diff --git a/app-rust/examples/phone.rs b/app-rust/examples/phone.rs
index 9985c9e..fd855df 100644
--- a/app-rust/examples/phone.rs
+++ b/app-rust/examples/phone.rs
@@ -32,17 +32,17 @@ fn typed_argv() -> Option<String> {
 }
 
 fn main() {
-    DefaultApp::<Client>::run();
+    DesktopApp::<Client>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 pub struct Client {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
     #[allow(dead_code)]
     screen: Option<ai_app::ui::TranscriptScreen>,
 }
 
-impl DefaultAppState for Client {
+impl DesktopAppState for Client {
     fn window_attributes() -> WindowAttributes {
         WindowAttributes::default()
             .with_title("iris transcript (bench fixture)")
@@ -53,8 +53,8 @@ impl DefaultAppState for Client {
     }
 
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
         let screen = match ai_app::ui::fixture::open(rsc, &mut ui_state) {
diff --git a/app-rust/examples/transcript.rs b/app-rust/examples/transcript.rs
index a33bf8a..17672df 100644
--- a/app-rust/examples/transcript.rs
+++ b/app-rust/examples/transcript.rs
@@ -3,12 +3,12 @@ use ai_app::client::transcript_fold::{QuestionCard, TranscriptItem, TranscriptRo
 use iris::prelude::*;
 
 fn main() {
-    DefaultApp::<Client>::run();
+    DesktopApp::<Client>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 pub struct Client {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
     #[allow(dead_code)]
     screen: ai_app::ui::TranscriptScreen,
 }
@@ -157,13 +157,13 @@ fn fold_event(items: Vec<Item>, seq: u64) -> Vec<Item> {
 > A quoted line, to show the bar and the indent.
 ";
 
-impl DefaultAppState for Client {
+impl DesktopAppState for Client {
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
-        let screen = ai_app::ui::build(rsc, &mut ui_state, synthetic_rows());
+        let mut screen = ai_app::ui::build(rsc, &mut ui_state, synthetic_rows());
         screen.push_row(
             rsc,
             &FoldedRow::Single(TranscriptItem::CommandRow {
diff --git a/app-rust/src/android/app_log.rs b/app-rust/src/android/app_log.rs
index 10a82ad..6442583 100644
--- a/app-rust/src/android/app_log.rs
+++ b/app-rust/src/android/app_log.rs
@@ -3,13 +3,13 @@
 //! `android_logger` as the logger to forward to and nothing else.
 
 use crate::client::log_ring::{self, LogRing};
+use std::{
+    fs, panic,
+    path::{Path, PathBuf},
+    sync::OnceLock,
+};
 
-/// Installs the ring in front of `android_logger`, so `logcat` still sees
-/// exactly what it saw before and the ring sees it too.
-///
-/// Called once, from `JNI_OnLoad`. A second call is refused by `log`
-/// itself; the message says which caller, since two initialisation paths
-/// is a programmer error rather than something to recover from.
+/// Installs the in-process ring in front of Android's logger.
 pub fn install(max_level: log::LevelFilter) {
     let inner = android_logger::AndroidLogger::new(
         android_logger::Config::default()
@@ -23,10 +23,6 @@ pub fn install(max_level: log::LevelFilter) {
     )
     .is_err()
     {
-        // Not a panic: a logger already installed means logging works,
-        // just without the ring, and taking the app down over a
-        // diagnostic would be worse than the diagnostic being missing.
-        // The line goes through whatever logger did win.
         log::warn!("iris app log: a logger was already installed, so there is no ring");
     }
     install_panic_hook();
@@ -40,9 +36,6 @@ pub fn ring() -> &'static LogRing {
 pub fn diagnostics_line() -> String {
     let where_to_read = match crate::android::devlog::authority() {
         Some(authority) => format!("devlog provider: content://{authority}"),
-        // Not "off": Android creates a provider lazily, so this is what
-        // "nobody has asked for it yet" looks like, and it is a different
-        // thing from a build that does not have one.
         None => "devlog provider: declared, not created yet".to_string(),
     };
     format!("{}\n{where_to_read}", ring().summary())
@@ -53,26 +46,17 @@ pub fn diagnostics_line() -> String {
 /// start.
 const CRASH_FILE: &str = "last-panic.txt";
 
