diff --git a/app/src/androidTest/kotlin/org/libremail/data/local/DatabaseEncryptionProbeInstrumentedTest.kt b/app/src/androidTest/kotlin/org/libremail/data/local/DatabaseEncryptionProbeInstrumentedTest.kt
new file mode 100644
index 0000000..955049a
--- /dev/null
+++ b/app/src/androidTest/kotlin/org/libremail/data/local/DatabaseEncryptionProbeInstrumentedTest.kt
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+package org.libremail.data.local
+
+import android.content.Context
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import org.junit.After
+import org.junit.Assert.assertFalse
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import java.io.File
+
+/**
+ * On-device cover for the issue-#359 keyed-open probe ([DatabaseEncryption.probeKeyedOpen]). The probe
+ * is the fix for gap 2: it reaches the REAL `SQLiteConnection.nativeOpen` — the exact #359 crash site —
+ * from inside `DatabaseProvisioner`'s fail-closed handler, so an open-time `UnsatisfiedLinkError` on an
+ * incompatible device is caught and converted to `CacheEncryptionUnavailableException` before Room's
+ * later deferred open can crash on it uncaught.
+ *
+ * This runs the real SQLCipher native path (mocked out of the JVM unit tests), asserting two things a
+ * device is needed for: on a compatible device the probe opens+closes the keyed database WITHOUT
+ * throwing, and — on every device — it leaves no file behind (it opens a throwaway sibling, never the
+ * real cache, and cleans up its sidecars). All data is synthetic; nothing here is PII.
+ */
+@RunWith(AndroidJUnit4::class)
+class DatabaseEncryptionProbeInstrumentedTest {
+
+    private val context = ApplicationProvider.getApplicationContext<Context>()
+    private val cacheName = "probe_test_cache.db"
+    private val cacheFile: File get() = context.getDatabasePath(cacheName)
+
+    // 64 hex chars == a 32-byte SQLCipher passphrase, matching DatabaseKeyStore's format.
+    private val passphrase = "0123456789abcdef".repeat(4)
+
+    @Before
+    @After
+    fun clean() {
+        cacheFile.parentFile
+            ?.listFiles { f -> f.name.startsWith(cacheName) }
+            ?.forEach { it.delete() }
+    }
+
+    @Test
+    fun probeKeyedOpen_reachesNativeOpen_thenLeavesNoFileBehind() {
+        // The provisioner loads the native library immediately before probing (probeKeyedOpen's
+        // precondition, kept out of the probe so the load happens exactly once per open); mirror that here.
+        DatabaseEncryption.ensureNativeLibraryLoaded()
+        // On a compatible device this returns normally (keyed nativeOpen succeeds); on an incompatible one
+        // it throws UnsatisfiedLinkError here — the exact #359 signature the provisioner now fails closed
+        // on. Either way, no probe file may survive.
+        DatabaseEncryption.probeKeyedOpen(cacheFile, passphrase)
+
+        val dir = cacheFile.parentFile!!
+        listOf("", "-wal", "-shm", "-journal").forEach { suffix ->
+            assertFalse(
+                "probe left a '$cacheName.openprobe$suffix' file behind",
+                File(dir, "$cacheName.openprobe$suffix").exists(),
+            )
+        }
+        // The probe uses a throwaway sibling, so it must never create the real cache file.
+        assertFalse("probe must not create the real cache file", cacheFile.exists())
+    }
+}
diff --git a/app/src/main/kotlin/org/libremail/data/local/CacheEncryptionUnavailableException.kt b/app/src/main/kotlin/org/libremail/data/local/CacheEncryptionUnavailableException.kt
index a73a30a..8bc4c8b 100644
--- a/app/src/main/kotlin/org/libremail/data/local/CacheEncryptionUnavailableException.kt
+++ b/app/src/main/kotlin/org/libremail/data/local/CacheEncryptionUnavailableException.kt
@@ -22,3 +22,19 @@ class CacheEncryptionUnavailableException(cause: Throwable) :
         "Encrypted cache unavailable: the SQLCipher native library failed to load on this device",
         cause,
     )
+
+/**
+ * True when this throwable (or anything in its cause chain) signals that SQLCipher's native library is
+ * unavailable on this device (issue #359): a [CacheEncryptionUnavailableException] the provisioner raised
+ * when it failed closed, or — defensively — a bare [LinkageError] (an open-time `UnsatisfiedLinkError` at
+ * `SQLiteConnection.nativeOpen` that reached a headless entry point before the provisioner wrapped it).
+ *
+ * Headless entry points that inject the Room cache directly — the WorkManager workers and `IdleService` —
+ * have no UI gate (that is `CacheEncryptionGate`'s job), so they consult this to treat such a failure as a
+ * soft defer/skip (a worker retries; the push service stops) instead of crashing. A later launch may load
+ * the library and recover, so deferring rather than failing hard is correct. The whole cause chain is
+ * walked because coroutine stack-trace recovery can re-wrap the throwable as it crosses the database-open
+ * boundary (the same reason [DatabaseProvisioner]'s own tests assert on the cause chain, not the instance).
+ */
+fun Throwable.isCacheEncryptionUnavailable(): Boolean = generateSequence(this) { it.cause }
+    .any { it is CacheEncryptionUnavailableException || it is LinkageError }
diff --git a/app/src/main/kotlin/org/libremail/data/local/DatabaseEncryption.kt b/app/src/main/kotlin/org/libremail/data/local/DatabaseEncryption.kt
index 7122f26..3ede05f 100644
--- a/app/src/main/kotlin/org/libremail/data/local/DatabaseEncryption.kt
+++ b/app/src/main/kotlin/org/libremail/data/local/DatabaseEncryption.kt
@@ -115,8 +115,45 @@ object DatabaseEncryption {
         }
     }
 
