Second on-device feedback round: eight fixes, and a measured retry policy

The ghost bookcase was an inset bug, not a data bug. LocationsScreen's list
branch dropped the Scaffold's innerPadding while its empty-state branch applied
it, so the first bookcase row rendered under the top app bar and was invisible.
Both of the user's bookcases were always real; they just could not see the first
one, so they made a second. Every other screen was checked for the same class of
bug — Locations was the only one.

Metadata lookup is now designed against a measurement rather than a guess
(docs/METADATA-SOURCES.md § "Measured again 2026-09-09"):

  - Google Books keyless is dead for everyone, permanently. The user's
    residential-IP test returned a quota error naming a shared anonymous PROJECT,
    not an IP, so the earlier "your phone may well get answers" guess is wrong and
    is now marked CORRECTED in place. Because combine() turns any Failed-with-no-
    Found into Unavailable, that standing failure meant every Open Library hiccup
    surfaced as "one or more sources couldn't be reached". The API key is
    deliberately deferred by the user; this commit leaves the source broken.

  - Our own timeouts were manufacturing failures. Over 30 live requests, 13%
    failed — all fast TLS resets under 2.5s — while successes ran to a median of
    4.3s and a max of 22.0s. Two of 26 successes exceeded the old 12s callTimeout,
    so ~8% of lookups that were about to work were cancelled and reported as
    unreachable. Timeouts are now 25s/20s/20s.

That asymmetry (cheap failures, expensive successes) is what RetryPolicy encodes.
It retries TRANSPORT and SERVER_ERROR with a 250ms/750ms jittered backoff, and
deliberately does not retry TIMEOUT (the budget is already spent) or RATE_LIMITED
(hammering a quota is how an intermittent block becomes a permanent one — this
project's IP has already been refused outright once during research).

SourceResult.Failed now carries a FailureKind alongside its human reason, and the
reason names the specific failure ("tls connection reset, 3 attempts") instead of
a generic "network error". That string was already threaded to the UI and dropped
on the floor; LookupFailedSheet now renders it. It is the only diagnostic channel
we have from a real phone, so nothing may parse it.

Also from the same feedback round:
  - Grouped ModalBottomSheet shelf picker, replacing two near-duplicate flat
    dropdowns that listed every bookcase x shelf pair. Sections per bookcase,
    empty bookcases say so, and the most recently used shelf is pinned on top.
  - The recent shelf persists across sessions (SettingsStore.LAST_SHELF_ID) and is
    cleared on sign-out. It is offered, never pre-selected: the user weighed that
    and chose one tap over the risk of silently mis-shelving a book.
  - Locations dialogs and the manual-ISBN dialog auto-focus their first field.
  - The library filter menu offers "Add a bookcase to enable filtering" instead of
    a lone "All books" that is already the active state and cannot be changed.
  - The Locations button is Material Symbols' "shelves" (a bookcase) instead of
    Warehouse (a barn). material-icons-extended 1.7.8 has no bookcase glyph.
  - The scan sheet drops "you can lower the book" — the ISBN echo already says it.

assembleDebug exit 0; testDebugUnitTest 172 tests, 1 skipped, 0 failures (was
138); verifyPaparazziDebug exit 0; assembleRelease exit 0, signed with the real
release key; zero "always 'false'" warnings on a --rerun-tasks rebuild.

Three soft spots are recorded in docs/HANDOFF.md and are NOT verified: the
ghost-bookcase Paparazzi snapshot renders a lookalike of the screen rather than
the screen, the auto-focus calls swallow their own failure and no emulator exists
here, and the picker opens as a sheet stacked on the save sheet.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LSnVqWdiQNEcPFRq1hGZAi

app/app/src/main/java/org/modg/bookshelf/AppContainer.kt

@@ -93,11 +93,24 @@ class AppContainer(private val context: Context) {
     // server. A call timeout is load-bearing here: with none, a stalled
     // connection hangs on OkHttp's default (unbounded) socket timeouts, and the
     // user is standing at a bookshelf waiting on it.
+    //
+    // These were 12s/10s/10s and were MANUFACTURING failures. Measuring the exact
+    // Open Library call 30 times on 2026-09-09 (docs/METADATA-SOURCES.md) found
+    // successful requests with a median of 4.3s but a long tail — p90 9.2s, max
+    // 22.0s, and one connect phase alone of 19.6s. Two of 26 successes exceeded the
+    // old 12s call timeout, so ~8% of lookups that were about to work were being
+    // cancelled and reported to the user as "couldn't be reached".
+    //
+    // Raising these does NOT slow the failure path: every observed failure was a
+    // TLS-stage reset returning in under 2.5s, and a socket that is going to break
+    // breaks long before any of these limits. The timeouts only ever bound the
+    // slow-success tail, which is precisely what we want to stop truncating.
+    // 25s > the 22.0s worst observed success, with room to spare.
     private val metadataHttpClient: OkHttpClient by lazy {
         OkHttpClient.Builder()
-            .callTimeout(12, TimeUnit.SECONDS)
+            .callTimeout(25, TimeUnit.SECONDS)
-            .connectTimeout(10, TimeUnit.SECONDS)
+            .connectTimeout(20, TimeUnit.SECONDS)
-            .readTimeout(10, TimeUnit.SECONDS)
+            .readTimeout(20, TimeUnit.SECONDS)
             .build()
     }
 

app/app/src/main/java/org/modg/bookshelf/data/metadata/GoogleBooksClient.kt

@@ -1,7 +1,6 @@
 package org.modg.bookshelf.data.metadata
 
 import java.io.IOException
-import java.net.SocketTimeoutException
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
 import kotlinx.serialization.SerializationException
@@ -20,7 +19,18 @@ class GoogleBooksClient(
 ) {
     private val json = Json(from = json) { ignoreUnknownKeys = true }
 
-    suspend fun lookup(isbn13: String): SourceResult = withContext(Dispatchers.IO) { fetch(isbn13) }
+    /**
+     * Retries transient failures per [RetryPolicy]. Note this source's standing
+     * failure — keyless requests share one exhausted global quota and answer 429,
+     * which [RetryPolicy] deliberately does NOT retry, so today this costs nothing
+     * and changes nothing here. See docs/METADATA-SOURCES.md.
+     */
+    suspend fun lookup(isbn13: String): SourceResult =
+        withContext(Dispatchers.IO) { withRetry { fetch(isbn13) } }
+
+    /** Single un-retried attempt, for tests that need to count calls. */
+    internal suspend fun lookupOnce(isbn13: String): SourceResult =
+        withContext(Dispatchers.IO) { fetch(isbn13) }
 
     private fun fetch(isbn13: String): SourceResult = try {
         val request = Request.Builder()
@@ -29,10 +39,8 @@ class GoogleBooksClient(
         httpClient.newCall(request).execute().use { response ->
             classify(response.code, response.body.string())
         }
-    } catch (e: SocketTimeoutException) {
-        SourceResult.Failed("timeout")
     } catch (e: IOException) {
-        SourceResult.Failed("network error")
+        SourceResult.fromException(e)
     }
 
     /**
@@ -42,16 +50,16 @@ class GoogleBooksClient(
      * can never disagree about what a body means.
      */
     internal fun classify(httpCode: Int, body: String?): SourceResult {
-        if (httpCode !in 200..299) return SourceResult.Failed("http $httpCode")
+        if (httpCode !in 200..299) return SourceResult.fromHttpCode(httpCode)
-        if (body.isNullOrBlank()) return SourceResult.Failed("empty body")
+        if (body.isNullOrBlank()) return SourceResult.Failed("empty body", FailureKind.MALFORMED)
         return try {
             val dto = json.decodeFromString(GoogleBooksResponseDto.serializer(), body)
             val metadata = dto.items.firstOrNull()?.volumeInfo?.toBookMetadata()
             if (metadata != null) SourceResult.Found(metadata) else SourceResult.NotFound
         } catch (e: SerializationException) {
-            SourceResult.Failed("malformed json")
+            SourceResult.Failed("malformed json", FailureKind.MALFORMED)
         } catch (e: IllegalArgumentException) {
-            SourceResult.Failed("malformed json")
+            SourceResult.Failed("malformed json", FailureKind.MALFORMED)
         }
     }
 

app/app/src/main/java/org/modg/bookshelf/data/metadata/OpenLibraryClient.kt

@@ -1,7 +1,6 @@
 package org.modg.bookshelf.data.metadata
 
 import java.io.IOException
-import java.net.SocketTimeoutException
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
 import kotlinx.serialization.SerializationException
@@ -23,7 +22,17 @@ class OpenLibraryClient(
     // Real responses carry fields this DTO doesn't model; never let an unknown key throw.
     private val json = Json(from = json) { ignoreUnknownKeys = true }
 
-    suspend fun lookup(isbn13: String): SourceResult = withContext(Dispatchers.IO) { fetch(isbn13) }
+    /**
+     * Retries transient failures per [RetryPolicy]. Measured against the live API,
+     * 13% of requests fail at the TLS stage in well under a second while successful
+     * ones take seconds — so a retry is nearly free and removes most of that 13%.
+     */
+    suspend fun lookup(isbn13: String): SourceResult =
+        withContext(Dispatchers.IO) { withRetry { fetch(isbn13) } }
+
+    /** Single un-retried attempt, for tests that need to count calls. */
+    internal suspend fun lookupOnce(isbn13: String): SourceResult =
+        withContext(Dispatchers.IO) { fetch(isbn13) }
 
     private fun fetch(isbn13: String): SourceResult = try {
         val request = Request.Builder()
@@ -32,10 +41,8 @@ class OpenLibraryClient(
         httpClient.newCall(request).execute().use { response ->
             classify(response.code, response.body.string(), isbn13)
         }
-    } catch (e: SocketTimeoutException) {
-        SourceResult.Failed("timeout")
     } catch (e: IOException) {
-        SourceResult.Failed("network error")
+        SourceResult.fromException(e)
     }
 
     /**
@@ -45,16 +52,16 @@ class OpenLibraryClient(
      * can never disagree about what a body means.
      */
     internal fun classify(httpCode: Int, body: String?, isbn13: String): SourceResult {
-        if (httpCode !in 200..299) return SourceResult.Failed("http $httpCode")
+        if (httpCode !in 200..299) return SourceResult.fromHttpCode(httpCode)
-        if (body.isNullOrBlank()) return SourceResult.Failed("empty body")
+        if (body.isNullOrBlank()) return SourceResult.Failed("empty body", FailureKind.MALFORMED)
         return try {
             val root = json.parseToJsonElement(body).jsonObject
             val entry = root["ISBN:$isbn13"]?.jsonObject ?: return SourceResult.NotFound
             SourceResult.Found(json.decodeFromJsonElement<OpenLibraryBookDto>(entry).toBookMetadata(isbn13))
         } catch (e: SerializationException) {
-            SourceResult.Failed("malformed json")
+            SourceResult.Failed("malformed json", FailureKind.MALFORMED)
         } catch (e: IllegalArgumentException) {
-            SourceResult.Failed("malformed json")
+            SourceResult.Failed("malformed json", FailureKind.MALFORMED)
         }
     }
 

app/app/src/main/java/org/modg/bookshelf/data/metadata/RetryPolicy.kt

@@ -0,0 +1,110 @@
+package org.modg.bookshelf.data.metadata
+
+import kotlin.random.Random
+import kotlinx.coroutines.delay
+
+/**
+ * When a failed lookup attempt is worth repeating, and how long to wait first.
+ *
+ * Grounded in a measurement of the live Open Library API from 2026-09-09 — 30
+ * requests, the exact call [OpenLibraryClient] makes (see docs/METADATA-SOURCES.md):
+ *
+ *   - 13% of requests failed, every one of them a TLS-stage connection reset.
+ *   - Failures were FAST: 0.23s, 0.31s, 0.59s, 2.46s.
+ *   - Successes were SLOW and long-tailed: median 4.3s, p90 9.2s, max 22.0s.
+ *
+ * That asymmetry drives every constant here. A retry costs roughly a fifth of a
+ * second of the user's time and turns a 13% failure rate into ~1.7% at two
+ * attempts and ~0.2% at three, which is why the backoff is short rather than the
+ * conventional exponential-with-seconds. It is also why [isRetryable] refuses to
+ * repeat a [FailureKind.TIMEOUT]: a timeout means we already spent the full budget
+ * on that attempt, so repeating it risks tripling the wait for a user standing at
+ * a bookshelf, and the measurement says slow requests usually eventually succeed
+ * rather than fail — the fix for those is a generous timeout, not another attempt.
+ */
+object RetryPolicy {
+
+    /** One original attempt plus two retries. Beyond this the marginal gain is noise. */
+    const val MAX_ATTEMPTS = 3
+
+    /**
+     * Stop starting NEW attempts once this much time has gone into a single source.
+     * A backstop against pathological cases (every attempt hitting the slow tail),
+     * not a normal-path limit. It is deliberately checked only BETWEEN attempts —
+     * an in-flight request is never cancelled, because the 22-second request in the
+     * sample was a successful one and killing it would manufacture exactly the
+     * failure this whole change exists to remove.
+     */
+    const val TOTAL_BUDGET_MILLIS = 30_000L
+
+    /**
+     * [FailureKind.TRANSPORT] and [FailureKind.SERVER_ERROR] are transient and
+     * cheap to re-ask. The rest are not:
+     *  - TIMEOUT      — the budget is already spent; see the class KDoc.
+     *  - RATE_LIMITED — the source is explicitly asking us to stop. Hammering a
+     *                   quota is how an intermittent block becomes a permanent one,
+     *                   and METADATA-SOURCES.md records that happening to this
+     *                   project's IP during research. When the Google Books API key
+     *                   lands, revisit this: a keyed 429 is a per-second rate limit
+     *                   and IS worth one Retry-After-respecting retry, unlike
+     *                   today's keyless daily-quota 429, which never clears.
+     *  - CLIENT_ERROR — an identical request gets an identical answer.
+     *  - MALFORMED    — same bytes, same parse failure.
+     */
+    fun isRetryable(kind: FailureKind): Boolean =
+        kind == FailureKind.TRANSPORT || kind == FailureKind.SERVER_ERROR
+
+    /**
+     * Backoff before attempt number [nextAttempt] (2-based: the wait before the
+     * first retry is `backoffMillis(2)`). 250ms then 750ms, plus up to 40% jitter
+     * so that two sources — or two phones in the same house — cannot fall into
+     * lockstep and hammer a recovering server in unison.
+     */
+    fun backoffMillis(nextAttempt: Int, random: Random = Random.Default): Long {
+        val base = when (nextAttempt) {
+            2 -> 250L
+            else -> 750L
+        }
+        return base + random.nextLong(0, (base * 0.4).toLong().coerceAtLeast(1))
+    }
+}
+
+/**
+ * Runs [attempt] until it succeeds, fails un-retryably, or runs out of attempts or
+ * budget. Returns the LAST result, so the caller always sees a real outcome rather
+ * than a synthesised one.
+ *
+ * A [SourceResult.Failed] that survives retrying has its attempt count appended to
+ * [SourceResult.Failed.reason] ("tls connection reset, 3 attempts"). That string is
+ * shown to the user on the scan sheet and is the only diagnostic we get back from a
+ * real phone — "failed once" and "failed three times in a row" are very different
+ * stories about the network, and without this they are indistinguishable.
+ *
+ * [sleep] and [nowMillis] are injectable purely so tests can run the real policy
+ * with no wall-clock delay; production callers use the defaults.
+ */
+suspend fun withRetry(
+    maxAttempts: Int = RetryPolicy.MAX_ATTEMPTS,
+    budgetMillis: Long = RetryPolicy.TOTAL_BUDGET_MILLIS,
+    random: Random = Random.Default,
+    nowMillis: () -> Long = { System.currentTimeMillis() },
+    sleep: suspend (Long) -> Unit = { delay(it) },
+    attempt: suspend () -> SourceResult,
+): SourceResult {
+    val started = nowMillis()
+    var last: SourceResult = attempt()
+    var attemptsMade = 1
+
+    while (attemptsMade < maxAttempts) {
+        val failure = last as? SourceResult.Failed ?: return last
+        if (!RetryPolicy.isRetryable(failure.kind)) break
+        if (nowMillis() - started >= budgetMillis) break
+
+        sleep(RetryPolicy.backoffMillis(attemptsMade + 1, random))
+        last = attempt()
+        attemptsMade++
+    }
+
+    val failure = last as? SourceResult.Failed ?: return last
+    return if (attemptsMade > 1) failure.copy(reason = "${failure.reason}, $attemptsMade attempts") else failure
+}