-/// How many of the dying run's own log lines the panic hook saves with
-/// the panic, and [`set_crash_dir`] replays.
-///
-/// The panic's message and location say *what* broke; these say what the
-/// app was doing on the way there, which is the half that is otherwise
-/// unrecoverable -- the ring is memory only, so an abort takes every line
-/// before the panic with it. Bounded rather than the whole ring because
-/// this is written by a hook on a process that is about to die, and
-/// because the replay pushes each line into the new run's ring, where an
-/// unbounded paste would evict the run that is actually being watched.
+/// Enough preceding log lines to explain a crash without evicting the next run.
 const CRASH_CONTEXT_LINES: usize = 80;
 
 const PREVIOUS_RUN_TARGET: &str = "previous_run";
 
-static CRASH_PATH: std::sync::OnceLock<std::path::PathBuf> = std::sync::OnceLock::new();
+static CRASH_PATH: OnceLock<PathBuf> = OnceLock::new();
 
 /// Copies aborting panics into the device-readable log ring.
 fn install_panic_hook() {
-    let previous = std::panic::take_hook();
-    std::panic::set_hook(Box::new(move |info| {
+    let previous = panic::take_hook();
+    panic::set_hook(Box::new(move |info| {
         let where_at = match info.location() {
             Some(at) => format!("{}:{}:{}", at.file(), at.line(), at.column()),
             None => "an unknown location".to_string(),
@@ -81,41 +65,23 @@ fn install_panic_hook() {
         let line = format!("iris panic at {where_at}: {message}");
         log::error!("{line}");
         if let Some(path) = CRASH_PATH.get() {
-            // The panic line first, then what the app was doing before
-            // it: one file, split again on that first newline by
-            // `set_crash_dir`.
             let context = ring()
                 .try_tail_text(CRASH_CONTEXT_LINES)
                 .unwrap_or_else(|| {
                     "(the log ring was locked as this run died; no context)".to_string()
                 });
-            // Best effort by design: a panic is already the failure, and
-            // failing to record it must not become a second one.
-            let _ = std::fs::write(path, format!("{line}\n{context}"));
+            let _ = fs::write(path, format!("{line}\n{context}"));
         }
         previous(info);
     }));
 }
 
-/// Tells the panic hook where to leave its report, and replays the report
-/// a previous run left there into the ring before deleting it.
-///
-/// Called from **both** `MainActivity.nativeSetFilesDir` and
-/// `DevLogProvider.nativeReady` -- whichever of the two runs first in
-/// this process, since after a crash Dev Updater's query starts the
-/// process for the provider alone and no activity ever runs. Safe to call
-/// twice: the file is gone after the first, so the second finds nothing
-/// and says nothing. The panic itself is replayed at `error` level and
-/// says it is from the previous run, so a crash loop shows the reason it
-/// is looping in the Runtime tab of the run that is still up.
-pub fn set_crash_dir(dir: &std::path::Path) {
+/// Configures crash persistence and replays a report left by the previous run.
+pub fn set_crash_dir(dir: &Path) {
     let path = dir.join(CRASH_FILE);
-    if let Ok(previous) = std::fs::read_to_string(&path) {
-        // Delete before replaying rather than after: a replay that itself
-        // panicked would otherwise leave the file to be replayed again on
-        // every start, and a crash loop nothing can get out of is worse
-        // than one report lost.
-        let _ = std::fs::remove_file(&path);
+    if let Ok(previous) = fs::read_to_string(&path) {
+        // Delete first so a panic during replay cannot create a replay loop.
+        let _ = fs::remove_file(&path);
         replay_crash(&previous);
     }
     let _ = CRASH_PATH.set(path);
diff --git a/app-rust/src/android/bench_client.rs b/app-rust/src/android/bench_client.rs
index 6d9f467..15ca029 100644
--- a/app-rust/src/android/bench_client.rs
+++ b/app-rust/src/android/bench_client.rs
@@ -1,12 +1,19 @@
 use crate::android::bench_jni::PlatformHandle;
 use crate::client::transcript_fold::{TranscriptItem, fold_event};
+use crate::ui::{self, TranscriptScreen};
 use android_view::jni::{JavaVM, objects::GlobalRef};
 use event_model::SeqEvent;
 use iris::android::{AndroidAppState, AndroidRsc, AndroidUiState, HasAndroidUiState};
 use iris::prelude::*;
-use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, Mutex};
-use std::time::{Duration, Instant};
+use std::{
+    fs, mem,
+    sync::{
+        Arc, Mutex,
+        atomic::{AtomicBool, Ordering},
+        mpsc,
+    },
+    time::{Duration, Instant},
+};
 
