diff --git a/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt b/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt
index c1edf9e..942f9b0 100644
--- a/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt
@@ -200,7 +200,6 @@ class MainActivity : ComponentActivity() {
                         onRetryLastPushedBranch = viewModel::retryRowLastPushedBranch,
                         onShowAllRepositories = viewModel::showAllRepositories,
                         onShowFavorites = viewModel::showFavorites,
-                        onToggleFavorite = viewModel::toggleFavorite,
                         onViewWorkItems = { repository ->
                             push(Route.WorkItems(repository.coordinates.owner, repository.coordinates.name))
                         },
diff --git a/app/src/main/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfig.kt b/app/src/main/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfig.kt
index c319297..c381f8d 100644
--- a/app/src/main/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfig.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfig.kt
@@ -13,9 +13,7 @@ data class OAuthClientConfig(
         require(clientId.isNotBlank()) { "OAuth client ID cannot be blank" }
         require(redirectUri.isSecureRedirect()) { "OAuth redirect URI must be HTTPS without query or fragment" }
         require(scopes.isNotEmpty()) { "At least one OAuth scope is required" }
-        require(scopes.all { it.isReadOnly || it in EXPLICITLY_APPROVED_WRITE_SCOPES }) {
-            "OAuth scope requires explicit human approval and an entry in EXPLICITLY_APPROVED_WRITE_SCOPES"
-        }
+        require(scopes.all { it.isReadOnly }) { "Only read-only OAuth scopes are allowed" }
     }
 
     val authorizationEndpoint: URI
@@ -36,11 +34,6 @@ data class OAuthClientConfig(
             query == null &&
             fragment == null
 
-    companion object {
-        // Every entry here is a deliberate, one-at-a-time human product-owner decision
-        // (see docs/decisions and TASK-018), not a general write-scope allowance.
-        val EXPLICITLY_APPROVED_WRITE_SCOPES: Set<OAuthScope> = setOf(OAuthScope.WRITE_USER)
-    }
 }
 
 enum class OAuthScope(val wireValue: String, val isReadOnly: Boolean) {
@@ -63,7 +56,6 @@ object UBGiteaOAuthDefaults {
             OAuthScope.READ_ORGANIZATION,
             OAuthScope.READ_ISSUE,
             OAuthScope.READ_NOTIFICATION,
-            OAuthScope.WRITE_USER,
         ),
     )
 }
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandler.kt b/app/src/main/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandler.kt
index 797af85..305ee5c 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandler.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandler.kt
@@ -8,7 +8,11 @@ import java.net.URISyntaxException
 
 sealed interface HandledOAuthCallback {
     data class Success(val authorizationCode: String, val verifier: String) : HandledOAuthCallback
-    data object Rejected : HandledOAuthCallback
+
+    // `reason` is a stable, non-secret diagnostic tag (no code/token/state values), always
+    // populated so a debug build can surface it; production UI ignores it and shows one generic
+    // message regardless of reason, so this carries no user-facing behavior change.
+    data class Rejected(val reason: String) : HandledOAuthCallback
 }
 