+    /**
+     * Opens a throwaway keyed SQLCipher database next to [cacheFile] and immediately closes it, purely to
+     * reach `SQLiteConnection.nativeOpen` — the exact call site of the #359 crash — from inside
+     * [DatabaseProvisioner]'s fail-closed handler. [ensureNativeLibraryLoaded]
+     * (`System.loadLibrary("sqlcipher")`) can succeed on a device whose bundled `.so` is otherwise
+     * incompatible, yet the JNI-bound `nativeOpen` still be unresolved; that only surfaces when a keyed
+     * database is actually opened, which Room does LATER via its deferred open helper
+     * ([org.libremail.di.DatabaseModule]) — outside any handler. Probing the real open here lets the
+     * provisioner catch that [LinkageError] and fail closed BEFORE Room reaches it.
+     *
+     * Deliberately opens a sibling throwaway file (never the real cache) so it can never create, mutate,
+     * or leave `-wal`/`-shm` sidecars on the cache, then deletes the probe and its sidecars in a `finally`.
+     * Mirrors `SqlCipherOpenSpikeTest`'s stage-B keyed-open probe (issue #359).
+     *
+     * PRECONDITION: the caller must have already loaded the native library (via [ensureNativeLibraryLoaded]).
+     * The sole production caller — [DatabaseProvisioner]'s encrypted branch — does so on the line above its
+     * probe call. Kept out of here on purpose so the provisioner loads the library exactly ONCE per open
+     * (the `ensureNativeLibraryLoaded()`-exactly-once invariant its instrumented tests pin), not twice.
+     */
+    fun probeKeyedOpen(cacheFile: File, passphrase: String) {
+        val dir = cacheFile.parentFile ?: error("cache database file has no parent directory")
+        val probe = File(dir, cacheFile.name + PROBE_SUFFIX)
+        try {
+            SQLiteDatabase.openOrCreateDatabase(
+                probe.absolutePath,
+                passphrase.toByteArray(Charsets.US_ASCII),
+                null, // no CursorFactory
+                null, // no DatabaseErrorHandler
+            ).close()
+        } finally {
+            listOf("", "-wal", "-shm", "-journal").forEach { File(dir, probe.name + it).delete() }
+        }
+    }
+
     private const val TAG = "LibreMailDbCrypto"
 
+    // Suffix of the throwaway file [probeKeyedOpen] opens to reach nativeOpen without touching the cache.
+    private const val PROBE_SUFFIX = ".openprobe"
+
     // The 16-byte magic that opens every plaintext SQLite file: "SQLite format 3" + a NUL terminator.
     // Spelled out as bytes to keep the trailing NUL unambiguous.
     private val SQLITE_HEADER = byteArrayOf(
diff --git a/app/src/main/kotlin/org/libremail/data/local/DatabaseProvisioner.kt b/app/src/main/kotlin/org/libremail/data/local/DatabaseProvisioner.kt
index e301c02..409e3eb 100644
--- a/app/src/main/kotlin/org/libremail/data/local/DatabaseProvisioner.kt
+++ b/app/src/main/kotlin/org/libremail/data/local/DatabaseProvisioner.kt
@@ -104,35 +104,45 @@ class DatabaseProvisioner internal constructor(
             keyStore.clearClearPending()
         }
 