 const STREAM_EVENTS_PER_SEC: u64 = 20;
 const STREAM_SECONDS: u64 = 20;
@@ -40,7 +47,7 @@ pub struct BenchClient {
     content: WeakWidget<WidgetPtr>,
     report_display: WeakWidget<TextEdit>,
     top_bar: WeakWidget<WidgetPtr>,
-    screen: Option<crate::ui::TranscriptScreen>,
+    screen: Option<TranscriptScreen>,
     items: Vec<TranscriptItem>,
     stream_tail: Vec<SeqEvent>,
     platform: Option<Arc<PlatformHandle>>,
@@ -80,7 +87,7 @@ fn process_cpu_ms() -> Option<u64> {
     // SAFETY: `rusage` is a plain-old-data struct `getrusage` fully
     // initialises on success; on failure it is never read.
     unsafe {
-        let mut usage: libc::rusage = std::mem::zeroed();
+        let mut usage: libc::rusage = mem::zeroed();
         if libc::getrusage(libc::RUSAGE_SELF, &mut usage) != 0 {
             return None;
         }
@@ -91,7 +98,7 @@ fn process_cpu_ms() -> Option<u64> {
 }
 
 fn peak_rss_kb() -> Option<u64> {
-    std::fs::read_to_string("/proc/self/status")
+    fs::read_to_string("/proc/self/status")
         .ok()?
         .lines()
         .find_map(|line| line.strip_prefix("VmHWM:"))
@@ -174,7 +181,7 @@ impl AndroidAppState for BenchClient {
             last_top_pad: 0.0,
         };
 
-        match crate::ui::fixture::build_screen(rsc) {
+        match ui::fixture::build_screen(rsc) {
             Ok((opened, tree)) => {
                 client.items = opened.items;
                 client.stream_tail = opened.stream_tail;
@@ -392,7 +399,7 @@ impl BenchClient {
     }
 
     fn rebuild_transcript(&mut self, rsc: &mut Rsc) {
-        let (screen, tree) = crate::ui::build_tree(rsc, crate::ui::fixture::rows(&self.items));
+        let (screen, tree) = ui::build_tree(rsc, ui::fixture::rows(&self.items));
         (self.content)(rsc).set(tree);
         self.screen = Some(screen);
     }
@@ -653,7 +660,7 @@ where
     T: Send + 'static,
     F: FnOnce(&mut BenchClient, &mut Rsc) -> T + Send + 'static,
 {
-    let (tx, rx) = std::sync::mpsc::channel();
+    let (tx, rx) = mpsc::channel();
     ctx.update(move |state: &mut BenchClient, rsc| {
         let _ = tx.send(f(state, rsc));
     });
@@ -769,7 +776,7 @@ async fn run_stream_phase(
         ctx.update(move |state: &mut BenchClient, rsc| {
             let old_items = state.items.clone();
             state.items = fold_event(&state.items, &event);
-            match &state.screen {
+            match state.screen.as_mut() {
                 Some(screen) => screen.apply(rsc, &old_items, &state.items),
                 None => state.rebuild_transcript(rsc),
             }
diff --git a/app-rust/src/android/devlog.rs b/app-rust/src/android/devlog.rs
index cc54620..6e71631 100644
--- a/app-rust/src/android/devlog.rs
+++ b/app-rust/src/android/devlog.rs
@@ -4,7 +4,7 @@
 use android_view::jni::JNIEnv;
 use android_view::jni::objects::{JClass, JObject, JString};
 use android_view::jni::sys::{jlong, jobjectArray};
-use std::sync::OnceLock;
+use std::{path::Path, ptr, sync::OnceLock};
 
 /// Gated with its one reader: the tabs demo links no `client-core` and so
 /// has no ring to lay out, and an ungated constant is a warning in that
@@ -43,7 +43,7 @@ pub extern "system" fn Java_dev_iris_android_demo_DevLogProvider_nativeReady(
 ) {
     #[cfg(feature = "transcript-screen")]
     if let Some(dir) = string_arg(&mut env, &files_dir) {
-        crate::android::app_log::set_crash_dir(std::path::Path::new(&dir));
+        crate::android::app_log::set_crash_dir(Path::new(&dir));
     }
     #[cfg(not(feature = "transcript-screen"))]
     let _ = &files_dir;
@@ -138,7 +138,7 @@ fn line_fields(_since: u64) -> Vec<String> {
 /// down to report that its diagnostic is unavailable would be worse than
 /// the diagnostic being unavailable.
 fn string_array(env: &mut JNIEnv, fields: &[String]) -> jobjectArray {
-    let null = std::ptr::null_mut();
+    let null = ptr::null_mut();
     let Ok(class) = env.find_class("java/lang/String") else {
         return null;
     };
diff --git a/app-rust/src/android/mod.rs b/app-rust/src/android/mod.rs
index 42d3059..af29da9 100644
--- a/app-rust/src/android/mod.rs
+++ b/app-rust/src/android/mod.rs
@@ -10,7 +10,10 @@ use android_view::{
 #[cfg(not(feature = "transcript-screen"))]
 use iris::android::{AndroidAppState, AndroidRsc, AndroidUiState, HasAndroidUiState};
 use log::LevelFilter;
-use std::ffi::c_void;
+use std::{
+    ffi::c_void,
+    path::{Path, PathBuf},
+};
 