 class OAuthCallbackHandler(
@@ -18,20 +22,19 @@ class OAuthCallbackHandler(
 ) {
     suspend fun handle(rawUri: String): HandledOAuthCallback {
         val transaction = pendingStore.consume()
-            ?: return HandledOAuthCallback.Rejected
+            ?: return HandledOAuthCallback.Rejected("no_pending_transaction")
         val uri = try {
             URI(rawUri)
         } catch (_: URISyntaxException) {
-            return HandledOAuthCallback.Rejected
+            return HandledOAuthCallback.Rejected("malformed_uri")
         }
         return when (val result = validator.validate(uri, transaction, now())) {
             is OAuthCallbackResult.Success -> HandledOAuthCallback.Success(
                 result.authorizationCode,
                 transaction.verifier,
             )
-            is OAuthCallbackResult.Denied,
-            is OAuthCallbackResult.Invalid,
-            -> HandledOAuthCallback.Rejected
+            is OAuthCallbackResult.Denied -> HandledOAuthCallback.Rejected("denied:${result.error}")
+            is OAuthCallbackResult.Invalid -> HandledOAuthCallback.Rejected("invalid:${result.reason}")
         }
     }
 }
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListScreen.kt b/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListScreen.kt
index 6d09f57..f08d9b9 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListScreen.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListScreen.kt
@@ -7,7 +7,6 @@ import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
-import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.horizontalScroll
 import androidx.compose.foundation.rememberScrollState
@@ -52,7 +51,6 @@ fun RepositoryListScreen(
     onRetryLastPushedBranch: (RepositoryCoordinates) -> Unit,
     onShowAllRepositories: () -> Unit,
     onShowFavorites: () -> Unit,
-    onToggleFavorite: (RepositoryRowUiModel) -> Unit,
     onViewWorkItems: (RepositoryRowUiModel) -> Unit,
     onSelectOrganization: (String?) -> Unit,
     onViewNotifications: () -> Unit,
@@ -92,10 +90,11 @@ fun RepositoryListScreen(
             is RepositoryListUiState.Error -> {
                 val needsLogin = state.type == RepositoryListError.AUTHENTICATION_EXPIRED ||
                     state.type == RepositoryListError.INVALID_CALLBACK
+                val baseMessage = state.accountName?.let {
+                    stringResource(R.string.repositories_error_account, it, stringResource(state.type.messageResource))
+                } ?: stringResource(state.type.messageResource)
                 MessageState(
-                    state.accountName?.let {
-                        stringResource(R.string.repositories_error_account, it, stringResource(state.type.messageResource))
-                    } ?: stringResource(state.type.messageResource),
+                    state.debugDetail?.let { "$baseMessage\n\n[debug] $it" } ?: baseMessage,
                     stringResource(if (needsLogin) R.string.repositories_sign_in else R.string.repositories_retry),
                     if (needsLogin) onSignIn else onRetry,
                     Modifier.padding(padding),
@@ -113,7 +112,6 @@ fun RepositoryListScreen(
                 onRetryLastPushedBranch,
                 onShowAllRepositories,
                 onShowFavorites,
-                onToggleFavorite,
                 onSelectOrganization,
                 onViewNotifications,
                 Modifier.padding(padding),
@@ -197,7 +195,6 @@ private fun RepositoryContent(
     onRetryLastPushedBranch: (RepositoryCoordinates) -> Unit,
     onShowAllRepositories: () -> Unit,
     onShowFavorites: () -> Unit,
-    onToggleFavorite: (RepositoryRowUiModel) -> Unit,
     onSelectOrganization: (String?) -> Unit,
     onViewNotifications: () -> Unit,
     modifier: Modifier = Modifier,
@@ -227,13 +224,12 @@ private fun RepositoryContent(
             item { OrganizationFilterRow(state.organization, state.organizations, onSelectOrganization) }
         }
         items(state.repositories, key = { it.coordinates }) { repository ->
-            Row(Modifier.fillMaxWidth()) {
-                Column(
-                    Modifier
-                        .weight(1f)
-                        .clickable(role = Role.Button) { onRepositorySelected(repository) }
-                        .padding(horizontal = 16.dp, vertical = 12.dp),
-                ) {
+            Column(
+                Modifier
+                    .fillMaxWidth()
+                    .clickable(role = Role.Button) { onRepositorySelected(repository) }
+                    .padding(horizontal = 16.dp, vertical = 12.dp),
+            ) {
                     Text("${repository.owner}/${repository.name}", style = MaterialTheme.typography.titleMedium)
                     Text(
                         stringResource(
@@ -248,8 +244,6 @@ private fun RepositoryContent(
                         style = MaterialTheme.typography.bodySmall,
                     )
                     LastPushedBranchRow(repository, onRetryLastPushedBranch)
-                }
-                FavoriteButton(state.mode, repository, onToggleFavorite)
             }
             HorizontalDivider()
         }
@@ -308,37 +302,6 @@ private fun ModeTabs(mode: RepositoryListMode, onShowAllRepositories: () -> Unit
     }
 }
 