app/app/src/main/java/org/modg/bookshelf/data/metadata/SourceResult.kt

@@ -1,5 +1,39 @@
 package org.modg.bookshelf.data.metadata
 
+import java.io.IOException
+import java.io.InterruptedIOException
+import java.net.ConnectException
+import java.net.SocketException
+import java.net.SocketTimeoutException
+import java.net.UnknownHostException
+import javax.net.ssl.SSLException
+import javax.net.ssl.SSLHandshakeException
+
+/**
+ * Why a source failed, in the only terms that matter to a caller: is it worth
+ * asking again? [RetryPolicy] is the single place that decides, so the answer
+ * cannot drift between the two clients.
+ */
+enum class FailureKind {
+    /** Never got an answer: DNS, refused connection, reset socket, failed TLS handshake. */
+    TRANSPORT,
+
+    /** We gave up waiting. Distinct from [TRANSPORT] because the budget is already spent. */
+    TIMEOUT,
+
+    /** HTTP 429. The source is telling us to stop asking; asking harder is the wrong move. */
+    RATE_LIMITED,
+
+    /** HTTP 5xx — the source's problem, and usually a passing one. */
+    SERVER_ERROR,
+
+    /** HTTP 4xx other than 429. Repeating an identical request cannot change the answer. */
+    CLIENT_ERROR,
+
+    /** 2xx whose body we could not parse. Deterministic: the same bytes will fail again. */
+    MALFORMED,
+}
+
 /**
  * Per-source lookup outcome (SPEC.md "Book metadata lookup": "Lookup outcome is
  * THREE-WAY, never a bare null"). [OpenLibraryClient] and [GoogleBooksClient] each
@@ -14,10 +48,54 @@ sealed interface SourceResult {
     data object NotFound : SourceResult
 
     /**
-     * The source could not be asked, or its answer couldn't be trusted: non-2xx,
+     * The source could not be asked, or its answer couldn't be trusted. [reason] is
-     * timeout, transport error, or a body that didn't parse. [reason] is a short
+     * a short diagnostic ("http 429", "tls reset", "malformed json") that is shown
-     * diagnostic ("http 429", "timeout", "malformed json") for logs — never shown
+     * to the user as supplementary detail on the scan sheet and is our ONLY
-     * to the user verbatim.
+     * diagnostic channel from a real phone — so it names the specific failure, not
+     * a generic one. [kind] is the same fact in a form [RetryPolicy] can act on;
+     * nothing should ever parse [reason] to recover it.
      */
-    data class Failed(val reason: String) : SourceResult
+    data class Failed(val reason: String, val kind: FailureKind = FailureKind.TRANSPORT) : SourceResult
+
+    companion object {
+        /**
+         * Maps a thrown [IOException] to a specific failure. Both clients call this
+         * so they can never disagree, and so a new exception type gets classified
+         * once rather than twice.
+         *
+         * Measured against the live Open Library API on 2026-09-09 (30 requests):
+         * every observed failure was a TLS-stage `Connection reset by peer`, and all
+         * four came back in under 2.5s while successful requests took a median of
+         * 4.3s. Failures are cheap and fast; that asymmetry is the whole reason
+         * retrying is worth doing, and why the timeouts are set as generously as
+         * they are in `AppContainer.metadataHttpClient`.
+         *
+         * Order matters: [SocketTimeoutException] is an [InterruptedIOException] and
+         * [SSLHandshakeException] is an [SSLException], so the specific arms come
+         * first. OkHttp reports a blown `callTimeout` as a bare
+         * [InterruptedIOException], which is why that arm exists at all.
+         */
+        fun fromException(e: IOException): Failed = when (e) {
+            is SocketTimeoutException -> Failed("timeout", FailureKind.TIMEOUT)
+            is InterruptedIOException -> Failed("timeout", FailureKind.TIMEOUT)
+            is UnknownHostException -> Failed("dns lookup failed", FailureKind.TRANSPORT)
+            is SSLHandshakeException -> Failed("tls handshake failed", FailureKind.TRANSPORT)
+            is SSLException -> Failed("tls connection reset", FailureKind.TRANSPORT)
+            is ConnectException -> Failed("connection refused", FailureKind.TRANSPORT)
+            is SocketException -> Failed("connection reset", FailureKind.TRANSPORT)
+            else -> Failed("network error (${e.javaClass.simpleName})", FailureKind.TRANSPORT)
+        }
+
+        /**
+         * Maps a non-2xx HTTP status to a specific failure. 429 is called out
+         * separately from the rest of 4xx because it is the one client error that is
+         * about us rather than about the request, and because it is currently
+         * Google Books' permanent state — see docs/METADATA-SOURCES.md.
+         */
+        fun fromHttpCode(code: Int): Failed = when {
+            code == 429 -> Failed("http 429 (rate limited)", FailureKind.RATE_LIMITED)
+            code in 500..599 -> Failed("http $code (server error)", FailureKind.SERVER_ERROR)
+            else -> Failed("http $code", FailureKind.CLIENT_ERROR)
+        }
+    }
 }

app/app/src/main/java/org/modg/bookshelf/data/prefs/SettingsStore.kt

@@ -26,6 +26,7 @@ class SettingsStore(private val context: Context) {
         val USER_ID = stringPreferencesKey("user_id")
         val USER_EMAIL = stringPreferencesKey("user_email")
         val LAST_SYNC_TIME = longPreferencesKey("last_sync_time")
+        val LAST_SHELF_ID = stringPreferencesKey("last_shelf_id")
         fun cursor(collection: String) = stringPreferencesKey("cursor_$collection")
     }
 
@@ -35,6 +36,13 @@ class SettingsStore(private val context: Context) {
     val userEmail: Flow<String?> = context.dataStore.data.map { it[Keys.USER_EMAIL] }
     val lastSyncTime: Flow<Long?> = context.dataStore.data.map { it[Keys.LAST_SYNC_TIME] }
 
+    /**
+     * The shelf most recently assigned to a book — SPEC "remember the most recently
+     * used shelf" (shelving a box of books usually means one shelf, over and over).
+     * Never written for "Not shelved"; see [SettingsStore] callers.
+     */
+    val lastShelfId: Flow<String?> = context.dataStore.data.map { it[Keys.LAST_SHELF_ID] }
+
     fun cursorFor(collection: String): Flow<String?> =
         context.dataStore.data.map { it[Keys.cursor(collection)] }
 
@@ -62,12 +70,25 @@ class SettingsStore(private val context: Context) {
         context.dataStore.edit { it[Keys.LAST_SYNC_TIME] = epochMillis }
     }
 
-    /** Sign out: drop the token/user identity but keep the server URL — no need to re-enter it. */
+    suspend fun setLastShelfId(shelfId: String) {
+        context.dataStore.edit { it[Keys.LAST_SHELF_ID] = shelfId }
+    }
+
+    suspend fun clearLastShelfId() {
+        context.dataStore.edit { it.remove(Keys.LAST_SHELF_ID) }
+    }
+
+    /**
+     * Sign out: drop the token/user identity but keep the server URL — no need to
+     * re-enter it. Also drops the remembered shelf: a shared library's other
+     * account shouldn't have its shelving habit leak into this one's session.
+     */
     suspend fun clearAuth() {
         context.dataStore.edit {
             it.remove(Keys.AUTH_TOKEN)
             it.remove(Keys.USER_ID)
             it.remove(Keys.USER_EMAIL)
+            it.remove(Keys.LAST_SHELF_ID)
         }
     }
 

app/app/src/main/java/org/modg/bookshelf/ui/components/ShelfPickerSheet.kt

@@ -0,0 +1,180 @@
+package org.modg.bookshelf.ui.components
+
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.verticalScroll
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.outlined.Check
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.ModalBottomSheet
+import androidx.compose.material3.Text
+import androidx.compose.material3.rememberModalBottomSheetState
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.text.font.FontStyle
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import org.modg.bookshelf.data.local.BookcaseEntity
+import org.modg.bookshelf.data.local.ShelfEntity
+
+/**
+ * The grouped shelf picker shared by the scan screen's save sheet and the
+ * detail screen's location picker. Replaces the old flat "Bookcase • Shelf"
+ * [androidx.compose.material3.DropdownMenu] — which stopped being usable once
+ * a library had more than a couple of bookcases — with a scrolling
+ * [ModalBottomSheet] grouped one section per bookcase. A bookcase is not
+ * itself a place a book can sit, so its header is a non-selectable label;
+ * only the shelves listed under it are choices.
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun ShelfPickerSheet(
+    bookcases: List<BookcaseEntity>,
+    shelves: List<ShelfEntity>,
+    selectedShelfId: String?,
+    recentShelfId: String?,
+    onShelfSelected: (String?) -> Unit,
+    onDismissRequest: () -> Unit,
+) {
+    ModalBottomSheet(onDismissRequest = onDismissRequest, sheetState = rememberModalBottomSheetState()) {
+        ShelfPickerContent(
+            bookcases = bookcases,
+            shelves = shelves,
+            selectedShelfId = selectedShelfId,
+            recentShelfId = recentShelfId,
+            onShelfSelected = { shelfId ->
+                onShelfSelected(shelfId)
+                onDismissRequest()
+            },
+        )
+    }
+}
+
+/**
+ * The picker's contents, split out from [ShelfPickerSheet] so it can be rendered
+ * directly (Paparazzi has no real Window/scrim behind a headless [ModalBottomSheet],
+ * same problem [org.modg.bookshelf.ui.screens.ScanScreenPaparazziTest]'s class doc
+ * describes for the camera preview). Internal rather than private so that test can
+ * reach it.
+ */
+@Composable
+internal fun ShelfPickerContent(
+    bookcases: List<BookcaseEntity>,
+    shelves: List<ShelfEntity>,
+    selectedShelfId: String?,
+    recentShelfId: String?,
+    onShelfSelected: (String?) -> Unit,
+) {
+    val recent = resolveRecentShelf(recentShelfId, shelves, bookcases)
+    val recentShelf = recent?.first
+    val recentBookcase = recent?.second
+
+    Column(
+        modifier = Modifier
+            .fillMaxWidth()
+            .verticalScroll(rememberScrollState())
+            .padding(horizontal = 16.dp, vertical = 8.dp),
+    ) {
+        // Omitted entirely when there is no remembered shelf, or it no longer exists
+        // (deleted since it was last used) — a dangling "Recent" entry would be worse
+        // than no shortcut at all.
+        if (recentShelf != null && recentBookcase != null) {
+            SectionHeader(text = "Recent")
+            ShelfRow(
+                label = "${recentBookcase.name} • ${recentShelf.label}",
+                selected = selectedShelfId == recentShelf.id,
+                onClick = { onShelfSelected(recentShelf.id) },
+            )
+            GoldDivider(modifier = Modifier.padding(vertical = 12.dp))
+        }
+
+        ShelfRow(
+            label = "Not shelved",
+            selected = selectedShelfId == null,
+            onClick = { onShelfSelected(null) },
+        )
+
+        bookcases.sortedBy { it.position }.forEach { bookcase ->
+            GoldDivider(modifier = Modifier.padding(vertical = 12.dp))
+            SectionHeader(text = bookcase.name)
+            val bookcaseShelves = shelves.filter { it.bookcaseId == bookcase.id }.sortedBy { it.position }
+            if (bookcaseShelves.isEmpty()) {
+                // So an empty bookcase reads as "no shelves yet", not a rendering bug.
+                Text(
+                    text = "No shelves yet",
+                    style = MaterialTheme.typography.bodyMedium,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    fontStyle = FontStyle.Italic,
+                    modifier = Modifier.padding(vertical = 8.dp),
+                )
+            } else {
+                bookcaseShelves.forEach { shelf ->
+                    ShelfRow(
+                        label = shelf.label,
+                        selected = selectedShelfId == shelf.id,
+                        onClick = { onShelfSelected(shelf.id) },
+                    )
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun SectionHeader(text: String) {
+    Text(
+        text = text,
+        style = MaterialTheme.typography.titleSmall,
+        color = MaterialTheme.colorScheme.onSurfaceVariant,
+        modifier = Modifier.padding(top = 8.dp, bottom = 4.dp),
+    )
+}
+
+@Composable
+private fun ShelfRow(label: String, selected: Boolean, onClick: () -> Unit) {
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .clickable(onClick = onClick)
+            .padding(vertical = 12.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        Text(
+            text = label,
+            style = MaterialTheme.typography.bodyLarge,
+            fontWeight = if (selected) FontWeight.Bold else FontWeight.Normal,
+            color = if (selected) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.onSurface,
+            modifier = Modifier.weight(1f),
+        )
+        if (selected) {
+            Icon(
+                imageVector = Icons.Outlined.Check,
+                contentDescription = null,
+                tint = MaterialTheme.colorScheme.primary,
+            )
+        }
+    }
+}
+
+/**
+ * Resolves [recentShelfId] to the shelf + bookcase it names, or null when there is
+ * nothing remembered, or the remembered shelf was deleted since — the two cases the
+ * "Recent" section must be omitted for. Pure so it's directly unit-testable without
+ * standing up Compose.
+ */
+internal fun resolveRecentShelf(
+    recentShelfId: String?,
+    shelves: List<ShelfEntity>,
+    bookcases: List<BookcaseEntity>,
+): Pair<ShelfEntity, BookcaseEntity>? {
+    val shelf = recentShelfId?.let { id -> shelves.find { it.id == id } } ?: return null
+    val bookcase = bookcases.find { it.id == shelf.bookcaseId } ?: return null
+    return shelf to bookcase
+}

app/app/src/main/java/org/modg/bookshelf/ui/detail/DetailScreen.kt

@@ -19,8 +19,6 @@ import androidx.compose.material.icons.outlined.ExpandLess
 import androidx.compose.material.icons.outlined.ExpandMore
 import androidx.compose.material.icons.outlined.LocationOn
 import androidx.compose.material.icons.outlined.Save
-import androidx.compose.material3.DropdownMenu
-import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
@@ -56,6 +54,7 @@ import org.modg.bookshelf.ui.components.BookCover
 import org.modg.bookshelf.ui.components.BookshelfScaffold
 import org.modg.bookshelf.ui.components.GoldDivider
 import org.modg.bookshelf.ui.components.PaperSurface
+import org.modg.bookshelf.ui.components.ShelfPickerSheet
 