 /// The app's own log ring and its upload -- only where `client-core` is
 /// linked, which is every build that has a server to send to. The plain
@@ -50,7 +53,7 @@ impl HasAndroidUiState for Client {
 impl AndroidAppState for Client {
     fn new(mut ui_state: AndroidUiState, rsc: &mut AndroidRsc<Self>) -> Self {
         // `widgets.info` is the winit example's frame-debug readout, kept
-        // current from `DefaultAppState::window_event` -- android-view has
+        // current from `DesktopAppState::window_event` -- android-view has
         // no per-frame hook to drive the equivalent from here yet, so it
         // is left at its built "" text rather than wired to nothing.
         let _ = tabs_ui::build(rsc, &mut ui_state);
@@ -123,8 +126,8 @@ pub extern "system" fn Java_dev_iris_android_demo_MainActivity_nativeSetFilesDir
     };
     #[cfg(feature = "transcript-screen")]
     {
-        app_log::set_crash_dir(std::path::Path::new(&dir));
-        enrollment::set_files_dir(std::path::PathBuf::from(&dir));
+        app_log::set_crash_dir(Path::new(&dir));
+        enrollment::set_files_dir(PathBuf::from(&dir));
     }
     log::debug!("iris app: files directory is {dir}");
 }
diff --git a/app-rust/src/android/transcript_client.rs b/app-rust/src/android/transcript_client.rs
index f08ed15..b866545 100644
--- a/app-rust/src/android/transcript_client.rs
+++ b/app-rust/src/android/transcript_client.rs
@@ -1,11 +1,19 @@
 use crate::client::api::{ApiClient, UreqTransport};
 use crate::client::event_stream::{StreamItem, follow_session_events};
-use crate::client::transcript_fold::{TranscriptItem, fold_event, fold_page, group_tool_runs};
+use crate::client::transcript_fold::{
+    TranscriptItem, fold_event, fold_page, group_tool_runs, raw_seq,
+};
+use crate::ui::{self, TranscriptScreen};
 use event_model::SeqEvent;
 use iris::android::{AndroidAppState, AndroidRsc, AndroidUiState, HasAndroidUiState};
 use iris::prelude::*;
-use std::sync::Arc;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::{
+    sync::{
+        Arc,
+        atomic::{AtomicU64, Ordering},
+    },
+    thread,
+};
 
 pub struct TranscriptClient {
     ui_state: AndroidUiState,
@@ -15,7 +23,7 @@ pub struct TranscriptClient {
     /// `set` calls the way `desktop-app`'s `transcript_ptr` isn't touched
     /// by rebuilding the session list beside it.
     content: WeakWidget<WidgetPtr>,
-    screen: Option<crate::ui::TranscriptScreen>,
+    screen: Option<TranscriptScreen>,
     items: Vec<TranscriptItem>,
     session_id: Option<String>,
     generation: Arc<AtomicU64>,
@@ -189,7 +197,7 @@ impl TranscriptClient {
                 .as_ref()
                 .ok()
                 .and_then(|values| values.last())
-                .and_then(crate::client::transcript_fold::raw_seq)
+                .and_then(raw_seq)
                 .unwrap_or(0);
             let result = page.and_then(|values| fold_page(&values));
 