-        // One-time move of accounts/credentials/settings/signatures into the non-auth AccountDatabase
-        // (issue #111). MUST run before the cache opens: opening it applies MIGRATION_15_16, which drops
-        // the moved tables. Runs AFTER the wipe above so an unrecoverable-key cache is gone first
-        // (nothing left to move) and we never block waiting on a passphrase we can't get.
-        accountDataMigrator.migrateIfNeeded()
-
-        // Opt-in at-rest encryption of the local cache (off by default). The conversion runs here —
-        // before the database is opened — so it never races an open connection; toggling the setting
-        // therefore takes effect on the next app start. The passphrase source is resolved from which
-        // seal actually exists (DatabaseKeyStore.resolvePassphrase), NOT from the app-lock setting (a
-        // separate DataStore that can disagree). When app-lock is ON the sealing key is auth-bound, so
-        // resolvePassphrase waits on PassphraseSession until the user authenticates — which is why this
-        // must never run on the main thread while the cache is locked (issue #93).
-        val settings = settingsRepository.settings.first()
+        // FAIL CLOSED (issue #359, security rework of #367). SQLCipher's native library can fail to LOAD
+        // (UnsatisfiedLinkError from ensureNativeLibraryLoaded) OR to LINK (the library loads, but the
+        // JNI-bound SQLiteConnection.nativeOpen is unresolved and throws only when a keyed database is
+        // actually opened — the exact #359 signature). EVERY startup step that touches that library must
+        // therefore run inside this ONE handler, so any such LinkageError becomes a single fail-closed
+        // signal rather than escaping as a raw crash. On that signal we deliberately do NOT silently
+        // degrade to an unencrypted cache (that would defeat the user's opt-in encryption): we never open
+        // plaintext, wipe the on-disk ciphertext, or write the encryptCache setting — we raise a distinct
+        // exception the startup UI (CacheEncryptionGate) catches to show the encryption error gate. It is
+        // NOT memoized (a throw skips prepareCache's `.also { prepared = it }`), so the next launch
+        // re-attempts and recovers automatically if the library later loads.
+        //
+        // The catch stays typed LinkageError ONLY. It must NOT be broadened to Exception/Throwable: the
+        // migrator below deliberately throws a NON-linkage error ("crash-loop rather than lose data") on
+        // an unexpected copy failure, and that — like any other non-linkage error — must still propagate
+        // uncaught so we never drop the not-yet-copied source tables.
         return try {
+            // One-time move of accounts/credentials/settings/signatures into the non-auth AccountDatabase
+            // (issue #111). MUST run before the cache opens: opening it applies MIGRATION_15_16, which drops
+            // the moved tables. Runs AFTER the wipe above so an unrecoverable-key cache is gone first
+            // (nothing left to move) and we never block waiting on a passphrase we can't get. Runs INSIDE
+            // this handler (issue #359 gap 1): its copyAccountTables loads SQLCipher and does a keyed
+            // openOrCreateDatabase + ATTACH … KEY (a real nativeOpen) even when encryption is OFF, so a
+            // LinkageError there used to escape this handler entirely and crash-loop.
+            accountDataMigrator.migrateIfNeeded()
+
+            // Opt-in at-rest encryption of the local cache (off by default). The conversion runs here —
+            // before the database is opened — so it never races an open connection; toggling the setting
+            // therefore takes effect on the next app start. The passphrase source is resolved from which
+            // seal actually exists (DatabaseKeyStore.resolvePassphrase), NOT from the app-lock setting (a
+            // separate DataStore that can disagree). When app-lock is ON the sealing key is auth-bound, so
+            // resolvePassphrase waits on PassphraseSession until the user authenticates — which is why this
+            // must never run on the main thread while the cache is locked (issue #93).
+            val settings = settingsRepository.settings.first()
             resolveOpenMode(settings, dbFile)
         } catch (nativeLoadFailure: LinkageError) {
-            // FAIL CLOSED (issue #359, security rework of #367). SQLCipher's native library could not be
-            // loaded/linked (e.g. UnsatisfiedLinkError at SQLiteConnection.nativeOpen or from
-            // ensureNativeLibraryLoaded), so the encrypted cache cannot be opened OR converted. We must
-            // NOT silently degrade to an unencrypted cache (that would defeat the user's opt-in
-            // encryption), so we deliberately do NOT: open plaintext, wipe the on-disk ciphertext, or
-            // write the encryptCache setting. Instead raise a distinct signal the startup UI catches to
-            // show the encryption error gate. This throw is NOT memoized (it skips prepareCache's
-            // `.also { prepared = it }`), so the next launch re-attempts and recovers automatically if
-            // the library later loads.
             AppLog.w(
                 TAG,
-                "SQLCipher native library failed to load; failing closed (encrypted cache unavailable)",
+                "SQLCipher native library failed to load or link; failing closed (encrypted cache unavailable)",
                 nativeLoadFailure,
             )
             throw CacheEncryptionUnavailableException(nativeLoadFailure)
@@ -159,6 +169,13 @@ class DatabaseProvisioner internal constructor(
                 // load the keyed open reaches SQLiteConnection.nativeOpen with no library loaded and
                 // crashes with UnsatisfiedLinkError on every cold start once encryption is enabled.
                 DatabaseEncryption.ensureNativeLibraryLoaded()
+                // Probe the REAL keyed open HERE (issue #359 gap 2), inside the fail-closed handler.
+                // ensureNativeLibraryLoaded() above only loads the .so; the keyed nativeOpen that can still
+                // throw on an incompatible device fires LATER, in DatabaseModule's DeferredOpenHelperFactory
+                // AFTER prepareCache() returns — outside any handler — so an open-time UnsatisfiedLinkError
+                // there would escape uncaught. Reaching a keyed nativeOpen now converts that LinkageError to
+                // CacheEncryptionUnavailableException before Room's deferred open can crash on it.
+                DatabaseEncryption.probeKeyedOpen(dbFile, passphrase)
                 CacheOpenMode.Encrypted(passphrase)
             }
 
diff --git a/app/src/main/kotlin/org/libremail/data/sync/BackfillWorker.kt b/app/src/main/kotlin/org/libremail/data/sync/BackfillWorker.kt
index d35402a..8a5ea04 100644
--- a/app/src/main/kotlin/org/libremail/data/sync/BackfillWorker.kt
+++ b/app/src/main/kotlin/org/libremail/data/sync/BackfillWorker.kt
@@ -10,6 +10,7 @@ import dagger.assisted.Assisted
 import dagger.assisted.AssistedInject
 import kotlinx.coroutines.CancellationException
 import org.libremail.BuildConfig
+import org.libremail.data.local.isCacheEncryptionUnavailable
 import org.libremail.data.security.EncryptedCacheGuard
 import org.libremail.reporting.AppLog
 