 /**
  * SPEC.md "detail" screen. [book] filters `deleted = 0`, so once the user
@@ -76,6 +75,7 @@ fun DetailScreen(
                 DetailViewModel(
                     bookRepository = container.bookRepository,
                     locationRepository = container.locationRepository,
+                    settingsStore = container.settingsStore,
                     bookId = bookId,
                 )
             }
@@ -85,6 +85,7 @@ fun DetailScreen(
     val book by viewModel.book.collectAsState()
     val bookcases by viewModel.bookcases.collectAsState()
     val shelves by viewModel.shelves.collectAsState()
+    val recentShelfId by viewModel.recentShelfId.collectAsState()
 
     var retainedBook by remember { mutableStateOf<BookEntity?>(null) }
     LaunchedEffect(book) { book?.let { retainedBook = it } }
@@ -163,6 +164,7 @@ fun DetailScreen(
                             book = display,
                             bookcases = bookcases,
                             shelves = shelves,
+                            recentShelfId = recentShelfId,
                             onShelfSelected = viewModel::saveLocation,
                         )
                     }
@@ -271,9 +273,10 @@ internal fun LocationSection(
     book: BookEntity,
     bookcases: List<BookcaseEntity>,
     shelves: List<ShelfEntity>,
+    recentShelfId: String?,
     onShelfSelected: (String?) -> Unit,
 ) {
-    var menuExpanded by remember { mutableStateOf(false) }
+    var pickerOpen by remember { mutableStateOf(false) }
     val currentShelf = shelves.find { it.id == book.shelfId }
     val currentBookcase = currentShelf?.let { shelf -> bookcases.find { it.id == shelf.bookcaseId } }
     val label = if (currentShelf != null && currentBookcase != null) {
@@ -291,24 +294,19 @@ internal fun LocationSection(
         ) {
             Icon(Icons.Outlined.LocationOn, contentDescription = null, tint = MaterialTheme.colorScheme.secondary)
             Text(text = label, style = MaterialTheme.typography.bodyLarge, modifier = Modifier.weight(1f))
-            Box {
+            TextButton(onClick = { pickerOpen = true }) { Text("Change") }
-                TextButton(onClick = { menuExpanded = true }) { Text("Change") }
+        }
-                DropdownMenu(expanded = menuExpanded, onDismissRequest = { menuExpanded = false }) {
+    }
-                    DropdownMenuItem(
+
-                        text = { Text("Not shelved") },
+    if (pickerOpen) {
-                        onClick = { onShelfSelected(null); menuExpanded = false },
+        ShelfPickerSheet(
+            bookcases = bookcases,
+            shelves = shelves,
+            selectedShelfId = book.shelfId,
+            recentShelfId = recentShelfId,
+            onShelfSelected = onShelfSelected,
+            onDismissRequest = { pickerOpen = false },
         )
-                    bookcases.forEach { bookcase ->
-                        shelves.filter { it.bookcaseId == bookcase.id }.forEach { shelf ->
-                            DropdownMenuItem(
-                                text = { Text("${bookcase.name} • ${shelf.label}") },
-                                onClick = { onShelfSelected(shelf.id); menuExpanded = false },
-                            )
-                        }
-                    }
-                }
-            }
-        }
     }
 }
 

app/app/src/main/java/org/modg/bookshelf/ui/detail/DetailViewModel.kt

@@ -9,6 +9,7 @@ import kotlinx.coroutines.launch
 import org.modg.bookshelf.data.local.BookEntity
 import org.modg.bookshelf.data.local.BookcaseEntity
 import org.modg.bookshelf.data.local.ShelfEntity
+import org.modg.bookshelf.data.prefs.SettingsStore
 import org.modg.bookshelf.data.repo.BookRepository
 import org.modg.bookshelf.data.repo.LocationRepository
 import org.modg.bookshelf.data.repo.decodeAuthors
@@ -44,6 +45,7 @@ data class BookEditForm(
 class DetailViewModel(
     private val bookRepository: BookRepository,
     private val locationRepository: LocationRepository,
+    private val settingsStore: SettingsStore,
     private val bookId: String,
 ) : ViewModel() {
 
@@ -61,6 +63,10 @@ class DetailViewModel(
     val shelves: StateFlow<List<ShelfEntity>> = locationRepository.observeShelves()
         .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), emptyList())
 
+    /** The shelf most recently assigned to any book, across sessions — surfaced as the picker's "Recent" shortcut. */
+    val recentShelfId: StateFlow<String?> = settingsStore.lastShelfId
+        .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), null)
+
     fun saveNotes(notes: String) {
         val current = book.value ?: return
         viewModelScope.launch { bookRepository.save(current.copy(notes = notes.ifBlank { null })) }
@@ -68,7 +74,17 @@ class DetailViewModel(
 
     fun saveLocation(shelfId: String?) {
         val current = book.value ?: return
-        viewModelScope.launch { bookRepository.save(current.copy(shelfId = shelfId)) }
+        viewModelScope.launch { performSaveLocation(current, shelfId) }
+    }
+
+    /**
+     * The actual save-location logic, split out from [saveLocation] so tests can await it
+     * directly (as a plain suspend call) instead of racing [viewModelScope]'s launch.
+     */
+    internal suspend fun performSaveLocation(current: BookEntity, shelfId: String?) {
+        bookRepository.save(current.copy(shelfId = shelfId))
+        // "Not shelved" (null) must never overwrite the memory — it isn't a shelf.
+        if (shelfId != null) settingsStore.setLastShelfId(shelfId)
     }
 
     fun saveEdit(form: BookEditForm) {

app/app/src/main/java/org/modg/bookshelf/ui/library/LibraryScreen.kt

@@ -18,7 +18,6 @@ import androidx.compose.material.icons.outlined.QrCodeScanner
 import androidx.compose.material.icons.outlined.Search
 import androidx.compose.material.icons.outlined.Settings
 import androidx.compose.material.icons.outlined.Sort
-import androidx.compose.material.icons.outlined.Warehouse
 import androidx.compose.material3.DropdownMenu
 import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -37,6 +36,7 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.painterResource
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
@@ -44,6 +44,7 @@ import androidx.lifecycle.viewmodel.compose.viewModel
 import androidx.lifecycle.viewmodel.initializer
 import androidx.lifecycle.viewmodel.viewModelFactory
 import org.modg.bookshelf.AppContainer
+import org.modg.bookshelf.R
 import org.modg.bookshelf.data.local.BookEntity
 import org.modg.bookshelf.data.local.BookcaseEntity
 import org.modg.bookshelf.data.local.ShelfEntity
@@ -97,7 +98,7 @@ fun LibraryScreen(
         title = "Bookshelf",
         actions = {
             IconButton(onClick = onLocationsClick) {
-                Icon(Icons.Outlined.Warehouse, contentDescription = "Bookcases & shelves")
+                Icon(painterResource(R.drawable.ic_shelves), contentDescription = "Bookcases & shelves")
             }
             IconButton(onClick = onSettingsClick) {
                 Icon(Icons.Outlined.Settings, contentDescription = "Settings")
@@ -202,6 +203,13 @@ internal fun LibraryToolbar(
                 Icon(Icons.Outlined.FilterList, contentDescription = "Filter by bookcase or shelf")
             }
             DropdownMenu(expanded = filterMenuExpanded, onDismissRequest = { filterMenuExpanded = false }) {
+                if (bookcases.isEmpty() && shelves.isEmpty()) {
+                    DropdownMenuItem(
+                        text = { Text("Add a bookcase to enable filtering") },
+                        enabled = false,
+                        onClick = {},
+                    )
+                } else {
                     DropdownMenuItem(
                         text = { Text("All books") },
                         onClick = { onFilterChange(LibraryFilter.All); filterMenuExpanded = false },
@@ -220,6 +228,7 @@ internal fun LibraryToolbar(
                     }
                 }
             }
+        }
 
         Column {
             IconButton(onClick = { sortMenuExpanded = true }) {

app/app/src/main/java/org/modg/bookshelf/ui/locations/LocationsScreen.kt

@@ -32,12 +32,15 @@ import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
 import androidx.lifecycle.viewmodel.initializer
@@ -94,7 +97,12 @@ fun LocationsScreen(
                     action = { PrimaryButton(text = "Add a bookcase", onClick = viewModel::openAddBookcase) },
                 )
             } else {
-                LazyColumn(contentPadding = PaddingValues(bottom = 96.dp)) {
+                LazyColumn(
+                    contentPadding = PaddingValues(
+                        top = innerPadding.calculateTopPadding(),
+                        bottom = innerPadding.calculateBottomPadding() + 96.dp,
+                    ),
+                ) {
                     items(state.bookcases, key = { it.bookcase.id }) { bookcaseUi ->
                         BookcaseRow(
                             bookcaseUi = bookcaseUi,
@@ -268,12 +276,22 @@ private fun BookcaseEditDialog(
 ) {
     var name by remember { mutableStateOf(editing?.name.orEmpty()) }
     var note by remember { mutableStateOf(editing?.note.orEmpty()) }
+    val nameFocusRequester = remember { FocusRequester() }
+    LaunchedEffect(Unit) {
+        runCatching { nameFocusRequester.requestFocus() }
+    }
     AlertDialog(
         onDismissRequest = onDismiss,
         title = { Text(text = title, style = MaterialTheme.typography.titleLarge) },
         text = {
             Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
-                OutlinedTextField(value = name, onValueChange = { name = it }, label = { Text("Name") }, singleLine = true)
+                OutlinedTextField(
+                    value = name,
+                    onValueChange = { name = it },
+                    label = { Text("Name") },
+                    singleLine = true,
+                    modifier = Modifier.focusRequester(nameFocusRequester),
+                )
                 OutlinedTextField(value = note, onValueChange = { note = it }, label = { Text("Note (optional)") }, singleLine = true)
             }
         },
@@ -292,11 +310,21 @@ private fun ShelfEditDialog(
     onSubmit: (label: String) -> Unit,
 ) {
     var label by remember { mutableStateOf(editing?.label.orEmpty()) }
+    val labelFocusRequester = remember { FocusRequester() }
+    LaunchedEffect(Unit) {
+        runCatching { labelFocusRequester.requestFocus() }
+    }
     AlertDialog(
         onDismissRequest = onDismiss,
         title = { Text(text = title, style = MaterialTheme.typography.titleLarge) },
         text = {
-            OutlinedTextField(value = label, onValueChange = { label = it }, label = { Text("Label") }, singleLine = true)
+            OutlinedTextField(
+                value = label,
+                onValueChange = { label = it },
+                label = { Text("Label") },
+                singleLine = true,
+                modifier = Modifier.focusRequester(labelFocusRequester),
+            )
         },
         confirmButton = {
             TextButton(onClick = { onSubmit(label) }, enabled = label.isNotBlank()) { Text("Save") }

app/app/src/main/java/org/modg/bookshelf/ui/scan/ScanScreen.kt

@@ -44,7 +44,10 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
 import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.platform.LocalSoftwareKeyboardController
 import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.platform.LocalLifecycleOwner
 import androidx.compose.ui.unit.dp
@@ -66,6 +69,7 @@ import org.modg.bookshelf.ui.components.BookshelfScaffold
 import org.modg.bookshelf.ui.components.EmptyState
 import org.modg.bookshelf.ui.components.PrimaryButton
 import org.modg.bookshelf.ui.components.SecondaryButton
+import org.modg.bookshelf.ui.components.ShelfPickerSheet
 
 /**
  * SPEC.md "scan" screen: camera + reticle, on-hit bottom sheet, continuous
@@ -85,6 +89,7 @@ fun ScanScreen(
                     bookRepository = container.bookRepository,
                     locationRepository = container.locationRepository,
                     metadataRepository = container.metadataRepository,
+                    settingsStore = container.settingsStore,
                 )
             }
         },
@@ -97,6 +102,7 @@ fun ScanScreen(
     val bookcases by viewModel.bookcases.collectAsState()
     val shelves by viewModel.shelves.collectAsState()
     val selectedShelfId by viewModel.selectedShelfId.collectAsState()
+    val recentShelfId by viewModel.recentShelfId.collectAsState()
 
     val permissionState = rememberPermissionState(Manifest.permission.CAMERA)
     LaunchedEffect(Unit) {
@@ -159,6 +165,7 @@ fun ScanScreen(
                 bookcases = bookcases,
                 shelves = shelves,
                 selectedShelfId = selectedShelfId,
+                recentShelfId = recentShelfId,
                 onShelfSelected = viewModel::selectShelf,
                 onSave = { viewModel.save(state.isbn13, state.metadata) },
                 onSkip = { viewModel.skip() },
@@ -174,6 +181,7 @@ fun ScanScreen(
                 bookcases = bookcases,
                 shelves = shelves,
                 selectedShelfId = selectedShelfId,
+                recentShelfId = recentShelfId,
                 onShelfSelected = viewModel::selectShelf,
                 onSave = { title, authors -> viewModel.saveManualEntry(state.isbn13, title, authors) },
                 onSkip = { viewModel.skip() },
@@ -185,6 +193,7 @@ fun ScanScreen(
         ) {
             LookupFailedSheet(
                 isbn13 = state.isbn13,
+                reason = state.reason,
                 onRetry = { viewModel.retryLookup(state.isbn13) },
                 onEnterByHand = { viewModel.enterByHand(state.isbn13) },
                 onSkip = { viewModel.skip() },
@@ -260,9 +269,8 @@ internal fun ScanReticle(modifier: Modifier = Modifier) {
 