@@ -251,7 +259,7 @@ impl TranscriptClient {
             .filter(|t| !t.is_empty());
 
         let rows = group_tool_runs(&self.items);
-        let (screen, tree) = crate::ui::build_tree(rsc, rows);
+        let (screen, tree) = ui::build_tree(rsc, rows);
 
         if let Some(text) = in_progress {
             screen.composer.field.edit(rsc).set(&text);
@@ -274,14 +282,14 @@ impl TranscriptClient {
     fn apply_event(&mut self, rsc: &mut AndroidRsc<Self>, event: &SeqEvent) {
         let old_items = self.items.clone();
         self.items = fold_event(&self.items, event);
-        match &self.screen {
+        match self.screen.as_mut() {
             Some(screen) => screen.apply(rsc, &old_items, &self.items),
             None => self.rebuild_transcript(rsc),
         }
     }
 
     fn send_message(&mut self, session_id: String, text: String) {
-        std::thread::spawn(move || {
+        thread::spawn(move || {
             if let Ok(transport) = build_transport() {
                 let api = ApiClient::new(transport);
                 let _ = api.send_message(&session_id, &text, &[]);
diff --git a/app-rust/src/client/transcript_cache.rs b/app-rust/src/client/transcript_cache.rs
index ed0ee06..d876301 100644
--- a/app-rust/src/client/transcript_cache.rs
+++ b/app-rust/src/client/transcript_cache.rs
@@ -1,8 +1,9 @@
-use std::collections::VecDeque;
+use std::collections::{HashSet, VecDeque};
 use std::fs;
 use std::io;
 use std::path::{Path, PathBuf};
-use std::sync::Mutex;
+use std::sync::{Arc, Mutex};
+use std::time::{SystemTime, UNIX_EPOCH};
 
 pub const CACHE_BUDGET_BYTES: u64 = 256_000_000;
 
@@ -14,7 +15,7 @@ pub struct CachedTail {
 
 pub struct TranscriptCache {
     root: PathBuf,
-    warn: std::sync::Arc<dyn Fn(&str) + Send + Sync>,
+    warn: Arc<dyn Fn(&str) + Send + Sync>,
 }
 
 impl TranscriptCache {
@@ -28,7 +29,7 @@ impl TranscriptCache {
     ) -> Self {
         Self {
             root: root.into(),
-            warn: std::sync::Arc::new(warn),
+            warn: Arc::new(warn),
         }
     }
 
@@ -40,7 +41,7 @@ impl TranscriptCache {
     /// successful list fetch. The path out for a session deleted on
     /// another device: nothing here would otherwise hear about it, and
     /// unlike a draft's few bytes what it leaves behind is megabytes.
-    pub fn retain_only(&self, ids: &std::collections::HashSet<String>) {
+    pub fn retain_only(&self, ids: &HashSet<String>) {
         guard_io((), self.warn.as_ref(), || {
             for dir in session_dirs(&self.root)? {
                 if let Some(name) = dir.file_name().and_then(|n| n.to_str())
@@ -61,12 +62,12 @@ impl TranscriptCache {
     /// for.
     pub fn evict_to_budget(&self, keep: &str, budget: u64) {
         guard_io((), self.warn.as_ref(), || {
-            let mut dirs: Vec<(PathBuf, std::time::SystemTime)> = session_dirs(&self.root)?
+            let mut dirs: Vec<(PathBuf, SystemTime)> = session_dirs(&self.root)?
                 .into_iter()
                 .map(|d| {
                     let modified = fs::metadata(&d)
                         .and_then(|m| m.modified())
-                        .unwrap_or(std::time::UNIX_EPOCH);
+                        .unwrap_or(UNIX_EPOCH);
                     (d, modified)
                 })
                 .collect();
@@ -132,7 +133,7 @@ fn dir_size(path: &Path) -> u64 {
 /// closed by paging back through it, but nothing is served across one.
 pub struct SessionCache {
     dir: PathBuf,
-    warn: std::sync::Arc<dyn Fn(&str) + Send + Sync>,
+    warn: Arc<dyn Fn(&str) + Send + Sync>,
     state: Mutex<WriterState>,
 }
 
@@ -145,7 +146,7 @@ struct WriterState {
 }
 
 impl SessionCache {
-    fn new(dir: PathBuf, warn: std::sync::Arc<dyn Fn(&str) + Send + Sync>) -> Self {
+    fn new(dir: PathBuf, warn: Arc<dyn Fn(&str) + Send + Sync>) -> Self {
         Self {
             dir,
             warn,
@@ -333,7 +334,7 @@ impl SessionCache {
     pub fn touch(&self) {
         self.guard((), |this, _state| {
             if this.dir.is_dir() {
-                let now = std::time::SystemTime::now();
+                let now = SystemTime::now();
                 filetime_set_modified(&this.dir, now)?;
             }
             Ok(())
@@ -708,7 +709,7 @@ fn guard_io<T>(
     }
 }
 