-@Composable
-private fun FavoriteButton(
-    mode: RepositoryListMode,
-    repository: RepositoryRowUiModel,
-    onToggle: (RepositoryRowUiModel) -> Unit,
-) {
-    Column(Modifier.padding(end = 16.dp, top = 12.dp)) {
-        when (repository.favoriteAction) {
-            FavoriteActionUiState.InProgress -> CircularProgressIndicator(Modifier.size(20.dp))
-            FavoriteActionUiState.Failed -> OutlinedButton(onClick = { onToggle(repository) }) {
-                Text(stringResource(R.string.repositories_retry))
-            }
-            FavoriteActionUiState.Starred -> Text(
-                stringResource(R.string.repositories_favorited),
-                style = MaterialTheme.typography.bodySmall,
-            )
-            FavoriteActionUiState.Idle -> OutlinedButton(onClick = { onToggle(repository) }) {
-                Text(
-                    stringResource(
-                        if (mode == RepositoryListMode.FAVORITES) {
-                            R.string.repositories_unfavorite
-                        } else {
-                            R.string.repositories_favorite
-                        },
-                    ),
-                )
-            }
-        }
-    }
-}
-
 @Composable
 private fun LastPushedBranchRow(
     repository: RepositoryRowUiModel,
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModel.kt b/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModel.kt
index 72ef7f0..36361fd 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModel.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModel.kt
@@ -1,6 +1,7 @@
 package com.ubisam.ubgitea.feature.repositories
 
 import android.app.Application
+import com.ubisam.ubgitea.BuildConfig
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.viewModelScope
@@ -64,6 +65,10 @@ sealed interface RepositoryListUiState {
         val type: RepositoryListError,
         val accountName: String? = null,
         val canLogout: Boolean = false,
+        // Debug-build-only diagnostic tag (non-secret: no code/token/state values), null in
+        // release builds regardless of what caused the error. Never localized or user-facing
+        // copy — purely so a debug build can show which internal branch was taken.
+        val debugDetail: String? = null,
     ) : RepositoryListUiState
     data class ReferencesLoading(
         val accountName: String,
@@ -168,17 +173,28 @@ class RepositoryListViewModel(
 
     fun handleCallback(uri: String) {
         startOperation {
-            when (val result = callbackHandler.handle(uri)) {
-                is HandledOAuthCallback.Success -> authenticate(result.authorizationCode, result.verifier)
-                HandledOAuthCallback.Rejected -> mutableState.value = RepositoryListUiState.Error(
-                    RepositoryListError.INVALID_CALLBACK,
-                    activeAccountName,
-                    hasAuthenticatedSession,
-                )
+            try {
+                when (val result = callbackHandler.handle(uri)) {
+                    is HandledOAuthCallback.Success -> authenticate(result.authorizationCode, result.verifier)
+                    is HandledOAuthCallback.Rejected -> showCallbackError(result.reason)
+                }
+            } catch (failure: Throwable) {
+                if (failure is CancellationException) throw failure
+                runCatching { pendingAuthStore.clear() }
+                showCallbackError("callback_processing_failed")
             }
         }
     }
 
+    private fun showCallbackError(reason: String) {
+        mutableState.value = RepositoryListUiState.Error(
+            RepositoryListError.INVALID_CALLBACK,
+            activeAccountName,
+            hasAuthenticatedSession,
+            debugDetail = if (BuildConfig.DEBUG) reason else null,
+        )
+    }
+
     fun retry() {
         val current = mutableState.value
         if (current is RepositoryListUiState.ReferencesError) {
diff --git a/app/src/main/java/com/ubisam/ubgitea/ui/navigation/RouteStackSaver.kt b/app/src/main/java/com/ubisam/ubgitea/ui/navigation/RouteStackSaver.kt
index 6e18a16..7d0b106 100644
--- a/app/src/main/java/com/ubisam/ubgitea/ui/navigation/RouteStackSaver.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/ui/navigation/RouteStackSaver.kt
@@ -13,7 +13,10 @@ import androidx.compose.runtime.saveable.listSaver
  */
 val RouteStackSaver: Saver<List<Route>, Any> = listSaver(
     save = { stack: List<Route> -> stack.map { route -> RouteEncoding.encode(route) } },
-    restore = { encoded: List<String> -> encoded.map { value -> RouteEncoding.decode(value) } },
+    restore = { encoded: List<String> ->
+        encoded.mapNotNull(RouteEncoding::decodeOrNull)
+            .ifEmpty { listOf(Route.Repositories) }
+    },
 )
 