@@ -60,7 +61,14 @@ class BackfillWorker @AssistedInject constructor(
             },
             onFailure = { error ->
                 if (error is CancellationException) throw error
-                AppLog.w(TAG, "backfill worker: retry", error)
+                // A DB open that fails because SQLCipher's native library is unavailable (issue #359) lands
+                // here (thrown inside the runCatching above); log it distinctly but still defer softly — a
+                // later launch may load the library and recover — instead of a generic retry.
+                if (error.isCacheEncryptionUnavailable()) {
+                    AppLog.w(TAG, "backfill deferred: encrypted cache unavailable (SQLCipher native library)", error)
+                } else {
+                    AppLog.w(TAG, "backfill worker: retry", error)
+                }
                 Result.retry()
             },
         )
diff --git a/app/src/main/kotlin/org/libremail/data/sync/EncryptedCacheWorkerGuard.kt b/app/src/main/kotlin/org/libremail/data/sync/EncryptedCacheWorkerGuard.kt
new file mode 100644
index 0000000..5d8164f
--- /dev/null
+++ b/app/src/main/kotlin/org/libremail/data/sync/EncryptedCacheWorkerGuard.kt
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+package org.libremail.data.sync
+
+import androidx.work.ListenableWorker.Result
+import org.libremail.data.local.isCacheEncryptionUnavailable
+import org.libremail.reporting.AppLog
+
+/**
+ * Runs [block] and, if opening the Room cache fails because SQLCipher's native library is unavailable on
+ * this device (issue #359 — a `CacheEncryptionUnavailableException` the provisioner raised, or defensively
+ * a bare `LinkageError` at `nativeOpen`), logs a PII-free breadcrumb under [tag] and returns
+ * [Result.retry] rather than letting the failure crash the worker. WorkManager workers inject the cache
+ * directly, with no UI gate; a later launch may load the library and recover, so a soft retry — not a hard
+ * failure — is correct. Every other throwable (including `CancellationException`) propagates unchanged.
+ *
+ * `inline` so the (suspending) [block] runs in the worker's own coroutine context, mirroring `runCatching`.
+ */
+internal inline fun retryIfEncryptedCacheUnavailable(tag: String, block: () -> Result): Result = try {
+    block()
+} catch (failure: Throwable) {
+    if (!failure.isCacheEncryptionUnavailable()) throw failure
+    AppLog.w(tag, "deferred: encrypted cache unavailable (SQLCipher native library)", failure)
+    Result.retry()
+}
diff --git a/app/src/main/kotlin/org/libremail/data/sync/PruneWorker.kt b/app/src/main/kotlin/org/libremail/data/sync/PruneWorker.kt
index 003c9c4..93b76c6 100644
--- a/app/src/main/kotlin/org/libremail/data/sync/PruneWorker.kt
+++ b/app/src/main/kotlin/org/libremail/data/sync/PruneWorker.kt
@@ -8,6 +8,7 @@ import androidx.work.WorkerParameters
 import dagger.Lazy
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedInject
+import org.libremail.data.local.isCacheEncryptionUnavailable
 import org.libremail.data.security.EncryptedCacheGuard
 import org.libremail.reporting.AppLog
 
@@ -39,7 +40,14 @@ class PruneWorker @AssistedInject constructor(
                 Result.success()
             },
             onFailure = { error ->
-                AppLog.w(TAG, "prune worker: retry", error)
+                // A DB open that fails because SQLCipher's native library is unavailable (issue #359) lands
+                // here (it is thrown inside the runCatching above); log it distinctly but still defer softly
+                // — a later launch may load the library and recover — instead of a generic retry.
+                if (error.isCacheEncryptionUnavailable()) {
+                    AppLog.w(TAG, "prune deferred: encrypted cache unavailable (SQLCipher native library)", error)
+                } else {
+                    AppLog.w(TAG, "prune worker: retry", error)
+                }
                 Result.retry()
             },
         )
diff --git a/app/src/main/kotlin/org/libremail/data/sync/SendWorker.kt b/app/src/main/kotlin/org/libremail/data/sync/SendWorker.kt
index 4bade40..7e18f0a 100644
--- a/app/src/main/kotlin/org/libremail/data/sync/SendWorker.kt
+++ b/app/src/main/kotlin/org/libremail/data/sync/SendWorker.kt
@@ -52,6 +52,13 @@ class SendWorker @AssistedInject constructor(
 