 /**
  * Shown the moment a barcode is decoded, while the metadata lookup runs. It names
- * the ISBN it read and says so in words, because a lone spinner reads as "still
+ * the ISBN it read, because a lone spinner reads as "still working on it" — echoing
- * working on it" — the user goes on holding the book up to the camera when the
+ * the number back is what tells the user the barcode was actually recognised.
- * camera is already done with it.
  */
 @Composable
 internal fun SearchingSheet(isbn13: String) {
@@ -283,12 +291,6 @@ internal fun SearchingSheet(isbn13: String) {
             color = MaterialTheme.colorScheme.onSurfaceVariant,
             modifier = Modifier.padding(top = 4.dp),
         )
-        Text(
-            text = "Barcode read — you can lower the book.",
-            style = MaterialTheme.typography.bodySmall,
-            color = MaterialTheme.colorScheme.onSurfaceVariant,
-            modifier = Modifier.padding(top = 12.dp),
-        )
     }
 }
 
@@ -321,6 +323,7 @@ internal fun FoundBookSheet(
     bookcases: List<BookcaseEntity>,
     shelves: List<ShelfEntity>,
     selectedShelfId: String?,
+    recentShelfId: String?,
     onShelfSelected: (String?) -> Unit,
     onSave: () -> Unit,
     onSkip: () -> Unit,
@@ -353,6 +356,7 @@ internal fun FoundBookSheet(
             bookcases = bookcases,
             shelves = shelves,
             selectedShelfId = selectedShelfId,
+            recentShelfId = recentShelfId,
             onShelfSelected = onShelfSelected,
         )
         Row(modifier = Modifier.fillMaxWidth().padding(top = 16.dp), horizontalArrangement = Arrangement.spacedBy(12.dp)) {
@@ -375,6 +379,7 @@ internal fun ManualEntrySheet(
     bookcases: List<BookcaseEntity>,
     shelves: List<ShelfEntity>,
     selectedShelfId: String?,
+    recentShelfId: String?,
     onShelfSelected: (String?) -> Unit,
     onSave: (title: String, authors: List<String>) -> Unit,
     onSkip: () -> Unit,
@@ -409,6 +414,7 @@ internal fun ManualEntrySheet(
             bookcases = bookcases,
             shelves = shelves,
             selectedShelfId = selectedShelfId,
+            recentShelfId = recentShelfId,
             onShelfSelected = onShelfSelected,
         )
         Row(modifier = Modifier.fillMaxWidth().padding(top = 16.dp), horizontalArrangement = Arrangement.spacedBy(12.dp)) {
@@ -429,11 +435,15 @@ internal fun ManualEntrySheet(
  * Shown when a lookup couldn't be completed — SPEC: "a retry affordance, with
  * manual entry as the escape hatch; it must NOT claim the book is unknown." No
  * shelf picker here: saving isn't offered from this sheet, only a path onward to
- * one that does (Retry, or the manual-entry form via "Enter by hand").
+ * one that does (Retry, or the manual-entry form via "Enter by hand"). [reason]
+ * is [MetadataRepository]'s diagnostic string (e.g. "open library: network error;
+ * google books: http 429") — the only channel we have back from a lookup failure
+ * on a real phone, so it must actually reach the screen instead of being dropped.
  */
 @Composable
 internal fun LookupFailedSheet(
     isbn13: String,
+    reason: String,
     onRetry: () -> Unit,
     onEnterByHand: () -> Unit,
     onSkip: () -> Unit,
@@ -445,7 +455,13 @@ internal fun LookupFailedSheet(
                 "This doesn't mean the book is unknown.",
             style = MaterialTheme.typography.bodyMedium,
             color = MaterialTheme.colorScheme.onSurfaceVariant,
-            modifier = Modifier.padding(top = 8.dp, bottom = 16.dp),
+            modifier = Modifier.padding(top = 8.dp),
+        )
+        Text(
+            text = reason,
+            style = MaterialTheme.typography.bodySmall,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            modifier = Modifier.padding(top = 4.dp, bottom = 16.dp),
         )
         PrimaryButton(text = "Retry", onClick = onRetry, modifier = Modifier.fillMaxWidth())
         Row(modifier = Modifier.fillMaxWidth().padding(top = 12.dp), horizontalArrangement = Arrangement.spacedBy(12.dp)) {
@@ -478,9 +494,10 @@ internal fun ShelfPicker(
     bookcases: List<BookcaseEntity>,
     shelves: List<ShelfEntity>,
     selectedShelfId: String?,
+    recentShelfId: String?,
     onShelfSelected: (String?) -> Unit,
 ) {
-    var expanded by remember { mutableStateOf(false) }
+    var pickerOpen by remember { mutableStateOf(false) }
     val currentShelf = shelves.find { it.id == selectedShelfId }
     val currentBookcase = currentShelf?.let { shelf -> bookcases.find { it.id == shelf.bookcaseId } }
     val label = if (currentShelf != null && currentBookcase != null) {
@@ -490,21 +507,18 @@ internal fun ShelfPicker(
     }
 
     Box(modifier = Modifier.padding(top = 12.dp)) {
-        SecondaryButton(text = label, onClick = { expanded = true })
+        SecondaryButton(text = label, onClick = { pickerOpen = true })
-        androidx.compose.material3.DropdownMenu(expanded = expanded, onDismissRequest = { expanded = false }) {
+    }
-            androidx.compose.material3.DropdownMenuItem(
+
-                text = { Text("Not shelved") },
+    if (pickerOpen) {
-                onClick = { onShelfSelected(null); expanded = false },
+        ShelfPickerSheet(
+            bookcases = bookcases,
+            shelves = shelves,
+            selectedShelfId = selectedShelfId,
+            recentShelfId = recentShelfId,
+            onShelfSelected = onShelfSelected,
+            onDismissRequest = { pickerOpen = false },
         )
-            bookcases.forEach { bookcase ->
-                shelves.filter { it.bookcaseId == bookcase.id }.forEach { shelf ->
-                    androidx.compose.material3.DropdownMenuItem(
-                        text = { Text("${bookcase.name} • ${shelf.label}") },
-                        onClick = { onShelfSelected(shelf.id); expanded = false },
-                    )
-                }
-            }
-        }
     }
 }
 
@@ -517,6 +531,14 @@ private fun ManualIsbnDialog(onDismiss: () -> Unit, onSubmit: (String) -> Unit)
     // screen was just rebuilt to eliminate.
     val isbn13 = remember(text) { IsbnUtils.toIsbn13(text) }
     val malformed = text.isNotBlank() && isbn13 == null
+    val focusRequester = remember { FocusRequester() }
+    val keyboardController = LocalSoftwareKeyboardController.current
+    // The dialog opens with the field unfocused otherwise — this is the only entry
+    // point into the field, so make it ready to type into immediately.
+    LaunchedEffect(Unit) {
+        runCatching { focusRequester.requestFocus() }
+        keyboardController?.show()
+    }
     AlertDialog(
         onDismissRequest = onDismiss,
         title = { Text("Enter ISBN") },
@@ -529,6 +551,7 @@ private fun ManualIsbnDialog(onDismiss: () -> Unit, onSubmit: (String) -> Unit)
                     singleLine = true,
                     isError = malformed,
                     keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
+                    modifier = Modifier.focusRequester(focusRequester),
                 )
                 if (malformed) {
                     Text(

app/app/src/main/java/org/modg/bookshelf/ui/scan/ScanViewModel.kt

@@ -15,6 +15,7 @@ import org.modg.bookshelf.data.local.ShelfEntity
 import org.modg.bookshelf.data.metadata.BookMetadata
 import org.modg.bookshelf.data.metadata.IsbnUtils
 import org.modg.bookshelf.data.metadata.MetadataRepository
+import org.modg.bookshelf.data.prefs.SettingsStore
 import org.modg.bookshelf.data.repo.BookRepository
 import org.modg.bookshelf.data.repo.LocationRepository
 
@@ -28,6 +29,7 @@ class ScanViewModel(
     private val bookRepository: BookRepository,
     locationRepository: LocationRepository,
     private val metadataRepository: MetadataRepository,
+    private val settingsStore: SettingsStore,
     val scannerController: ScannerController = ScannerController(),
 ) : ViewModel() {
 
@@ -51,6 +53,10 @@ class ScanViewModel(
     private val _selectedShelfId = MutableStateFlow<String?>(null)
     val selectedShelfId: StateFlow<String?> = _selectedShelfId.asStateFlow()
 
+    /** The shelf most recently assigned to any book, across sessions — surfaced as the picker's "Recent" shortcut. */
+    val recentShelfId: StateFlow<String?> = settingsStore.lastShelfId
+        .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), null)
+
     init {
         viewModelScope.launch {
             scannerController.scanResults.collect { isbn13 -> onScanned(isbn13) }
@@ -104,7 +110,15 @@ class ScanViewModel(
 
     /** Save from a successful metadata lookup. */
     fun save(isbn13: String, metadata: BookMetadata) {
-        viewModelScope.launch {
+        viewModelScope.launch { performSave(isbn13, metadata) }
+    }
+
+    /**
+     * The actual save-from-metadata logic, split out from [save] so tests can await it
+     * directly (as a plain suspend call) instead of racing [viewModelScope]'s launch.
+     */
+    internal suspend fun performSave(isbn13: String, metadata: BookMetadata) {
+        val shelfId = _selectedShelfId.value
         bookRepository.createBook(
             title = metadata.title ?: "Untitled",
             subtitle = metadata.subtitle,
@@ -116,23 +130,33 @@ class ScanViewModel(
             pageCount = metadata.pageCount,
             description = metadata.description,
             coverSourceUrl = metadata.coverUrl,
-                shelfId = _selectedShelfId.value,
+            shelfId = shelfId,
         )
+        rememberShelf(shelfId)
         recordSave()
     }
-    }
 
     /** Save from the manual-entry form shown when metadata lookup misses (SPEC: pre-filled with the scanned ISBN). */
     fun saveManualEntry(isbn13: String, title: String, authors: List<String>) {
-        viewModelScope.launch {
+        viewModelScope.launch { performSaveManualEntry(isbn13, title, authors) }
+    }
+
+    /** Same split as [performSave], for [saveManualEntry]. */
+    internal suspend fun performSaveManualEntry(isbn13: String, title: String, authors: List<String>) {
+        val shelfId = _selectedShelfId.value
         bookRepository.createBook(
             title = title.ifBlank { "Untitled" },
             authors = authors,
             isbn13 = isbn13,
-                shelfId = _selectedShelfId.value,
+            shelfId = shelfId,
         )
+        rememberShelf(shelfId)
         recordSave()
     }
+
+    /** "Not shelved" (null) must never overwrite the memory — it isn't a shelf. */
+    private suspend fun rememberShelf(shelfId: String?) {
+        if (shelfId != null) settingsStore.setLastShelfId(shelfId)
     }
 
     private fun recordSave() {

app/app/src/main/res/drawable/ic_shelves.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Material Symbols "shelves" (Apache 2.0). Source viewBox is
+     "0 -960 960 960"; Android has no viewport origin, so the group
+     translate is load-bearing. Do not flatten it. -->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="960"
+    android:viewportHeight="960">
+    <group android:translateY="960">
+        <path
+            android:fillColor="#FF000000"
+            android:pathData="M120-40v-880h80v80h560v-80h80v880h-80v-80H200v80h-80Zm80-480h80v-160h240v160h240v-240H200v240Zm0 320h240v-160h240v160h80v-240H200v240Zm160-320h80v-80h-80v80Zm160 320h80v-80h-80v80Z" />
+    </group>
+</vector>

app/app/src/test/java/org/modg/bookshelf/data/metadata/GoogleBooksClientTest.kt

@@ -66,25 +66,25 @@ class GoogleBooksClientTest {
     @Test
     fun `classify reports Failed for a 404`() {
         val result = client.classify(404, null)
-        assertEquals(SourceResult.Failed("http 404"), result)
+        assertEquals(SourceResult.Failed("http 404", FailureKind.CLIENT_ERROR), result)
     }
 
     @Test
     fun `classify reports Failed for a 429 keyless-quota response, distinctly from NotFound`() {
         val result = client.classify(429, null)
-        assertEquals(SourceResult.Failed("http 429"), result)
+        assertEquals(SourceResult.Failed("http 429 (rate limited)", FailureKind.RATE_LIMITED), result)
     }
 
     @Test
     fun `classify reports Failed for a 500`() {
         val result = client.classify(500, "Internal Server Error")
-        assertEquals(SourceResult.Failed("http 500"), result)
+        assertEquals(SourceResult.Failed("http 500 (server error)", FailureKind.SERVER_ERROR), result)
     }
 
     @Test
     fun `classify reports Failed for a malformed body even on a 2xx status`() {
         val result = client.classify(200, fixture("malformed.json"))
-        assertEquals(SourceResult.Failed("malformed json"), result)
+        assertEquals(SourceResult.Failed("malformed json", FailureKind.MALFORMED), result)
     }
 
     private fun fixture(name: String): String =

app/app/src/test/java/org/modg/bookshelf/data/metadata/OpenLibraryClientTest.kt

@@ -125,25 +125,25 @@ class OpenLibraryClientTest {
     @Test
     fun `classify reports Failed for a 404`() {
         val result = client.classify(404, null, "9780201558029")
-        assertEquals(SourceResult.Failed("http 404"), result)
+        assertEquals(SourceResult.Failed("http 404", FailureKind.CLIENT_ERROR), result)
     }
 
     @Test
     fun `classify reports Failed for a 429, distinctly from NotFound`() {
         val result = client.classify(429, null, "9780201558029")
-        assertEquals(SourceResult.Failed("http 429"), result)
+        assertEquals(SourceResult.Failed("http 429 (rate limited)", FailureKind.RATE_LIMITED), result)
     }
 