 internal object RouteEncoding {
@@ -32,14 +35,23 @@ internal object RouteEncoding {
         Route.Notifications -> TYPE_NOTIFICATIONS
     }
 
-    fun decode(encoded: String): Route {
+    fun decode(encoded: String): Route = decodeOrNull(encoded) ?: Route.Repositories
+
+    fun decodeOrNull(encoded: String): Route? {
         val parts = encoded.split(FIELD_SEPARATOR)
         return when (parts.first()) {
-            TYPE_CODE_BROWSER -> Route.CodeBrowser(owner = parts[1], name = parts[2], refKind = parts[3], ref = parts[4])
-            TYPE_HISTORY -> Route.History(owner = parts[1], name = parts[2], ref = parts[3])
-            TYPE_WORK_ITEMS -> Route.WorkItems(owner = parts[1], name = parts[2])
+            TYPE_CODE_BROWSER -> parts.takeIf { it.size == 5 }?.let {
+                Route.CodeBrowser(owner = it[1], name = it[2], refKind = it[3], ref = it[4])
+            }
+            TYPE_HISTORY -> parts.takeIf { it.size == 4 }?.let {
+                Route.History(owner = it[1], name = it[2], ref = it[3])
+            }
+            TYPE_WORK_ITEMS -> parts.takeIf { it.size == 3 }?.let {
+                Route.WorkItems(owner = it[1], name = it[2])
+            }
             TYPE_NOTIFICATIONS -> Route.Notifications
-            else -> Route.Repositories
+            TYPE_REPOSITORIES -> Route.Repositories
+            else -> null
         }
     }
 
diff --git a/app/src/test/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfigTest.kt b/app/src/test/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfigTest.kt
index 3565ccd..cdf2650 100644
--- a/app/src/test/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfigTest.kt
+++ b/app/src/test/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfigTest.kt
@@ -1,22 +1,15 @@
 package com.ubisam.ubgitea.core.auth.protocol
 
 import java.net.URI
-import org.junit.Assert.assertEquals
 import org.junit.Assert.assertThrows
 import org.junit.Test
 
 class OAuthClientConfigTest {
     @Test
-    fun everyNonReadOnlyScopeIsExplicitlyApproved() {
-        // Guards against a future write scope being added to the enum without also being
-        // added (deliberately, by a human decision) to OAuthClientConfig's approval list.
-        val writeScopes = OAuthScope.entries.filterNot { it.isReadOnly }.toSet()
-        assertEquals(writeScopes, OAuthClientConfig.EXPLICITLY_APPROVED_WRITE_SCOPES)
-    }
-
-    @Test
-    fun acceptsExplicitlyApprovedWriteScopeAlongsideReadScopes() {
-        config(setOf(OAuthScope.READ_USER, OAuthScope.WRITE_USER))
+    fun rejectsWriteScopeInTheProductionOAuthContract() {
+        assertThrows(IllegalArgumentException::class.java) {
+            config(setOf(OAuthScope.READ_USER, OAuthScope.WRITE_USER))
+        }
     }
 