     override suspend fun doWork(): Result {
         if (cacheGuard.isCacheLocked()) return Result.retry()
+        // Resolving the Lazy DB deps below opens the Room cache; if SQLCipher's native library is
+        // unavailable on this device (issue #359) that open throws — with no UI gate here, treat it as a
+        // soft retry rather than letting it crash the worker.
+        return retryIfEncryptedCacheUnavailable(TAG) { drainOutbox() }
+    }
+
+    private suspend fun drainOutbox(): Result {
         val outboxDao = this.outboxDao.get()
         val accountDao = this.accountDao.get()
         val connectionFactory = this.connectionFactory.get()
diff --git a/app/src/main/kotlin/org/libremail/data/sync/SyncWorker.kt b/app/src/main/kotlin/org/libremail/data/sync/SyncWorker.kt
index 987162c..0f5e2f0 100644
--- a/app/src/main/kotlin/org/libremail/data/sync/SyncWorker.kt
+++ b/app/src/main/kotlin/org/libremail/data/sync/SyncWorker.kt
@@ -28,16 +28,21 @@ class SyncWorker @AssistedInject constructor(
             AppLog.i(TAG, "sync deferred: cache locked")
             return Result.retry()
         }
-        return mailSyncer.get().syncAll().fold(
-            onSuccess = {
-                AppLog.i(TAG, "sync worker: success")
-                Result.success()
-            },
-            onFailure = { error ->
-                AppLog.w(TAG, "sync worker: retry", error)
-                Result.retry()
-            },
-        )
+        // syncAll()'s first DB access (and thus Room's deferred cache open) can throw if SQLCipher's
+        // native library is unavailable on this device (issue #359) — that open fires OUTSIDE syncAll's own
+        // runCatching, so without this guard it would escape doWork. Treat it as a soft retry, not a crash.
+        return retryIfEncryptedCacheUnavailable(TAG) {
+            mailSyncer.get().syncAll().fold(
+                onSuccess = {
+                    AppLog.i(TAG, "sync worker: success")
+                    Result.success()
+                },
+                onFailure = { error ->
+                    AppLog.w(TAG, "sync worker: retry", error)
+                    Result.retry()
+                },
+            )
+        }
     }
 
     private companion object {
diff --git a/app/src/main/kotlin/org/libremail/push/IdleService.kt b/app/src/main/kotlin/org/libremail/push/IdleService.kt
index 6120467..f2f3722 100644
--- a/app/src/main/kotlin/org/libremail/push/IdleService.kt
+++ b/app/src/main/kotlin/org/libremail/push/IdleService.kt
@@ -27,6 +27,7 @@ import kotlinx.coroutines.isActive
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withTimeoutOrNull
 import org.libremail.data.local.dao.AccountDao
+import org.libremail.data.local.isCacheEncryptionUnavailable
 import org.libremail.data.local.toDomain
 import org.libremail.data.security.EncryptedCacheGuard
 import org.libremail.data.sync.MailConnectionFactory
@@ -110,7 +111,20 @@ class IdleService : Service() {
                 stopSelf()
                 return@launch
             }
-            reconcileWatchers()
+            // Headless tolerance for issue #359: this service injects the Room cache with NO UI gate
+            // (CacheEncryptionGate wraps only MainActivity), so if SQLCipher's native library is unavailable
+            // on this device reconcileWatchers()'s first DB access throws — a CacheEncryptionUnavailableException
+            // from the provisioner, or defensively a bare LinkageError at nativeOpen. Left uncaught, a child of
+            // this SupervisorJob would route it to the app's default handler and crash the process. Treat it
+            // like the cache-locked case: log PII-free and stop. The app's CacheEncryptionGate surfaces the
+            // error to the user, and a later restart re-probes and recovers if the library loads.
+            try {
+                reconcileWatchers()
+            } catch (unavailable: Throwable) {
+                if (!unavailable.isCacheEncryptionUnavailable()) throw unavailable
+                AppLog.w(TAG, "encrypted cache unavailable (SQLCipher native lib); deferring IDLE push", unavailable)
+                stopSelf()
+            }
         }
         // The reuse cache (issue #357 Part 2) keeps interactive/sync IMAP connections warm; sweep
         // them so a socket that has gone idle past the reuse timeout is closed rather than left
diff --git a/app/src/test/kotlin/org/libremail/data/local/CacheEncryptionUnavailableExceptionTest.kt b/app/src/test/kotlin/org/libremail/data/local/CacheEncryptionUnavailableExceptionTest.kt
new file mode 100644
index 0000000..9307a8c
--- /dev/null
+++ b/app/src/test/kotlin/org/libremail/data/local/CacheEncryptionUnavailableExceptionTest.kt
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+package org.libremail.data.local
+
+import kotlinx.coroutines.CancellationException
+import org.junit.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+/**
+ * [isCacheEncryptionUnavailable] is the shared classifier the headless entry points (WorkManager workers
+ * and `IdleService`) use to decide whether a database-open failure is the issue-#359 "SQLCipher native
+ * library unavailable" condition — which they defer/skip softly — versus any other failure, which they
+ * handle normally. It must recognise the provisioner's [CacheEncryptionUnavailableException] AND a bare
+ * [LinkageError] (defensive), even when wrapped several layers deep (coroutine stack-trace recovery
+ * re-wraps the throwable across the open boundary), and reject everything else — including
+ * [CancellationException], which must always propagate.
+ */
+class CacheEncryptionUnavailableExceptionTest {
+
+    @Test
+    fun `recognises a direct CacheEncryptionUnavailableException`() {
+        val failure = CacheEncryptionUnavailableException(UnsatisfiedLinkError("nativeOpen"))
+        assertTrue(failure.isCacheEncryptionUnavailable())
+    }
+
+    @Test
+    fun `recognises a bare LinkageError`() {
+        assertTrue(UnsatisfiedLinkError("SQLiteConnection.nativeOpen").isCacheEncryptionUnavailable())
+    }
+
+    @Test
+    fun `recognises a CacheEncryptionUnavailableException wrapped deep in the cause chain`() {
+        val wrapped = RuntimeException(
+            "room open failed",
+            IllegalStateException("delegate", CacheEncryptionUnavailableException(UnsatisfiedLinkError())),
+        )
+        assertTrue(wrapped.isCacheEncryptionUnavailable())
+    }
+
+    @Test
+    fun `recognises a LinkageError nested as a cause`() {
+        assertTrue(RuntimeException("open", UnsatisfiedLinkError("nativeOpen")).isCacheEncryptionUnavailable())
+    }
+
+    @Test
+    fun `rejects an unrelated exception`() {
+        assertFalse(IllegalStateException("database is locked").isCacheEncryptionUnavailable())
+    }
+
+    @Test
+    fun `rejects a CancellationException so cancellation still propagates`() {
+        assertFalse(CancellationException("job cancelled").isCacheEncryptionUnavailable())
+    }
+}
diff --git a/app/src/test/kotlin/org/libremail/data/local/DatabaseProvisionerTest.kt b/app/src/test/kotlin/org/libremail/data/local/DatabaseProvisionerTest.kt
index 7695bb4..3844381 100644
--- a/app/src/test/kotlin/org/libremail/data/local/DatabaseProvisionerTest.kt
+++ b/app/src/test/kotlin/org/libremail/data/local/DatabaseProvisionerTest.kt
@@ -71,6 +71,7 @@ class DatabaseProvisionerTest {
         every { DatabaseEncryption.ensureEncrypted(any(), any()) } just Runs
         every { DatabaseEncryption.ensurePlaintext(any(), any()) } just Runs
         every { DatabaseEncryption.ensureNativeLibraryLoaded() } just Runs
+        every { DatabaseEncryption.probeKeyedOpen(any(), any()) } just Runs
         every { settingsRepository.settings } returns flowOf(AppSettings())
 
