), cipher().readAll(file.toOkioPath()))
     }
 
     @Test
     fun `a segment that cannot be decrypted does not hide the rest`() {
         val file = tempFile()
         val log = cipher()
-        log.append(file, "before")
-        log.append(file, "after")
+        log.append(file.toOkioPath(), "before")
+        log.append(file.toOkioPath(), "after")
 
         // Corrupt the first segment's nonce marker so decrypt returns null for it.
         val bytes = file.readBytes()
         bytes[HEADER_LEN + 4] = 0
         file.writeBytes(bytes)
 
-        assertContentEquals(listOf("after"), cipher().readAll(file))
+        assertContentEquals(listOf("after"), cipher().readAll(file.toOkioPath()))
     }
 
     @Test
@@ -201,21 +202,21 @@ class EncryptedAppendLogTest {
         // writes and never read one back again — silently write-only, for good.
         val file = tempFile()
         val log = cipher()
-        log.append(file, "kept-one")
-        log.append(file, "kept-two")
+        log.append(file.toOkioPath(), "kept-one")
+        log.append(file.toOkioPath(), "kept-two")
 
         val intact = file.readBytes()
-        log.append(file, "lost")
+        log.append(file.toOkioPath(), "lost")
         val torn = file.readBytes()
         file.writeBytes(torn.copyOfRange(0, intact.size + 6))
 
         val reopened = cipher()
-        assertContentEquals(listOf("kept-one", "kept-two"), reopened.readAll(file))
+        assertContentEquals(listOf("kept-one", "kept-two"), reopened.readAll(file.toOkioPath()))
 
-        reopened.append(file, "three")
+        reopened.append(file.toOkioPath(), "three")
         assertContentEquals(
             listOf("kept-one", "kept-two", "three"),
-            cipher().readAll(file),
+            cipher().readAll(file.toOkioPath()),
             "an append after a torn tail must be readable by the next reader",
         )
     }
@@ -230,11 +231,11 @@ class EncryptedAppendLogTest {
         repeat(12) { session ->
             // A fresh instance per session, as a cold process gets.
             val log = cipher(compactAfter = 4)
-            repeat(3) { log.append(file, "s$session-m$it") }
+            repeat(3) { log.append(file.toOkioPath(), "s$session-m$it") }
         }
 
         val expected = (0 until 12).flatMap { session -> (0 until 3).map { "s$session-m$it" } }
-        assertContentEquals(expected, cipher().readAll(file))
+        assertContentEquals(expected, cipher().readAll(file.toOkioPath()))
 
         // 36 entries at a fold every 4 appends: a handful of segments, not 36.
         assertTrue(
@@ -256,8 +257,8 @@ class EncryptedAppendLogTest {
                 decrypt = { null },
             )
 
-        runCatching { log.append(file, "never-written") }
-        assertFalse(log.contains(file, "never-written"), "a write that failed must not count as persisted")
+        runCatching { log.append(file.toOkioPath(), "never-written") }
+        assertFalse(log.contains(file.toOkioPath(), "never-written"), "a write that failed must not count as persisted")
     }
 
     @Test
@@ -265,9 +266,9 @@ class EncryptedAppendLogTest {
         val file = tempFile()
         val log = cipher()
         val awkward = listOf("", "emoji 👩‍👧 here", "a\nb\tc", "\"quoted\": {\"json\": 1}")
-        awkward.forEach { log.append(file, it) }
+        awkward.forEach { log.append(file.toOkioPath(), it) }
 
-        assertEquals(awkward, cipher().readAll(file))
+        assertEquals(awkward, cipher().readAll(file.toOkioPath()))
     }
 
     /** The pre-segment on-disk shape: `encrypt(uint32 count, (uint32 len, bytes)*)`. */