     @Test
     fun `classify reports Failed for a 500`() {
         val result = client.classify(500, "Internal Server Error", "9780201558029")
-        assertEquals(SourceResult.Failed("http 500"), result)
+        assertEquals(SourceResult.Failed("http 500 (server error)", FailureKind.SERVER_ERROR), result)
     }
 
     @Test
     fun `classify reports Failed for a malformed body even on a 2xx status`() {
         val result = client.classify(200, fixture("malformed.json"), "9780201558029")
-        assertEquals(SourceResult.Failed("malformed json"), result)
+        assertEquals(SourceResult.Failed("malformed json", FailureKind.MALFORMED), result)
     }
 
     private fun fixture(name: String): String =

app/app/src/test/java/org/modg/bookshelf/data/metadata/RetryPolicyTest.kt

@@ -0,0 +1,191 @@
+package org.modg.bookshelf.data.metadata
+
+import java.io.IOException
+import java.io.InterruptedIOException
+import java.net.ConnectException
+import java.net.SocketException
+import java.net.SocketTimeoutException
+import java.net.UnknownHostException
+import javax.net.ssl.SSLException
+import javax.net.ssl.SSLHandshakeException
+import kotlin.random.Random
+import kotlinx.coroutines.test.runTest
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Covers the retry decision and the loop that acts on it. Every case is driven by
+ * the 2026-09-09 measurement of the live Open Library API recorded in
+ * docs/METADATA-SOURCES.md: fast transient TLS resets (worth repeating) against a
+ * slow but usually-successful long tail (not worth repeating).
+ *
+ * The loop is exercised with an injected clock and sleep, so these assert the real
+ * policy constants with no wall-clock time and no flakiness.
+ */
+class RetryPolicyTest {
+
+    private val transport = SourceResult.Failed("tls connection reset", FailureKind.TRANSPORT)
+    private val found = SourceResult.Found(BookMetadata(title = "Dune"))
+
+    // --- which failures are worth repeating ---
+
+    @Test
+    fun `transport and server errors are retryable`() {
+        assertTrue(RetryPolicy.isRetryable(FailureKind.TRANSPORT))
+        assertTrue(RetryPolicy.isRetryable(FailureKind.SERVER_ERROR))
+    }
+
+    @Test
+    fun `a timeout is not retried -- its budget is already spent`() {
+        assertFalse(RetryPolicy.isRetryable(FailureKind.TIMEOUT))
+    }
+
+    @Test
+    fun `a rate limit is not retried -- hammering a quota is how a block becomes permanent`() {
+        assertFalse(RetryPolicy.isRetryable(FailureKind.RATE_LIMITED))
+    }
+
+    @Test
+    fun `deterministic failures are not retried`() {
+        assertFalse(RetryPolicy.isRetryable(FailureKind.CLIENT_ERROR))
+        assertFalse(RetryPolicy.isRetryable(FailureKind.MALFORMED))
+    }
+
+    // --- the loop ---
+
+    @Test
+    fun `a first-attempt success is returned without retrying`() = runTest {
+        var calls = 0
+        val result = withRetry(sleep = {}) { calls++; found }
+        assertEquals(found, result)
+        assertEquals(1, calls)
+    }
+
+    @Test
+    fun `a transient failure followed by success returns the success`() = runTest {
+        var calls = 0
+        val result = withRetry(sleep = {}) {
+            calls++
+            if (calls == 1) transport else found
+        }
+        assertEquals(found, result)
+        assertEquals(2, calls)
+    }
+
+    @Test
+    fun `retrying stops at MAX_ATTEMPTS and reports how many were made`() = runTest {
+        var calls = 0
+        val result = withRetry(sleep = {}) { calls++; transport }
+        assertEquals(RetryPolicy.MAX_ATTEMPTS, calls)
+        // The attempt count is the whole diagnostic value of the string on a real
+        // phone: one reset and three in a row are different network stories.
+        assertEquals(
+            SourceResult.Failed("tls connection reset, 3 attempts", FailureKind.TRANSPORT),
+            result,
+        )
+    }
+
+    @Test
+    fun `a single failure is reported without an attempt count`() = runTest {
+        val timeout = SourceResult.Failed("timeout", FailureKind.TIMEOUT)
+        var calls = 0
+        val result = withRetry(sleep = {}) { calls++; timeout }
+        assertEquals(1, calls)
+        assertEquals(timeout, result)
+    }
+
+    @Test
+    fun `NotFound is authoritative and is never retried`() = runTest {
+        var calls = 0
+        val result = withRetry(sleep = {}) { calls++; SourceResult.NotFound }
+        assertEquals(SourceResult.NotFound, result)
+        assertEquals(1, calls)
+    }
+
+    @Test
+    fun `an un-retryable failure short-circuits after one attempt`() = runTest {
+        var calls = 0
+        val result = withRetry(sleep = {}) { calls++; SourceResult.fromHttpCode(429) }
+        assertEquals(1, calls)
+        assertEquals(FailureKind.RATE_LIMITED, (result as SourceResult.Failed).kind)
+    }
+
+    @Test
+    fun `the budget stops a new attempt but never cancels one in flight`() = runTest {
+        // Clock jumps past the budget during the first attempt. The result of that
+        // attempt must still be honoured, and no second attempt may start.
+        var now = 0L
+        var calls = 0
+        val result = withRetry(
+            budgetMillis = 1_000L,
+            nowMillis = { now },
+            sleep = {},
+        ) {
+            calls++
+            now += 5_000L
+            transport
+        }
+        assertEquals(1, calls)
+        assertEquals(transport, result)
+    }
+
+    @Test
+    fun `backoff is short and jittered, never zero and never seconds long`() {
+        val r = Random(1234)
+        repeat(200) {
+            val first = RetryPolicy.backoffMillis(2, r)
+            val second = RetryPolicy.backoffMillis(3, r)
+            assertTrue("first retry backoff was $first", first in 250L..349L)
+            assertTrue("second retry backoff was $second", second in 750L..1049L)
+        }
+    }
+
+    // --- exception and status classification ---
+
+    @Test
+    fun `socket timeout and a blown call timeout both classify as TIMEOUT`() {
+        assertEquals(FailureKind.TIMEOUT, SourceResult.fromException(SocketTimeoutException()).kind)
+        // OkHttp reports an exceeded callTimeout as a bare InterruptedIOException.
+        assertEquals(FailureKind.TIMEOUT, SourceResult.fromException(InterruptedIOException()).kind)
+    }
+
+    @Test
+    fun `the observed live failure -- a TLS-stage reset -- classifies as retryable transport`() {
+        val failed = SourceResult.fromException(SSLException("Connection reset by peer"))
+        assertEquals(FailureKind.TRANSPORT, failed.kind)
+        assertTrue(RetryPolicy.isRetryable(failed.kind))
+    }
+
+    @Test
+    fun `each transport exception gets its own reason, not a generic one`() {
+        // The reason string is the only diagnostic we get back from a real phone,
+        // so these must stay distinguishable from each other.
+        val reasons = listOf(
+            SourceResult.fromException(UnknownHostException()).reason,
+            SourceResult.fromException(SSLHandshakeException("h")).reason,
+            SourceResult.fromException(SSLException("r")).reason,
+            SourceResult.fromException(ConnectException()).reason,
+            SourceResult.fromException(SocketException()).reason,
+        )
+        assertEquals(reasons.size, reasons.toSet().size)
+        assertTrue(reasons.none { it.isBlank() })
+    }
+
+    @Test
+    fun `an unrecognised IOException names its own type rather than saying network error`() {
+        val failed = SourceResult.fromException(IOException("boom"))
+        assertEquals(FailureKind.TRANSPORT, failed.kind)
+        assertTrue(failed.reason, failed.reason.contains("IOException"))
+    }
+
+    @Test
+    fun `http statuses map to the kinds that drive retrying`() {
+        assertEquals(FailureKind.RATE_LIMITED, SourceResult.fromHttpCode(429).kind)
+        assertEquals(FailureKind.SERVER_ERROR, SourceResult.fromHttpCode(500).kind)
+        assertEquals(FailureKind.SERVER_ERROR, SourceResult.fromHttpCode(503).kind)
+        assertEquals(FailureKind.CLIENT_ERROR, SourceResult.fromHttpCode(404).kind)
+        assertEquals(FailureKind.CLIENT_ERROR, SourceResult.fromHttpCode(400).kind)
+    }
+}

app/app/src/test/java/org/modg/bookshelf/data/prefs/SettingsStoreTest.kt

@@ -0,0 +1,73 @@
+package org.modg.bookshelf.data.prefs
+
+import androidx.test.core.app.ApplicationProvider
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.test.runTest
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/**
+ * Covers the "remember the most recently used shelf" feature's persistence layer —
+ * see [org.modg.bookshelf.ui.scan.ScanViewModel] and
+ * [org.modg.bookshelf.ui.detail.DetailViewModel] for the callers that decide *when*
+ * to write, and [org.modg.bookshelf.ui.components.resolveRecentShelf] for how the
+ * picker decides whether the remembered shelf is still offerable.
+ */
+@RunWith(RobolectricTestRunner::class)
+@Config(sdk = [34])
+class SettingsStoreTest {
+
+    private lateinit var settingsStore: SettingsStore
+
+    @Before
+    fun setUp() = runTest {
+        settingsStore = SettingsStore(ApplicationProvider.getApplicationContext())
+        // DataStore's backing file lives in the app's real files dir, which Robolectric
+        // does not reset between test methods in this class — start every test from a
+        // known-clean slate instead of depending on method execution order.
+        settingsStore.clearLastShelfId()
+    }
+
+    @Test
+    fun `last shelf id is null before anything is remembered`() = runTest {
+        assertNull(settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `last shelf id round-trips through the store`() = runTest {
+        settingsStore.setLastShelfId("sh-top")
+
+        assertEquals("sh-top", settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `setting a new last shelf id overwrites the previous one`() = runTest {
+        settingsStore.setLastShelfId("sh-top")
+        settingsStore.setLastShelfId("sh-desk")
+
+        assertEquals("sh-desk", settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `clearLastShelfId drops the remembered shelf`() = runTest {
+        settingsStore.setLastShelfId("sh-top")
+
+        settingsStore.clearLastShelfId()
+
+        assertNull(settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `sign out clears the remembered shelf so it can't leak to the other account`() = runTest {
+        settingsStore.setLastShelfId("sh-top")
+
+        settingsStore.clearAuth()
+
+        assertNull(settingsStore.lastShelfId.first())
+    }
+}

app/app/src/test/java/org/modg/bookshelf/ui/components/ShelfPickerSheetPaparazziTest.kt

@@ -0,0 +1,78 @@
+package org.modg.bookshelf.ui.components
+
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import app.cash.paparazzi.DeviceConfig
+import app.cash.paparazzi.Paparazzi
+import org.junit.Rule
+import org.junit.Test
+import org.modg.bookshelf.data.local.BookcaseEntity
+import org.modg.bookshelf.data.local.ShelfEntity
+import org.modg.bookshelf.data.local.SyncState
+import org.modg.bookshelf.ui.theme.BookshelfTheme
+
+/**
+ * [ShelfPickerSheet]'s grouped picker, replacing the old flat dropdown (SPEC
+ * task: "the state the whole change exists for"). Renders [ShelfPickerContent]
+ * directly rather than the real [androidx.compose.material3.ModalBottomSheet] —
+ * Paparazzi has no real Window/scrim behind a headless sheet, same problem
+ * [org.modg.bookshelf.ui.screens.ScanScreenPaparazziTest]'s class doc describes.
+ * Two bookcases, one of them empty, plus a remembered "Recent" shelf — the
+ * state this whole component exists for.
+ */
+class ShelfPickerSheetPaparazziTest {
+
+    @get:Rule
+    val paparazzi = Paparazzi(deviceConfig = DeviceConfig.PIXEL_6)
+
+    private val livingRoom = BookcaseEntity(
+        id = "bc-living-room", name = "Living Room", note = null, position = 0,
+        createdAt = 1, updatedAt = 1, syncState = SyncState.SYNCED,
+    )
+    private val study = BookcaseEntity(
+        id = "bc-study", name = "Study", note = null, position = 1,
+        createdAt = 1, updatedAt = 1, syncState = SyncState.SYNCED,
+    )
+    private val topShelf = ShelfEntity(
+        id = "sh-top", bookcaseId = livingRoom.id, label = "Top shelf — fiction", position = 0,
+        createdAt = 1, updatedAt = 1, syncState = SyncState.SYNCED,
+    )
+    private val bottomShelf = ShelfEntity(
+        id = "sh-bottom", bookcaseId = livingRoom.id, label = "Bottom shelf — reference", position = 1,
+        createdAt = 1, updatedAt = 1, syncState = SyncState.SYNCED,
+    )
+
+    @Test
+    fun shelfPickerGroupedLight() = snapshotBoth("shelf-picker-grouped") {
+        Content()
+    }
+
+    @Composable
+    private fun Content() = Shell {
+        ShelfPickerContent(
+            bookcases = listOf(livingRoom, study), // "study" has no shelves yet — empty-bookcase state
+            shelves = listOf(topShelf, bottomShelf),
+            selectedShelfId = bottomShelf.id,
+            recentShelfId = topShelf.id, // recent shelf, distinct from the current selection
+            onShelfSelected = {},
+        )
+    }
+
+    @Composable
+    private fun Shell(content: @Composable () -> Unit) {
+        Box(modifier = Modifier.fillMaxWidth()) {
+            Surface(color = MaterialTheme.colorScheme.surface) {
+                content()
+            }
+        }
+    }
+
+    private fun snapshotBoth(name: String, content: @Composable () -> Unit) {
+        paparazzi.snapshot(name = "$name-light") { BookshelfTheme(darkTheme = false) { content() } }
+        paparazzi.snapshot(name = "$name-dark") { BookshelfTheme(darkTheme = true) { content() } }
+    }
+}