         coEvery { keyStore.isClearPending() } returns false
@@ -104,6 +105,10 @@ class DatabaseProvisionerTest {
         // load only rode on that conversion, Room's keyed open would hit nativeOpen with no .so loaded
         // and throw UnsatisfiedLinkError on every cold start.
         verify(exactly = 1) { DatabaseEncryption.ensureNativeLibraryLoaded() }
+        // Issue #359 gap 2: the encrypted branch also probes a REAL keyed open (nativeOpen) inside the
+        // fail-closed handler, so an open-time UnsatisfiedLinkError is caught here rather than escaping
+        // Room's later deferred open.
+        verify(exactly = 1) { DatabaseEncryption.probeKeyedOpen(any(), PASSPHRASE) }
     }
 
     @Test
@@ -147,6 +152,53 @@ class DatabaseProvisionerTest {
         coVerify(exactly = 0) { settingsRepository.setEncryptCache(any()) }
     }
 
+    @Test
+    fun `a native-library load failure in the account migrator fails closed`() = runTest {
+        // Issue #359 gap 1 (PRIMARY): AccountDataMigrator.copyAccountTables loads SQLCipher and does a
+        // keyed openOrCreateDatabase + ATTACH … KEY (a real nativeOpen) even when encryption is OFF, so a
+        // LinkageError there must fail closed too. It used to ESCAPE the handler because migrateIfNeeded()
+        // ran OUTSIDE the try/catch (crash-loop). Un-mock the `just Runs` default (which hid the gap) and
+        // make the migrator throw the exact #359 error — encryption stays at its default OFF here to prove
+        // the migrator drags EVERY upgrader through the native library regardless of the setting.
+        coEvery { accountDataMigrator.migrateIfNeeded() } throws
+            UnsatisfiedLinkError("dlopen failed: libsqlcipher.so is not 16 KB aligned")
+
+        val error = assertFailsWith<CacheEncryptionUnavailableException> { provisioner().prepareCache() }
+
+        assertTrue(
+            generateSequence(error.cause) { it.cause }.any { it is LinkageError },
+            "the native-load LinkageError must be preserved as the cause, not surface as a raw LinkageError",
+        )
+        // Fail CLOSED, not open: nothing wiped, no seal reset, the setting untouched.
+        verify(exactly = 0) { DatabaseFiles.clear(any()) }
+        coVerify(exactly = 0) { keyStore.resetSealedPassphrase() }
+        coVerify(exactly = 0) { settingsRepository.setEncryptCache(any()) }
+    }
+
+    @Test
+    fun `a nativeOpen failure while probing the encrypted open fails closed`() = runTest {
+        every { settingsRepository.settings } returns flowOf(AppSettings(encryptCache = true, appLock = false))
+        // Issue #359 gap 2 (SECONDARY): loadLibrary succeeds, but the REAL keyed open throws an
+        // UnsatisfiedLinkError at SQLiteConnection.nativeOpen — the exact #359 signature. The provisioner
+        // probes that open INSIDE the fail-closed handler, so it converts here rather than letting Room's
+        // later deferred open (DatabaseModule) crash uncaught.
+        every { DatabaseEncryption.probeKeyedOpen(any(), any()) } throws
+            UnsatisfiedLinkError("SQLiteConnection.nativeOpen")
+
+        val error = assertFailsWith<CacheEncryptionUnavailableException> { provisioner().prepareCache() }
+
+        assertTrue(
+            generateSequence(error.cause) { it.cause }.any { it is LinkageError },
+            "the nativeOpen LinkageError must be preserved as the cause",
+        )
+        // The library loaded fine (loadLibrary was not the failure); it was the keyed nativeOpen probe.
+        verify(exactly = 1) { DatabaseEncryption.ensureNativeLibraryLoaded() }
+        verify(exactly = 1) { DatabaseEncryption.probeKeyedOpen(any(), PASSPHRASE) }
+        // No fail-open side effects.