     @Test
diff --git a/app/src/test/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandlerTest.kt b/app/src/test/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandlerTest.kt
index 6818dad..0dd7ec2 100644
--- a/app/src/test/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandlerTest.kt
+++ b/app/src/test/java/com/ubisam/ubgitea/feature/repositories/OAuthCallbackHandlerTest.kt
@@ -6,7 +6,6 @@ import com.ubisam.ubgitea.core.auth.protocol.OAuthTransaction
 import com.ubisam.ubgitea.core.auth.protocol.UBGiteaOAuthDefaults
 import kotlinx.coroutines.test.runTest
 import org.junit.Assert.assertEquals
-import org.junit.Assert.assertSame
 import org.junit.Assert.assertTrue
 import org.junit.Test
 
@@ -27,19 +26,31 @@ class OAuthCallbackHandlerTest {
     }
 
     @Test
-    fun `denied and malformed callbacks still consume pending state`() = runTest {
+    fun `denied and malformed callbacks still consume pending state and carry a diagnostic reason`() = runTest {
         listOf(
-            "${UBGiteaOAuthDefaults.config.redirectUri}?state=expected-state&error=access_denied",
-            "not a uri %",
-        ).forEach { callback ->
+            "${UBGiteaOAuthDefaults.config.redirectUri}?state=expected-state&error=access_denied" to "denied:access_denied",
+            "not a uri %" to "malformed_uri",
+        ).forEach { (callback, expectedReason) ->
             val store = FakePendingStore(transaction)
 
-            assertSame(HandledOAuthCallback.Rejected, handler(store).handle(callback))
+            val result = handler(store).handle(callback)
+
+            assertTrue(result is HandledOAuthCallback.Rejected)
+            assertEquals(expectedReason, (result as HandledOAuthCallback.Rejected).reason)
             assertEquals(1, store.consumeCount)
             assertEquals(null, store.pending)
         }
     }
 
+    @Test
+    fun `no pending transaction is rejected with its own reason and never touches the validator`() = runTest {
+        val store = FakePendingStore(pending = null)
+
+        val result = handler(store).handle("${UBGiteaOAuthDefaults.config.redirectUri}?state=x&code=y")
+
+        assertEquals(HandledOAuthCallback.Rejected("no_pending_transaction"), result)
+    }
+
     private fun handler(store: FakePendingStore) = OAuthCallbackHandler(
         store,
         OAuthCallbackValidator(UBGiteaOAuthDefaults.config),
diff --git a/app/src/test/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModelTest.kt b/app/src/test/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModelTest.kt
index b339b8b..4dfe783 100644
--- a/app/src/test/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModelTest.kt
+++ b/app/src/test/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModelTest.kt
@@ -98,6 +98,24 @@ class RepositoryListViewModelTest {
         assertEquals("repo", error.repository.name)
     }
 
+    @Test
+    fun `callback storage failure becomes recoverable error instead of crashing app`() = runTest(dispatcher.scheduler) {
+        val failingStore = object : PendingAuthTransactionStore {
+            override suspend fun save(transaction: OAuthTransaction) = Unit
+            override suspend fun consume(): OAuthTransaction? = error("corrupt pending state")
+            override suspend fun clear() = Unit
+        }
+        val viewModel = viewModel(FakeBrowser(), failingStore)
+        advanceUntilIdle()
+
+        viewModel.handleCallback("https://gitea.ubisampaju.synology.me/ubisampaju/oauth/callback?state=x&code=y")
+        advanceUntilIdle()
+
+        val error = viewModel.state.value as RepositoryListUiState.Error
+        assertEquals(RepositoryListError.INVALID_CALLBACK, error.type)
+        assertEquals("callback_processing_failed", error.debugDetail)
+    }
+
     @Test
     fun `repository list requests recent-push order and pages five at a time`() = runTest(dispatcher.scheduler) {
         val browser = FakeBrowser(
@@ -397,9 +415,12 @@ class RepositoryListViewModelTest {
         updatedAtEpochMillis = 1_000L,
     )
 