app/app/src/test/java/org/modg/bookshelf/ui/components/ShelfPickerSheetTest.kt

@@ -0,0 +1,53 @@
+package org.modg.bookshelf.ui.components
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+import org.modg.bookshelf.data.local.BookcaseEntity
+import org.modg.bookshelf.data.local.ShelfEntity
+import org.modg.bookshelf.data.local.SyncState
+
+/**
+ * [resolveRecentShelf] backs [ShelfPickerSheet]'s "Recent" section: it must be
+ * omitted, not shown dangling, when there is nothing remembered or the
+ * remembered shelf no longer exists (deleted since it was last used).
+ */
+class ShelfPickerSheetTest {
+
+    private val livingRoom = BookcaseEntity(
+        id = "bc-living-room", name = "Living Room", note = null, position = 0,
+        createdAt = 1, updatedAt = 1, syncState = SyncState.SYNCED,
+    )
+    private val topShelf = ShelfEntity(
+        id = "sh-top", bookcaseId = livingRoom.id, label = "Top shelf", position = 0,
+        createdAt = 1, updatedAt = 1, syncState = SyncState.SYNCED,
+    )
+
+    @Test
+    fun `no remembered shelf resolves to null`() {
+        val result = resolveRecentShelf(recentShelfId = null, shelves = listOf(topShelf), bookcases = listOf(livingRoom))
+
+        assertNull(result)
+    }
+
+    @Test
+    fun `a remembered shelf that no longer exists resolves to null`() {
+        val result = resolveRecentShelf(recentShelfId = "sh-deleted", shelves = listOf(topShelf), bookcases = listOf(livingRoom))
+
+        assertNull(result)
+    }
+
+    @Test
+    fun `a remembered shelf whose bookcase was deleted resolves to null`() {
+        val result = resolveRecentShelf(recentShelfId = topShelf.id, shelves = listOf(topShelf), bookcases = emptyList())
+
+        assertNull(result)
+    }
+
+    @Test
+    fun `a remembered shelf that still exists resolves to its shelf and bookcase`() {
+        val result = resolveRecentShelf(recentShelfId = topShelf.id, shelves = listOf(topShelf), bookcases = listOf(livingRoom))
+
+        assertEquals(topShelf to livingRoom, result)
+    }
+}

app/app/src/test/java/org/modg/bookshelf/ui/detail/DetailViewModelTest.kt

@@ -0,0 +1,77 @@
+package org.modg.bookshelf.ui.detail
+
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.test.runTest
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.modg.bookshelf.data.local.BookEntity
+import org.modg.bookshelf.data.local.BookshelfDatabase
+import org.modg.bookshelf.data.prefs.SettingsStore
+import org.modg.bookshelf.data.repo.BookRepository
+import org.modg.bookshelf.data.repo.LocationRepository
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/**
+ * SPEC's "remember the most recently used shelf" from the detail screen's side:
+ * [DetailViewModel.saveLocation] must write a non-null shelf to [SettingsStore],
+ * but "Not shelved" (null) must never overwrite what's already remembered.
+ */
+@RunWith(RobolectricTestRunner::class)
+@Config(sdk = [34])
+class DetailViewModelTest {
+
+    private lateinit var db: BookshelfDatabase
+    private lateinit var settingsStore: SettingsStore
+    private lateinit var viewModel: DetailViewModel
+    private lateinit var book: BookEntity
+    private lateinit var shelfId: String
+
+    @Before
+    fun setUp() = runTest {
+        val context = ApplicationProvider.getApplicationContext<android.content.Context>()
+        db = Room.inMemoryDatabaseBuilder(context, BookshelfDatabase::class.java)
+            .allowMainThreadQueries()
+            .build()
+        settingsStore = SettingsStore(context)
+        val bookRepository = BookRepository(db.bookDao(), context)
+        val locationRepository = LocationRepository(db.bookcaseDao(), db.shelfDao(), db.bookDao())
+        val bookcaseId = locationRepository.createBookcase(name = "Living Room")
+        shelfId = locationRepository.createShelf(bookcaseId, label = "Top shelf")
+        val bookId = bookRepository.createBook(title = "Piranesi")
+        book = checkNotNull(bookRepository.getById(bookId))
+
+        viewModel = DetailViewModel(
+            bookRepository = bookRepository,
+            locationRepository = locationRepository,
+            settingsStore = settingsStore,
+            bookId = bookId,
+        )
+    }
+
+    @After
+    fun tearDown() {
+        db.close()
+    }
+
+    @Test
+    fun `moving a book to a shelf remembers that shelf`() = runTest {
+        viewModel.performSaveLocation(book, shelfId)
+
+        assertEquals(shelfId, settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `marking a book Not shelved does not overwrite the remembered shelf`() = runTest {
+        settingsStore.setLastShelfId(shelfId)
+
+        viewModel.performSaveLocation(book, null)
+
+        assertEquals(shelfId, settingsStore.lastShelfId.first())
+    }
+}

app/app/src/test/java/org/modg/bookshelf/ui/scan/ScanViewModelTest.kt

@@ -0,0 +1,100 @@
+package org.modg.bookshelf.ui.scan
+
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.test.runTest
+import kotlinx.serialization.json.Json
+import okhttp3.OkHttpClient
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.modg.bookshelf.data.local.BookshelfDatabase
+import org.modg.bookshelf.data.metadata.BookMetadata
+import org.modg.bookshelf.data.metadata.MetadataRepository
+import org.modg.bookshelf.data.prefs.SettingsStore
+import org.modg.bookshelf.data.repo.BookRepository
+import org.modg.bookshelf.data.repo.LocationRepository
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/**
+ * SPEC's "remember the most recently used shelf": [ScanViewModel.save] and
+ * [ScanViewModel.saveManualEntry] must write the chosen shelf to [SettingsStore]
+ * so it survives to the next scanning session — except "Not shelved" (null),
+ * which must never overwrite what's already remembered.
+ */
+@RunWith(RobolectricTestRunner::class)
+@Config(sdk = [34])
+class ScanViewModelTest {
+
+    private lateinit var db: BookshelfDatabase
+    private lateinit var settingsStore: SettingsStore
+    private lateinit var viewModel: ScanViewModel
+    private lateinit var locationRepository: LocationRepository
+    private lateinit var shelfId: String
+
+    @Before
+    fun setUp() = runTest {
+        val context = ApplicationProvider.getApplicationContext<android.content.Context>()
+        db = Room.inMemoryDatabaseBuilder(context, BookshelfDatabase::class.java)
+            .allowMainThreadQueries()
+            .build()
+        settingsStore = SettingsStore(context)
+        locationRepository = LocationRepository(db.bookcaseDao(), db.shelfDao(), db.bookDao())
+        val bookcaseId = locationRepository.createBookcase(name = "Living Room")
+        shelfId = locationRepository.createShelf(bookcaseId, label = "Top shelf")
+
+        viewModel = ScanViewModel(
+            bookRepository = BookRepository(db.bookDao(), context),
+            locationRepository = locationRepository,
+            metadataRepository = MetadataRepository(OkHttpClient(), Json { ignoreUnknownKeys = true }),
+            settingsStore = settingsStore,
+        )
+    }
+
+    @After
+    fun tearDown() {
+        db.close()
+    }
+
+    @Test
+    fun `saving a metadata hit to a shelf remembers that shelf`() = runTest {
+        viewModel.selectShelf(shelfId)
+
+        viewModel.performSave("9780765326355", BookMetadata(title = "The Way of Kings"))
+
+        assertEquals(shelfId, settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `saving a manual entry to a shelf remembers that shelf`() = runTest {
+        viewModel.selectShelf(shelfId)
+
+        viewModel.performSaveManualEntry("9780765326355", "The Way of Kings", listOf("Brandon Sanderson"))
+
+        assertEquals(shelfId, settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `saving as Not shelved does not overwrite the remembered shelf`() = runTest {
+        settingsStore.setLastShelfId(shelfId)
+        viewModel.selectShelf(null)
+
+        viewModel.performSave("9780765326355", BookMetadata(title = "The Way of Kings"))
+
+        assertEquals(shelfId, settingsStore.lastShelfId.first())
+    }
+
+    @Test
+    fun `saving a manual entry as Not shelved does not overwrite the remembered shelf`() = runTest {
+        settingsStore.setLastShelfId(shelfId)
+        viewModel.selectShelf(null)
+
+        viewModel.performSaveManualEntry("9780765326355", "The Way of Kings", emptyList())
+
+        assertEquals(shelfId, settingsStore.lastShelfId.first())
+    }
+}

app/app/src/test/java/org/modg/bookshelf/ui/screens/DetailScreenPaparazziTest.kt

@@ -78,6 +78,7 @@ class DetailScreenPaparazziTest {
                         book = book,
                         bookcases = ScreenFixtures.bookcases,
                         shelves = ScreenFixtures.shelves,
+                        recentShelfId = null,
                         onShelfSelected = {},
                     )
                 }

app/app/src/test/java/org/modg/bookshelf/ui/screens/LocationsScreenPaparazziTest.kt

@@ -18,6 +18,7 @@ import app.cash.paparazzi.DeviceConfig
 import app.cash.paparazzi.Paparazzi
 import org.junit.Rule
 import org.junit.Test
+import org.modg.bookshelf.data.local.BookcaseEntity
 import org.modg.bookshelf.ui.components.BookshelfScaffold
 import org.modg.bookshelf.ui.components.GoldDivider
 import org.modg.bookshelf.ui.components.PaperSurface
@@ -40,12 +41,25 @@ class LocationsScreenPaparazziTest {
     @Test
     fun locationsPopulatedLight() = snapshotBoth("locations-populated") { Populated() }
 
-    @Composable
+    /**
-    private fun Populated() = Shell()
+     * Regression coverage for the ghost-bookcase bug: with the list branch not
+     * folding in the Scaffold's top app bar inset, a single bookcase's row
+     * rendered underneath the app bar and was invisible. This renders exactly
+     * that one-bookcase state; check the recorded PNG shows the bookcase row
+     * fully below the app bar, not clipped/hidden behind it.
+     */
+    @Test
+    fun locationsSingleBookcaseLight() = snapshotBoth("locations-single-bookcase") { SingleBookcase() }
 
     @Composable
-    private fun Shell() {
+    private fun Populated() = Shell(ScreenFixtures.bookcases)
-        val bookcaseUis = ScreenFixtures.bookcases.map { bookcase ->
+
+    @Composable
+    private fun SingleBookcase() = Shell(listOf(ScreenFixtures.livingRoom))
+
+    @Composable
+    private fun Shell(bookcases: List<BookcaseEntity>) {
+        val bookcaseUis = bookcases.map { bookcase ->
             BookcaseUi(
                 bookcase = bookcase,
                 shelves = ScreenFixtures.shelves

app/app/src/test/java/org/modg/bookshelf/ui/screens/ScanScreenPaparazziTest.kt

@@ -96,6 +96,7 @@ class ScanScreenPaparazziTest {
                     bookcases = ScreenFixtures.bookcases,
                     shelves = ScreenFixtures.shelves,
                     selectedShelfId = ScreenFixtures.deskShelf.id,
+                    recentShelfId = null,
                     onShelfSelected = {},
                     onSave = {},
                     onSkip = {},
@@ -127,6 +128,7 @@ class ScanScreenPaparazziTest {
             ) {
                 LookupFailedSheet(
                     isbn13 = "9780765326355",
+                    reason = "open library: network error; google books: http 429",
                     onRetry = {},
                     onEnterByHand = {},
                     onSkip = {},

docs/HANDOFF.md

@@ -411,3 +411,90 @@ successfully. Use these instead, in this order:
   2. `tail logs/<name>.state` — says SUCCESS / GIVING UP / WALL CLOCK explicitly.
   3. `git status --porcelain` — is there actually work in the tree?
 The sentinel is a convenience, not the record of truth. `logs/<name>.state` is.
+
+## Wave 6 — second on-device feedback round: COMPLETE, verified 2026-09-09
+The user tested the phone build again and sent eight items. All eight are done.
+Two Sonnet workers (`tasks/H1-screens.txt`, `tasks/H2-picker.txt`) took the UI
+work; the ORCHESTRATOR did the retry/backoff work itself in `data/metadata` and
+`AppContainer`, because it needed the live measurement below to design it.
+
+| Check | Result |
+|---|---|
+| `./tasks/gw assembleDebug` | exit 0 |
+| `./tasks/gw testDebugUnitTest` | exit 0 — **172 tests**, 1 skipped, 0 failures (was 138) |
+| `./tasks/gw verifyPaparazziDebug` | exit 0 |
+| `grep "always 'false'"` on a `--rerun-tasks` rebuild | **0 hits** |
+| `./tasks/gw assembleRelease` | exit 0 — 41,810,740 bytes, V2 signer `CN=Bookshelf, O=Montanaro` |
+| boundary check | clean — neither worker touched a build file or the other's packages |
+
+### The ghost bookcase was an inset bug, not a data bug
+`LocationsScreen`'s list branch dropped the Scaffold's `innerPadding` while its
+empty-state branch applied it, so the FIRST bookcase row rendered underneath the
+top app bar and was invisible. Every symptom the user described follows from that:
+invisible first bookcase, no empty state on re-entry (the list was genuinely
+non-empty), a second bookcase created, both showing in the filter menu. **Both
+records were always real and healthy** — the user should delete the spare.
+Every other screen was checked for the same class of bug; Locations was the only
+one. Fix: fold `innerPadding` into the LazyColumn's `contentPadding` (NOT
+`Modifier.padding`, which would clip the scroll area instead of insetting it).
+
+### Metadata: measured, not guessed
+See `docs/METADATA-SOURCES.md` § "Measured again 2026-09-09" for the full data.
+Two things that change how you should think about this app:
+
+1. **Google Books keyless is dead for everyone, permanently.** The user's
+   residential-IP test returned a quota error naming `project_number:624717413613`
+   — a shared anonymous *project*, not an IP. The old note in METADATA-SOURCES.md
+   guessing that a residential IP "may well get answers" is now marked CORRECTED
+   in place. Because `combine()` turns any Failed-with-no-Found into `Unavailable`,
+   this standing failure meant **every** Open Library hiccup surfaced as
+   "one or more sources couldn't be reached". The app has been single-sourced all
+   along. **The user has deliberately deferred the API key — do not add it unasked.**
+2. **Our own timeouts were manufacturing failures.** 30 live requests: 13% failed,
+   all fast TLS resets (<2.5s); successes had a median of 4.3s but a max of 22.0s,
+   and **2 of 26 successes exceeded the old 12s `callTimeout`**. Timeouts are now
+   25s/20s/20s. Failures are fast and successes are slow, so a short timeout buys
+   nothing on the failure path and costs real successes on the slow path.
+
+`RetryPolicy` + `withRetry` (new, `data/metadata/`) retry TRANSPORT and
+SERVER_ERROR only. It deliberately does NOT retry:
+- **TIMEOUT** — the budget is already spent; retrying could triple the wait.
+- **RATE_LIMITED** — hammering a quota is how an intermittent block becomes a
+  permanent one, and METADATA-SOURCES.md records that happening to this project's
+  IP. Revisit when the Google Books key lands: a *keyed* 429 is a per-second limit
+  and does deserve one Retry-After-respecting retry.
+`SourceResult.Failed` now carries a `FailureKind` alongside its human `reason`, and
+`reason` names the specific exception ("tls connection reset, 3 attempts") instead
+of a generic "network error". **That string is now rendered on the scan sheet and
+is our ONLY diagnostic channel from a real phone.** Nothing may parse it.
+
+### Known-soft spots in wave 6 — do not mistake these for verified
+1. **The Paparazzi "regression" snapshot for the ghost bookcase is a lookalike,
+   not the real screen.** `LocationsScreenPaparazziTest` hand-rolls its own
+   Scaffold+LazyColumn copy because the real `LocationsScreen` needs an
+   `AppContainer` (Room + DataStore). The orchestrator verified the REAL fix by
+   reading the diff; the PNG only proves the test's copy is right, and the two can
+   drift — the copy already omits the bottom inset the real screen adds. Splitting
+   a stateless `LocationsContent(state, callbacks)` out of the screen would make
+   this snapshot genuine. Worth doing before anyone trusts it as regression cover.
+2. **The auto-focus calls are unverified.** Three dialogs now do
+   `LaunchedEffect(Unit) { runCatching { focusRequester.requestFocus() } }`. That
+   is the idiomatic form, but there is no emulator here and `runCatching` means a
+   too-early call fails SILENTLY rather than crashing. If a dialog opens unfocused
+   on the phone, that is why; the fix is to await a frame before requesting.
+3. **The shelf picker opens as a bottom sheet stacked on top of the save sheet**
+   (H2's own flagged judgement call). It renders correctly in Paparazzi but
+   sheet-over-sheet is awkward on real Android. Watch it on the device.
+
+### Worker lessons (both are repeats — the prompts already forbade them)
+- **H1 backgrounded a Gradle build and ended its turn**, exactly the wave-4
+  failure, despite an explicit foreground-only instruction AND
+  `CLAUDE_CODE_PRINT_BG_WAIT_CEILING_MS=0` being set in `run-task.sh`. Its final
+  message was "I'll wait for this background build to complete." `run-task.sh`
+  still recorded SUCCESS because the process exited 0. **`.state` saying SUCCESS
+  means the process exited cleanly, NOT that the worker finished its task** — read
+  `logs/<name>.summary` and check that the result is an actual report. H1's work
+  was fine, but nobody verified it except the orchestrator.
+- H2 (108 turns, $4.00) followed the brief closely, ran builds in the foreground,
+  and reported honestly, including flagging its own stacked-sheet judgement call.
+  Cost ratio to H1 ($0.66, 5 turns) is roughly the ratio of work actually done.