+        verify(exactly = 0) { DatabaseFiles.clear(any()) }
+        coVerify(exactly = 0) { keyStore.resetSealedPassphrase() }
+    }
+
     @Test
     fun `a native-library load failure is not memoized and retries on the next open`() = runTest {
         every { settingsRepository.settings } returns flowOf(AppSettings(encryptCache = true, appLock = false))
@@ -237,8 +289,10 @@ class DatabaseProvisionerTest {
         verify(exactly = 0) { DatabaseEncryption.ensureEncrypted(any(), any()) }
         verify(exactly = 0) { DatabaseEncryption.ensurePlaintext(any(), any()) }
         // A plaintext cache opens with the framework helper, never SQLCipher, so it must not touch the
-        // native library — the counterpart to the encrypted path's mandatory load above.
+        // native library — the counterpart to the encrypted path's mandatory load above — nor probe a
+        // keyed open (issue #359: the probe belongs to the encrypted branch only).
         verify(exactly = 0) { DatabaseEncryption.ensureNativeLibraryLoaded() }
+        verify(exactly = 0) { DatabaseEncryption.probeKeyedOpen(any(), any()) }
     }
 
     @Test
diff --git a/app/src/test/kotlin/org/libremail/data/sync/BackfillWorkerTest.kt b/app/src/test/kotlin/org/libremail/data/sync/BackfillWorkerTest.kt
index 0550f6c..8652c05 100644
--- a/app/src/test/kotlin/org/libremail/data/sync/BackfillWorkerTest.kt
+++ b/app/src/test/kotlin/org/libremail/data/sync/BackfillWorkerTest.kt
@@ -15,6 +15,7 @@ import kotlinx.coroutines.test.runTest
 import org.junit.After
 import org.junit.Before
 import org.junit.Test
+import org.libremail.data.local.CacheEncryptionUnavailableException
 import org.libremail.data.security.EncryptedCacheGuard
 import org.libremail.reporting.AppLog
 import org.libremail.reporting.RingLogBuffer
@@ -86,6 +87,22 @@ class BackfillWorkerTest {
         assertEquals(Result.retry(), worker().doWork())
     }
 
+    @Test
+    fun `defers with a retry and a distinct breadcrumb when the encrypted cache is unavailable`() = runTest {
+        // Issue #359: the DB open fails because SQLCipher's native library is unavailable. It lands in the
+        // worker's runCatching (thrown inside runBackfill()), so it retries — but it must now log a DISTINCT
+        // breadcrumb (not the generic retry, and not mistaken for a cancellation) and still never crash.
+        coEvery { cacheGuard.isCacheLocked() } returns false
+        coEvery { backfiller.runBackfill(any()) } throws
+            CacheEncryptionUnavailableException(UnsatisfiedLinkError("SQLiteConnection.nativeOpen"))
+
+        assertEquals(Result.retry(), worker().doWork())
+
+        val entry = logBuffer.snapshot().single()
+        assertEquals('W', entry.level)
+        assertTrue(entry.message.startsWith("backfill deferred: encrypted cache unavailable"), entry.message)
+    }
+
     // --- issue #329: AppLog breadcrumbs ---------------------------------------------------------
 
     @Test
diff --git a/app/src/test/kotlin/org/libremail/data/sync/PruneWorkerTest.kt b/app/src/test/kotlin/org/libremail/data/sync/PruneWorkerTest.kt
index 45fc95d..e91c9db 100644
--- a/app/src/test/kotlin/org/libremail/data/sync/PruneWorkerTest.kt
+++ b/app/src/test/kotlin/org/libremail/data/sync/PruneWorkerTest.kt
@@ -15,6 +15,7 @@ import kotlinx.coroutines.test.runTest
 import org.junit.After
 import org.junit.Before
 import org.junit.Test
+import org.libremail.data.local.CacheEncryptionUnavailableException
 import org.libremail.data.security.EncryptedCacheGuard
 import org.libremail.reporting.AppLog
 import org.libremail.reporting.RingLogBuffer
@@ -84,6 +85,23 @@ class PruneWorkerTest {
         assertEquals(Result.retry(), worker().doWork())
     }
 