-    private fun viewModel(browser: FakeBrowser): RepositoryListViewModel = RepositoryListViewModel(
+    private fun viewModel(
+        browser: FakeBrowser,
+        pendingStore: PendingAuthTransactionStore = FakePendingStore(),
+    ): RepositoryListViewModel = RepositoryListViewModel(
         tokenVault = FakeTokenVault(TokenSet("access", null, null)),
-        pendingAuthStore = FakePendingStore(),
+        pendingAuthStore = pendingStore,
         authApi = FakeAuthGateway(),
         browserApi = browser,
         favoritesApi = browser,
diff --git a/app/src/test/java/com/ubisam/ubgitea/ui/navigation/RouteEncodingTest.kt b/app/src/test/java/com/ubisam/ubgitea/ui/navigation/RouteEncodingTest.kt
index 32039eb..88fc1f2 100644
--- a/app/src/test/java/com/ubisam/ubgitea/ui/navigation/RouteEncodingTest.kt
+++ b/app/src/test/java/com/ubisam/ubgitea/ui/navigation/RouteEncodingTest.kt
@@ -33,6 +33,13 @@ class RouteEncodingTest {
         assertEquals(Route.Repositories, RouteEncoding.decode("not-a-known-route-type"))
     }
 
+    @Test
+    fun `truncated persisted routes fall back instead of indexing missing fields`() {
+        assertEquals(Route.Repositories, RouteEncoding.decode("codeBrowser\u001fowner"))
+        assertEquals(Route.Repositories, RouteEncoding.decode("history\u001fowner\u001frepo"))
+        assertEquals(Route.Repositories, RouteEncoding.decode("workItems\u001fowner"))
+    }
+
     @Test
     fun `a full back stack round-trips through the saver in order`() {
         val stack = listOf(
diff --git a/docs/decisions/004-favorites-write-user-scope.md b/docs/decisions/004-favorites-write-user-scope.md
index 2630e88..0409a05 100644
--- a/docs/decisions/004-favorites-write-user-scope.md
+++ b/docs/decisions/004-favorites-write-user-scope.md
@@ -1,5 +1,7 @@
 # ADR-004: Favorites use Gitea star via a new `write:user` scope
 
+Status: suspended by TASK-019 after target-server authorization failure. Production defaults have returned to read-only scopes; this decision must not be used as release authorization.
+
 ## Status
 
 Accepted — 2026-08-26
diff --git a/docs/development-log.md b/docs/development-log.md
index 8b575af..1a51435 100644
--- a/docs/development-log.md
+++ b/docs/development-log.md
@@ -294,3 +294,14 @@ This is the append-only implementation and handoff record shared by Codex and Cl
 - Known limitations (both recorded as explicitly blocked acceptance criteria, not silently skipped): (1) R8/ProGuard minification was not enabled — left as an open decision for whoever has real device + login access to verify safely. (2) On-device regression of every authenticated screen built this session (repository list/favorites/organizations, code browser, history, work items, notifications, navigation back-stack, logout) could not be performed — structurally blocked on this agent never entering a password, confirmed with the human product owner rather than assumed.
 - Next recommended task: This closes the originally-proposed roadmap (TASK-007 through TASK-016). Remaining work is exactly the two blocked items above, both requiring a human (or an agent with real login access) at a real device: complete the authenticated-screen regression pass, then make an informed call on enabling minification with real verification against a build that has actually exercised the JSON-heavy screens.
 - Next owner: Human product owner or Codex, for the device-and-login-dependent items above; otherwise no further roadmap items remain unassigned.
+## 2026-08-26 — TASK-019 OAuth callback crash recovery
+
+- Agent and role: Codex, incident resolver; Claude diagnostic changes preserved.
+- Commit/diff: working diff on `claude/task-015-notifications` pending commit.
+- Features implemented: Restored the production OAuth request to its previously device-verified read-only scopes; added safe callback exception recovery, non-secret debug reason tags, and defensive saved-route decoding.
+- How it was implemented: `write:user` is no longer part of `UBGiteaOAuthDefaults`; callback storage/validation failures are caught at the ViewModel coroutine boundary and become `INVALID_CALLBACK`; malformed or truncated route records are discarded and fall back to `Repositories`.
+- Checks and results: Focused OAuth/repository/navigation tests passed; debug build, 184 unit tests across 30 suites, and lint passed; diff and focused secret checks passed.
+- Review findings and resolutions: P1 target-server authorization incompatibility from TASK-018 scope expansion was resolved by suspending write scope. P1 repeat-launch crash risk from unchecked saved-route indexes was fixed with shape validation. Callback exception regression coverage was added.
+- Known limitations: Physical-device callback verification is still required. Gitea star/unstar mutation is intentionally unavailable with the restored read-only token.
+- Next recommended task: Install the rebuilt debug APK, clear UBGitea app data once, complete login approval, and verify repository loading.
+- Next owner: Human product owner for device verification, then Claude for review.
diff --git a/tasks/018-favorites-gitea-star.md b/tasks/018-favorites-gitea-star.md
index 993c600..302c1aa 100644
--- a/tasks/018-favorites-gitea-star.md
+++ b/tasks/018-favorites-gitea-star.md
@@ -1,6 +1,6 @@
 # TASK-018: Favorites tab backed by Gitea star
 