docs/METADATA-SOURCES.md

@@ -97,6 +97,10 @@ Worth saying plainly, because it bounds how much weight the numbers carry:
   this host sharing a quota pool with other tenants; **your phone, on a
   residential or mobile IP, may well get answers.** That's precisely why the
   app needs to be able to tell us which it got.
+  > **CORRECTED 2026-09-09 — this guess was WRONG.** The user tested from a
+  > residential IP and got the same refusal, naming a shared *project* quota
+  > rather than an IP one. See "Measured again 2026-09-09" at the end of this
+  > file. Do not act on the sentence above.
 - I don't know which three ISBNs you scanned. If you still have the books to
   hand, those three numbers are worth more than another 60 sampled ones.
 
@@ -215,3 +219,76 @@ One thing worth deciding separately: 17% of books legitimately have no cover art
 anywhere. The placeholder now looks deliberate rather than broken, but if you
 want covers on everything, that's a different feature — photograph the book,
 store it as the cover — and not a metadata-source problem at all.
+
+## Measured again 2026-09-09, after the user tested from a residential IP
+
+Two things were settled that the first round could only guess at.
+
+### Google Books keyless is dead everywhere, not just from this box
+
+The user ran the app's exact Google Books call from their home connection and got:
+
+    Quota exceeded for quota metric 'Queries' and limit 'Queries per day'
+    of service 'books.googleapis.com' for consumer 'project_number:624717413613'
+
+That names a **Google Cloud project, not an IP**. Every keyless caller on the
+internet is billed to that one shared anonymous project and its daily quota is
+exhausted. So:
+
+- The earlier caveat — "your phone, on a residential or mobile IP, may well get
+  answers" — is **WRONG**. Delete it from your mental model. It was tested and it
+  is not true.
+- Backoff cannot help. This is a daily quota, not a per-second rate limit.
+- A free API key is the only fix, and it is a complete one: it moves the app into
+  its own project with its own quota (free tier 1,000 req/day).
+
+The knock-on is the part that actually hurt the user. `MetadataRepository.combine`
+turns "any source Failed, none Found" into `Unavailable`. Google Books is a
+PERMANENT standing failure, so **every** Open Library hiccup became `Unavailable`.
+The app has effectively been single-sourced this whole time while reporting
+failures as though two sources had been consulted.
+
+**The user has deliberately deferred the API key.** Do not implement it unasked.
+
+### Open Library: 13% failure, and our own timeout was manufacturing more
+
+30 requests, the exact call `OpenLibraryClient` makes, 1.5s apart, from the sprite:
+
+| | |
+|---|---|
+| failure rate | **13%** (4 of 30) |
+| every failure | curl exit 35 — TLS-stage `Connection reset by peer` |
+| failure latency | 0.23s, 0.31s, 0.59s, 2.46s — **all fast** |
+| success latency | median **4.3s**, p75 6.0s, p90 **9.2s**, max **22.0s** |
+| successes over the old 12s callTimeout | **2 of 26 (8%)** |
+
+Two conclusions, and they point in opposite directions:
+
+1. **Failures are cheap and transient**, so retrying is nearly free. 13% → ~1.7%
+   at two attempts → ~0.2% at three. This is why `RetryPolicy` exists and why its
+   backoff is milliseconds rather than the conventional seconds.
+2. **Successes are slow and long-tailed**, and the app's own
+   `callTimeout(12s)`/`connectTimeout(10s)` were cutting off roughly 8% of
+   lookups that were about to succeed — then reporting them to the user as
+   "couldn't be reached". The app was generating a meaningful share of its own
+   failures. Timeouts are now 25s/20s/20s, above the 22.0s worst observed success.
+
+The asymmetry is the whole design: a short timeout buys nothing on the failure
+path (failures return in under 2.5s regardless) and costs real successes on the
+slow path. That is also why `RetryPolicy.isRetryable` refuses to repeat a
+TIMEOUT — a timeout means the budget was already spent, and the evidence says
+slow requests mostly succeed if you let them finish.
+
+Connection reuse is visible in the data and matters in real use: cold connects
+ran 2-19s while warm ones ran 0.07s. OkHttp pools connections for 5 minutes, so
+scanning a box of books in sequence stays on the fast path after the first book.
+
+### What still is not known
+
+- All 30 requests came from this datacenter IP. The user's phone may see a
+  different failure rate. The reason string now shown on the scan sheet
+  (`SourceResult.Failed.reason`, e.g. "tls connection reset, 3 attempts") is how
+  we find out — it is the only diagnostic channel we have from a real device.
+- The user's own 3-request sample showed 2 failures. That is consistent with 13%
+  (p ~ 5%) but does not confirm it. If their phone reports "3 attempts" often,
+  their network is worse than this one and the retry count deserves revisiting.

logs/G-diagnostics.sid

@@ -0,0 +1 @@
+9b656dc8-a225-47ec-b6ce-549241854de6

logs/G-diagnostics.summary

@@ -0,0 +1,19 @@
+=== G-diagnostics  attempts=2 quota_waits=1 hard_fails=0 ===
+cost=$0.28007899999999997 turns=6 err=?
+--- result (tail) ---
+` case. `byIsbnCoverUrl` untouched.
+
+**AppContainer.kt** — `metadataHttpClient` now has `callTimeout(12s)/connectTimeout(10s)/readTimeout(10s)`. PocketBase `okHttpClient` untouched.
+
+**ui.scan:**
+- `ScanCodeFilter.kt` — `accept()` returns `ScanOutcome { Isbn, NotAnIsbn, Ignored }`; one shared debounce mechanism throttles repeats of valid *and* rejected codes alike.
+- `ScannerController.kt` — new `rejectedCodes: SharedFlow<String>` routed alongside `scanResults`.
+- `ScanModels.kt` — `ScanSheetState.NotFound` gained `viaLookupFailure: Boolean = false`; added `ScanSheetState.LookupFailed(isbn13, reason)`; `ScanMetadataOutcome.from` maps all three `LookupResult` cases.
+- `ScanViewModel.kt` — `retryLookup`/`enterByHand` added; lookup logic factored so Retry bypasses the "sheet already showing" guard; `rejectedMessage: StateFlow<String?>` with a 3s auto-clear timer.
+- `ScanScreen.kt` — new `LookupFailedSheet` (Retry/Enter by hand/Skip, dismissible, never claims the book unknown); `ManualEntrySheet` reworded via `authoritative: Boolean`; new `RejectedBarcodeBanner` shown over the camera.
+
+**Tests:** classify() cases for both clients, the full 3×3 `combine` matrix, `ScanCodeFilter` throttle tests with an injected clock, `ScannerController` rejected-code routing, updated `ScanModelsTest`, and two new Paparazzi snapshots (`LookupFailedSheet`, rejected-barcode banner) recorded in both light and dark — all visually verified.
+
+No warnings (Kotlin or otherwise) were introduced in any file I touched; a clean `--rerun` compile shows only pre-existing, unrelated deprecation warnings elsewhere in the codebase.
+
+Nothing was left undone relative to the original instructions, and no constraints (forbidden files, no commits, foreground builds, no MockWebServer) were violated.

logs/H1-screens.sid

@@ -0,0 +1 @@
+430e1016-0c8c-47a5-905b-ad106cbb6b19

logs/H1-screens.summary

@@ -0,0 +1,4 @@
+=== H1-screens  attempts=1 quota_waits=0 hard_fails=0 ===
+cost=$0.6623552 turns=5 err=?
+--- result (tail) ---
+I'll wait for this background build to complete before continuing.

logs/H2-picker.sid

@@ -0,0 +1 @@
+67bf128a-9c53-4fd2-b9ce-10b99f4a385d

logs/H2-picker.summary

@@ -0,0 +1,10 @@
+=== H2-picker  attempts=1 quota_waits=0 hard_fails=0 ===
+cost=$3.9990499999999995 turns=108 err=?
+--- result (tail) ---
+ succeeded. New `shelf-picker-grouped-{light,dark}` snapshot shows two bookcases (Living Room with two shelves, one selected/bold/checked; Study empty with "No shelves yet"), plus the "Recent" section and "Not shelved" — verified visually. Existing `scan-searching-sheet` and `scan-lookup-failed-sheet` snapshots regenerated and confirmed correct (no stray "lower the book" line; reason string now visible).
+- Grepped all Kotlin compiler warnings from a forced rebuild: zero `always 'false'` hits anywhere, including my files.
+- `git status --porcelain`: only my owned files changed by me (`data/prefs/SettingsStore.kt`, `ui/scan/ScanScreen.kt`, `ui/scan/ScanViewModel.kt`, `ui/detail/DetailScreen.kt`, `ui/detail/DetailViewModel.kt`, new `ui/components/ShelfPickerSheet.kt`, and new/edited files under `app/app/src/test/**`). Everything else showing modified/untracked (`AppContainer.kt`, `data/metadata/**`, `ui/locations/**`, `ui/library/**`, `res/drawable/**`, `docs/METADATA-SOURCES.md`, locations snapshots) is the orchestrator's/other worker's concurrent work — untouched by me, left as-is.
+
+**Didn't do / judgment calls worth flagging**
+- Nothing skipped from the spec. One design decision: `ShelfPickerSheet` owns its own `ModalBottomSheet`, so tapping "Choose a shelf"/"Change" opens it as a second, stacked sheet over the already-open save/detail sheet — this matches "presented as a Material 3 ModalBottomSheet" literally rather than inlining the list in the existing sheet.
+- Added tests beyond the stated minimum: `SettingsStoreTest` (round-trip, overwrite, clear, clearAuth), `ShelfPickerSheetTest` (`resolveRecentShelf` — null/missing-shelf/missing-bookcase/found cases), `ScanViewModelTest` and `DetailViewModelTest` (remember-on-save/move, "Not shelved" doesn't overwrite).

logs/WAVE6-DONE

@@ -0,0 +1,14 @@
+=== WAVE6-DONE written 2026-09-09T15:31:35+00:00 ===
+Workers finished. The orchestrator was NOT necessarily alive for this.
+
+--- H1-screens ---
+[2026-09-09T15:05:30+00:00] H1-screens: SUCCESS after 1 attempt(s), 0 quota wait(s)
+cost=$0.6623552 turns=5
+
+--- H2-picker ---
+[2026-09-09T15:31:29+00:00] H2-picker: SUCCESS after 1 attempt(s), 0 quota wait(s)
+cost=$3.9990499999999995 turns=108
+
+NEXT: orchestrator must independently verify before accepting:
+  cd ~/bookshelf && ./tasks/gw assembleDebug && ./tasks/gw testDebugUnitTest
+  git status --porcelain   # boundary check: who touched what