+    @Test
+    fun `defers with a retry and a distinct breadcrumb when the encrypted cache is unavailable`() = runTest {
+        // Issue #359: the DB open fails because SQLCipher's native library is unavailable. It lands in the
+        // worker's runCatching (thrown inside prune()), so it already retried — but it must now log a
+        // DISTINCT breadcrumb so a debug report shows "encrypted cache unavailable" rather than a generic
+        // retry, and still never crash.
+        coEvery { cacheGuard.isCacheLocked() } returns false
+        coEvery { pruner.prune(any()) } throws
+            CacheEncryptionUnavailableException(UnsatisfiedLinkError("SQLiteConnection.nativeOpen"))
+
+        assertEquals(Result.retry(), worker().doWork())
+
+        val entry = logBuffer.snapshot().single()
+        assertEquals('W', entry.level)
+        assertTrue(entry.message.startsWith("prune deferred: encrypted cache unavailable"), entry.message)
+    }
+
     // --- issue #329: AppLog breadcrumbs ---------------------------------------------------------
 
     @Test
diff --git a/app/src/test/kotlin/org/libremail/data/sync/SendWorkerTest.kt b/app/src/test/kotlin/org/libremail/data/sync/SendWorkerTest.kt
index 1326337..a272323 100644
--- a/app/src/test/kotlin/org/libremail/data/sync/SendWorkerTest.kt
+++ b/app/src/test/kotlin/org/libremail/data/sync/SendWorkerTest.kt
@@ -19,6 +19,7 @@ import org.junit.After
 import org.junit.Before
 import org.junit.Test
 import org.libremail.data.attachment.AttachmentUriGrants
+import org.libremail.data.local.CacheEncryptionUnavailableException
 import org.libremail.data.local.dao.AccountDao
 import org.libremail.data.local.dao.OutboxDao
 import org.libremail.data.local.entity.AccountEntity
@@ -139,6 +140,21 @@ class SendWorkerTest {
         verify(exactly = 0) { lazyGrants.get() }
     }
 
+    @Test
+    fun `defers with a retry when the encrypted cache is unavailable, without crashing`() = runTest {
+        // Cache unlocked (setUp), so the worker resolves its Lazy DB deps and reads the outbox; that first
+        // DB access (Room's deferred cache open) throws because SQLCipher's native library is unavailable
+        // on this device (issue #359). It is OUTSIDE any per-message runCatching, so without the guard it
+        // would escape doWork — the guard turns it into a soft retry with a PII-free breadcrumb.
+        coEvery { outboxDao.getAll() } throws
+            CacheEncryptionUnavailableException(UnsatisfiedLinkError("SQLiteConnection.nativeOpen"))
+
+        assertEquals(Result.retry(), worker().doWork())
+
+        val messages = logBuffer.snapshot().map { it.message }
+        assertTrue(messages.any { it.startsWith("deferred: encrypted cache unavailable") }, "messages=$messages")
+    }
+
     @Test
     fun `an empty outbox succeeds without sending`() = runTest {
         coEvery { outboxDao.getAll() } returns emptyList()
diff --git a/app/src/test/kotlin/org/libremail/data/sync/SyncWorkerTest.kt b/app/src/test/kotlin/org/libremail/data/sync/SyncWorkerTest.kt
index 17faa97..f7126d4 100644
--- a/app/src/test/kotlin/org/libremail/data/sync/SyncWorkerTest.kt
+++ b/app/src/test/kotlin/org/libremail/data/sync/SyncWorkerTest.kt
@@ -15,6 +15,7 @@ import kotlinx.coroutines.test.runTest
 import org.junit.After
 import org.junit.Before
 import org.junit.Test
+import org.libremail.data.local.CacheEncryptionUnavailableException
 import org.libremail.data.security.EncryptedCacheGuard
 import org.libremail.reporting.AppLog
 import org.libremail.reporting.RingLogBuffer
@@ -82,6 +83,24 @@ class SyncWorkerTest {
         assertEquals(ListenableWorker.Result.retry(), worker().doWork())
     }
 
+    // --- issue #359: headless tolerance when SQLCipher's native library is unavailable ------------
+
+    @Test
+    fun `defers with a retry when the encrypted cache is unavailable, without crashing`() = runTest {
+        coEvery { cacheGuard.isCacheLocked() } returns false
+        // The cache is unlocked, so the worker resolves MailSyncer; its first DB access (Room's deferred
+        // cache open) throws because SQLCipher's native library is unavailable on this device (issue #359).
+        // That open is OUTSIDE syncAll's own runCatching, so without the guard it would escape doWork.
+        coEvery { mailSyncer.syncAll() } throws
+            CacheEncryptionUnavailableException(UnsatisfiedLinkError("SQLiteConnection.nativeOpen"))
+
+        assertEquals(ListenableWorker.Result.retry(), worker().doWork())
+
+        val entry = logBuffer.snapshot().single()
+        assertEquals('W', entry.level)
+        assertTrue(entry.message.startsWith("deferred: encrypted cache unavailable"), entry.message)
+    }
+
     // --- issue #329: AppLog breadcrumbs ---------------------------------------------------------
 
     @Test