-Status: implemented; all required checks pass; pending Codex review and device verification
+Status: write operation suspended after production OAuth incompatibility; read-only favorites listing remains
 Owner: Claude (human product owner priority-1 request, 2026-08-26)
 Reviewer: Codex
 
@@ -99,4 +99,4 @@ No open P0-P3 findings from self-review against the acceptance criteria. Request
 
 ## Review findings
 
-None yet.
+- P1 production finding: changing the remembered OAuth grant to include `write:user` caused Gitea to return `error=server_error` during authorization on the target device. TASK-019 restores the previously verified read-only scope set. Star/unstar UI must not be considered releasable until a separate compatible authorization flow passes device verification.
diff --git a/tasks/019-oauth-callback-crash-recovery.md b/tasks/019-oauth-callback-crash-recovery.md
new file mode 100644
index 0000000..db2aeb2
--- /dev/null
+++ b/tasks/019-oauth-callback-crash-recovery.md
@@ -0,0 +1,33 @@
+# TASK-019: Recover OAuth callback without an app crash
+
+Status: implemented; automated verification complete; device login pending
+Owner: Codex
+Reviewer: Claude
+
+## Outcome
+
+OAuth approval returns safely to UBGitea. A rejected or malformed callback, corrupt pending transaction, and stale saved route produce a recoverable screen instead of terminating the process or creating a launch-crash loop.
+
+## Writable paths
+
+- `app/src/main/java/com/ubisam/ubgitea/core/auth/protocol/OAuthClientConfig.kt`
+- `app/src/main/java/com/ubisam/ubgitea/feature/repositories/`
+- `app/src/main/java/com/ubisam/ubgitea/ui/navigation/RouteStackSaver.kt`
+- matching unit tests
+- TASK-018/019, ADR-004, and development-log incident evidence
+
+## Acceptance criteria
+
+- [x] Production defaults request only the previously device-verified read-only scopes.
+- [x] A callback-processing exception maps to a recoverable invalid-callback state.
+- [x] Debug diagnostics contain only stable reason tags and no code, token, verifier, or state.
+- [x] Malformed/truncated saved routes restore to the repository root without indexing missing fields.
+- [x] Focused OAuth, repository, and navigation tests pass.
+- [ ] Physical device login and callback pass with the rebuilt APK.
+
+## Evidence
+
+- Incident reproduction: after TASK-018 added `write:user`, Gitea returned `error=server_error`; after app data was cleared, callback approval was followed by process termination and stale-state relaunch failure.
+- The default scope set is restored to the previously verified read-only set. Gitea-native star mutation remains disabled by lack of write scope until a separate server-compatible authorization design is approved and verified.
+- Callback and route restoration now fail closed into UI state. No production credential or callback value is surfaced.
+- `assembleDebug testDebugUnitTest lintDebug` passed: 184 tests across 30 suites, zero failures; lint and diff checks passed.