tasks/H1-screens.txt

@@ -0,0 +1,137 @@
+You are a Sonnet worker on the Bookshelf Android app (~/bookshelf). Read
+`docs/SPEC.md` first — it is the authoritative product contract and it wins over
+anything you infer from the code. Do not restate it, do not let it drift.
+
+## Ground rules (violating these fails the wave)
+- Build ONLY with `./tasks/gw <task>` — never `./gradlew`. A second worker shares
+  this Gradle project dir and concurrent invocations clobber each other. `tasks/gw`
+  is a flock-serialized wrapper.
+- Run builds in the FOREGROUND. Never background a Gradle build and end your turn
+  saying you'll report later — `claude -p` kills background tasks and you will
+  never report at all. Builds take up to 10 minutes; just wait.
+- You own EXACTLY these files:
+      app/app/src/main/java/org/modg/bookshelf/ui/locations/LocationsScreen.kt
+      app/app/src/main/java/org/modg/bookshelf/ui/library/LibraryScreen.kt
+      app/app/src/main/res/drawable/ic_shelves.xml          (new file, create it)
+      app/app/src/test/**                                    (tests you add)
+  Touch NOTHING else. Specifically forbidden: any build file
+  (`app/build.gradle.kts`, `gradle/libs.versions.toml`, `settings.gradle.kts`),
+  `data/**`, `ui/scan/**`, `ui/detail/**`, `ui/components/**`, `ui/nav/**`,
+  `ui/settings/**`, `ui/setup/**`, `AppContainer.kt`. Another worker and the
+  orchestrator own those RIGHT NOW and are editing them concurrently.
+- Do not change any public composable signature. `ui/nav/BookshelfNavHost.kt`
+  calls these screens and you may not edit it.
+
+## Task 1 — the ghost-bookcase bug (highest priority, a real user-facing defect)
+`LocationsScreen.kt` line ~97. The Scaffold hands `content` an `innerPadding` that
+accounts for the top app bar. The empty-state branch applies it; the list branch
+does NOT:
+
+    ) { innerPadding ->
+        PaperSurface(...) {
+            if (state.bookcases.isEmpty()) {
+                EmptyState(modifier = Modifier.padding(innerPadding), ...)   // correct
+            } else {
+                LazyColumn(contentPadding = PaddingValues(bottom = 96.dp)) { // BUG
+
+So the first bookcase row renders UNDERNEATH the app bar and is invisible. A user
+created a bookcase, could not see it, created a second one, and ended up with two
+real bookcases and no idea why. Fix it by folding `innerPadding` into the
+LazyColumn's `contentPadding` so the existing 96.dp bottom inset is PRESERVED and
+added to, not replaced — the bottom inset is what keeps the last row clear of the
+FAB. Something equivalent to:
+
+    contentPadding = PaddingValues(
+        top = innerPadding.calculateTopPadding(),
+        bottom = innerPadding.calculateBottomPadding() + 96.dp,
+    )
+
+Using `contentPadding` rather than `Modifier.padding` is deliberate: it keeps the
+list scrolling under the bar instead of clipping the scroll area.
+
+VERIFY THIS SPECIFICALLY: add a Paparazzi snapshot of `LocationsScreen` in a state
+with exactly ONE bookcase, and confirm in the rendered PNG that the bookcase row is
+fully visible below the app bar. A one-bookcase list is the exact case that was
+broken and it must be the case you prove fixed. If the existing Paparazzi harness
+makes rendering this screen with seeded state impractical, say so plainly in your
+report rather than skipping it silently.
+
+## Task 2 — auto-focus the first field in the location dialogs
+In `LocationsScreen.kt`, `BookcaseEditDialog` (~line 276) and `ShelfEditDialog`
+(~line 299) each open with an unfocused `OutlinedTextField`. The first field
+should take focus and raise the keyboard when the dialog appears. Use a
+`FocusRequester` + `LaunchedEffect(Unit) { focusRequester.requestFocus() }`.
+Bookcase dialog: focus "Name" (not "Note"). Shelf dialog: focus "Label".
+Guard the requestFocus call so it cannot throw if the node isn't attached yet.
+
+## Task 3 — library filter empty state
+`LibraryScreen.kt` ~line 204. The filter DropdownMenu always offers "All books"
+first, then a flat list of bookcases and shelves. When there are NO bookcases and
+NO shelves, the menu contains only "All books" — which is already the active state
+and cannot be changed, so it is a menu with nothing in it.
+
+When `bookcases` and `shelves` are both empty, replace the menu contents with a
+single DISABLED item reading "Add a bookcase to enable filtering". Keep the
+toolbar filter icon visible and enabled (it is how the feature is discovered) —
+only the menu's contents change. When locations DO exist, behaviour is unchanged.
+
+## Task 4 — replace the Warehouse icon with a real bookcase
+`LibraryScreen.kt` line ~100 uses `Icons.Outlined.Warehouse` for the button that
+opens Locations. It renders as a barn and reads wrong. `material-icons-extended`
+1.7.8 has no bookcase glyph (I checked all 1932 outlined icons), so use Material
+Symbols' `shelves`, which is a bookcase frame with shelves and books on them.
+
+Create `app/app/src/main/res/drawable/ic_shelves.xml` with EXACTLY this content.
+This is the SVG path verbatim from Google's CDN. Do not re-derive it, do not
+    "simplify" it, and do not convert its relative (lowercase) commands to absolute
+    ones — Android's pathData parser accepts SVG syntax as-is. Material Symbols ship with
+`viewBox="0 -960 960 960"` — a negative Y origin that Android `<vector>` has no
+equivalent for — and the `<group android:translateY="960">` is what compensates.
+Removing it renders an empty icon.
+
+    <?xml version="1.0" encoding="utf-8"?>
+    <!-- Material Symbols "shelves" (Apache 2.0). Source viewBox is
+         "0 -960 960 960"; Android has no viewport origin, so the group
+         translate is load-bearing. Do not flatten it. -->
+    <vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="960"
+        android:viewportHeight="960">
+        <group android:translateY="960">
+            <path
+                android:fillColor="#FF000000"
+                android:pathData="M120-40v-880h80v80h560v-80h80v880h-80v-80H200v80h-80Zm80-480h80v-160h240v160h240v-240H200v240Zm0 320h240v-160h240v160h80v-240H200v240Zm160-320h80v-80h-80v80Zm160 320h80v-80h-80v80Z" />
+        </group>
+    </vector>
+
+Then swap the icon at the call site:
+
+    Icon(painterResource(R.drawable.ic_shelves), contentDescription = "Bookcases & shelves")
+
+Keep the existing contentDescription text. `Icon` applies its own tint over a
+Painter exactly as it does over an ImageVector, so the icon still picks up the
+theme colour — do NOT hardcode a colour at the call site. You will need imports
+for `androidx.compose.ui.res.painterResource` and `org.modg.bookshelf.R`, and the
+`Icons.Outlined.Warehouse` import becomes unused — remove it.
+
+## Verify before you report (all in the FOREGROUND)
+    ./tasks/gw assembleDebug
+    ./tasks/gw testDebugUnitTest
+    ./tasks/gw recordPaparazziDebug
+    git status --porcelain
+
+- assembleDebug and testDebugUnitTest must exit 0. The test count is 138 today and
+  must not go DOWN.
+- Grep your build output for the string `always 'false'`. That Kotlin warning class
+  silently blanked every book cover in this app for months by making a `when`
+  branch dead code that still compiled. Zero hits on files you touched.
+- `git status --porcelain` must show ONLY the files you own. If it shows others,
+  you have broken the boundary — report it, do not revert someone else's work.
+- Do not commit. The orchestrator commits after verifying.
+
+## Report
+Finish with a plain report: what you changed per task, the exact exit codes and
+test counts, whether the one-bookcase Paparazzi render actually proves task 1, and
+anything you could NOT do. Do not claim success you did not verify — several
+previous workers on this project over-claimed and were caught.

tasks/H2-picker.txt

@@ -0,0 +1,143 @@
+You are a Sonnet worker on the Bookshelf Android app (~/bookshelf). Read
+`docs/SPEC.md` first — it is the authoritative product contract and it wins over
+anything you infer from the code. Do not restate it, do not let it drift.
+
+## Ground rules (violating these fails the wave)
+- Build ONLY with `./tasks/gw <task>` — never `./gradlew`. Another worker shares
+  this Gradle project dir and concurrent invocations clobber each other.
+  `tasks/gw` is a flock-serialized wrapper.
+- Run builds in the FOREGROUND. Never background a Gradle build and end your turn
+  saying you'll report later — `claude -p` kills background tasks and you will
+  never report at all. Builds take up to 10 minutes; just wait.
+- You own EXACTLY these files:
+      ui/components/ShelfPickerSheet.kt          (new file, create it)
+      ui/scan/ScanScreen.kt
+      ui/scan/ScanViewModel.kt
+      ui/detail/DetailScreen.kt
+      ui/detail/DetailViewModel.kt
+      data/prefs/SettingsStore.kt
+      app/app/src/test/**                         (tests you add)
+  (paths relative to app/app/src/main/java/org/modg/bookshelf/)
+  Touch NOTHING else. Specifically forbidden: any build file
+  (`app/build.gradle.kts`, `gradle/libs.versions.toml`), `data/metadata/**`
+  (the ORCHESTRATOR is editing that right now, in this same working tree),
+  `ui/locations/**`, `ui/library/**`, `ui/nav/**`, `ui/settings/**`,
+  `ui/setup/**`, `AppContainer.kt`, and every file in `ui/components/` EXCEPT the
+  new `ShelfPickerSheet.kt` you create.
+- Do not change any public composable signature. `ui/nav/BookshelfNavHost.kt`
+  calls these screens and you may not edit it.
+- `AppContainer.settingsStore` is already a public val — you do NOT need to change
+  AppContainer to reach it.
+
+## Background: what the user actually reported
+They are shelving books a box at a time, scanning a run of books that all belong
+on the SAME shelf. Two complaints:
+1. The shelf dropdown lists every bookcase×shelf pair in one flat menu. With more
+   than a couple of bookcases that is unusable.
+2. Re-picking the same shelf for every book in the box is tedious.
+
+## Task 1 — a grouped shelf picker, replacing the flat dropdown
+There are currently TWO near-duplicate flat pickers:
+  - `ShelfPicker` in `ScanScreen.kt` (~line 477)
+  - the location picker inside `DetailScreen.kt` (~line 273-310)
+Both build a `DropdownMenu` containing "Not shelved" followed by one flat item per
+(bookcase, shelf) pair, labelled "Bookcase • Shelf".
+
+Replace BOTH with ONE new shared composable in `ui/components/ShelfPickerSheet.kt`,
+presented as a Material 3 `ModalBottomSheet` rather than a dropdown. Contents, top
+to bottom:
+  a. A "Recent" section — see task 2. Omit the whole section when there is no
+     remembered shelf, or when the remembered shelf no longer exists.
+  b. "Not shelved" as an always-available choice.
+  c. One section per bookcase, in `position` order. The bookcase name is a section
+     header (non-selectable — a bookcase is not a location a book can sit in;
+     only shelves are). Its shelves are listed under it in `position` order,
+     labelled with just the shelf label, since the header already gives the
+     bookcase. Make the currently-selected shelf visually distinct.
+  d. A bookcase with no shelves shows its header and an inline "No shelves yet"
+     hint, so an empty bookcase does not look like a rendering bug.
+The sheet must scroll. Do NOT add a search field — the user explicitly deferred
+that; we will add it later if the grouping alone proves insufficient.
+
+Design language is in SPEC.md ("feels like books") and the existing components in
+`ui/components/` are your reference for type, spacing and the gold hairline rules.
+Reuse `GoldDivider` for section separation rather than inventing a new rule.
+
+## Task 2 — remember the most recently used shelf
+Add a `LAST_SHELF_ID` key to `SettingsStore` (a nullable String preference, with a
+`Flow<String?>` reader, a setter, and a way to clear it), following the exact
+shape of the keys already there. Clear it in `clearAuth()` alongside the rest —
+signing out of a shared library should not leak the other account's shelf.
+
+Write it whenever a book's shelf is set to a non-null value:
+  - `ScanViewModel` — on save, both from a metadata hit and from manual entry.
+  - `DetailViewModel` — when the user changes a book's location.
+Setting a book to "Not shelved" must NOT overwrite the remembered shelf; it isn't
+a shelf, and clobbering the memory with it would defeat the whole feature.
+
+Surface it as the "Recent" section at the top of the picker, labelled with the
+full "Bookcase • Shelf" text (the section has no bookcase header to lean on).
+
+**Do NOT pre-select it.** The user considered and explicitly rejected
+pre-selection: the risk of silently mis-shelving a book, when the user forgets to
+change it, outweighs saving one tap. A new scan still starts with no shelf chosen;
+the remembered shelf is one tap away at the top of the sheet, and that is all.
+
+Note `ScanViewModel._selectedShelfId` already survives across saves within a single
+scanning session (it is deliberately not reset in `recordSave`). Keep that. What
+you are adding is persistence ACROSS sessions and screens.
+
+## Task 3 — three small fixes in ScanScreen.kt
+3a. In `SearchingSheet` (~line 268), delete the third Text, the one reading
+    "Barcode read — you can lower the book." The user says "Searching…" plus the
+    ISBN already carries it. Update the composable's KDoc, which currently
+    justifies that line — do not leave a comment explaining code that is gone.
+
+3b. `LookupFailedSheet` (~line 435) takes a `reason` parameter and never renders
+    it. `ScanSheetState.LookupFailed(isbn13, reason)` already carries a diagnostic
+    string, and `MetadataRepository` already builds it as e.g.
+    "open library: network error; google books: http 429". It is currently dead —
+    it reaches the UI and is dropped on the floor.
+    Render it, below the existing explanatory paragraph, in
+    `MaterialTheme.typography.bodySmall` and `onSurfaceVariant`. This is the only
+    diagnostic channel we have from a real phone, so it must actually appear.
+    Keep the existing headline and paragraph as they are — the reason is
+    supplementary detail, not a replacement for plain-language copy.
+    NOTE: the orchestrator is concurrently making those reason strings more
+    specific. Do not depend on their exact wording — render whatever you are
+    given, and do not parse, match on, or reformat the string.
+
+3c. `ManualIsbnDialog` (~line 512) opens with an unfocused text field. Auto-focus
+    it and raise the keyboard, via `FocusRequester` +
+    `LaunchedEffect(Unit) { focusRequester.requestFocus() }`. Guard the call so it
+    cannot throw if the node is not attached yet.
+
+## Verify before you report (all in the FOREGROUND)
+    ./tasks/gw assembleDebug
+    ./tasks/gw testDebugUnitTest
+    ./tasks/gw recordPaparazziDebug
+    git status --porcelain
+
+- assembleDebug and testDebugUnitTest must exit 0. The test count is 138 today and
+  must not go DOWN. Add real tests for the logic you introduce — at minimum the
+  SettingsStore round-trip, that "Not shelved" does not overwrite the memory, and
+  that a remembered shelf which no longer exists is not offered. Assertion-free
+  tests are explicitly forbidden by SPEC's quality bar.
+- Add a Paparazzi snapshot of the new picker sheet with at least two bookcases,
+  one of them empty, and a recent shelf present — that is the state the whole
+  change exists for, and no one has ever trusted a worker's word on how this app
+  looks.
+- Grep your build output for the string `always 'false'`. That Kotlin warning class
+  silently blanked every book cover in this app for months by making a `when`
+  branch dead code that still compiled. Zero hits on files you touched.
+- `git status --porcelain` will show files the orchestrator and the other worker
+  are editing (`data/metadata/**`, `ui/locations/**`, `ui/library/**`,
+  `res/drawable/**`). That is EXPECTED. Confirm only that no file outside your
+  own list was changed BY YOU. Never revert or "fix" someone else's work.
+- Do not commit. The orchestrator commits after verifying.
+
+## Report
+Finish with a plain report: what you changed per task, exact exit codes and test
+counts, what the new Paparazzi PNG shows, and anything you could NOT do. Do not
+claim success you did not verify — several previous workers on this project
+over-claimed and were caught.