-fn filetime_set_modified(path: &Path, _when: std::time::SystemTime) -> io::Result<()> {
+fn filetime_set_modified(path: &Path, _when: SystemTime) -> io::Result<()> {
     use std::io::Write;
     // Rewriting a marker file's contents (rather than the directory itself,
     // which `std` has no portable "touch" for) bumps the directory's own
@@ -728,18 +729,17 @@ fn filetime_set_modified(path: &Path, _when: std::time::SystemTime) -> io::Resul
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::collections::HashSet;
 
     fn cache(temp: &Path) -> TranscriptCache {
-        let said: std::sync::Arc<Mutex<Vec<String>>> = Default::default();
+        let said: Arc<Mutex<Vec<String>>> = Default::default();
         let said2 = said.clone();
         TranscriptCache::with_warn(temp.join("v1/host_8443"), move |msg| {
             said2.lock().unwrap().push(msg.to_string());
         })
     }
 
-    fn cache_with_log(temp: &Path) -> (TranscriptCache, std::sync::Arc<Mutex<Vec<String>>>) {
-        let said: std::sync::Arc<Mutex<Vec<String>>> = Default::default();
+    fn cache_with_log(temp: &Path) -> (TranscriptCache, Arc<Mutex<Vec<String>>>) {
+        let said: Arc<Mutex<Vec<String>>> = Default::default();
         let said2 = said.clone();
         (
             TranscriptCache::with_warn(temp.join("v1/host_8443"), move |msg| {
diff --git a/app-rust/src/client/transcript_fold.rs b/app-rust/src/client/transcript_fold.rs
index dce5beb..36139b7 100644
--- a/app-rust/src/client/transcript_fold.rs
+++ b/app-rust/src/client/transcript_fold.rs
@@ -1,4 +1,5 @@
 use event_model::{Event, QuestionOption, SeqEvent, SessionStatus};
+use std::collections::{HashMap, HashSet};
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct QuestionCard {
@@ -260,11 +261,11 @@ fn split_run(tail: &[TranscriptItem], behind: Option<&str>) -> Vec<TranscriptIte
 /// round that loses nothing.
 pub fn join_pages(earlier: &[TranscriptItem], later: &[TranscriptItem]) -> Vec<TranscriptItem> {
     let (older, newer) = heal_split_message(earlier, later);
-    let started_earlier: std::collections::HashSet<&str> = older
+    let started_earlier: HashSet<&str> = older
         .iter()
         .filter_map(TranscriptItem::as_tool_run)
         .collect();
-    let ended_later: std::collections::HashMap<String, TranscriptItem> = newer
+    let ended_later: HashMap<String, TranscriptItem> = newer
         .iter()
         .filter_map(|item| item.as_tool_run().map(|id| (id.to_string(), item.clone())))
         .filter(|(id, _)| started_earlier.contains(id.as_str()))
diff --git a/app-rust/src/desktop/app.rs b/app-rust/src/desktop/app.rs
index dff267e..018df05 100644
--- a/app-rust/src/desktop/app.rs
+++ b/app-rust/src/desktop/app.rs
@@ -5,8 +5,14 @@ use crate::client::transcript_fold::{
 };
 use event_model::SeqEvent;
 use iris::prelude::*;
-use std::sync::Arc;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::{
+    process,
+    sync::{
+        Arc,
+        atomic::{AtomicU64, Ordering},
+    },
+    thread,
+};
 
 const LIST_WIDTH: f32 = 260.0;
 
@@ -31,12 +37,12 @@ enum AppEvent {
 }
 
 pub fn run() {
-    DefaultApp::<Client>::run();
+    DesktopApp::<Client>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 struct Client {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
     api: Arc<ApiClient<UreqTransport>>,
     stream_transport: Arc<UreqTransport>,
     proxy: Proxy<AppEvent>,
@@ -49,17 +55,17 @@ struct Client {
     generation: Arc<AtomicU64>,
 }
 
-impl DefaultAppState for Client {
+impl DesktopAppState for Client {
     type Event = AppEvent;
 
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         proxy: Proxy<AppEvent>,
     ) -> Self {
         let (server, ca_pem) = super::startup::load_startup_config().unwrap_or_else(|e| {
             eprintln!("desktop-app: {e}");
-            std::process::exit(2);
+            process::exit(2);
         });
         let build_transport =
             || UreqTransport::new(server.base_url(), server.token.clone(), &ca_pem);
@@ -70,7 +76,7 @@ impl DefaultAppState for Client {
                     "desktop-app: couldn't set up TLS to {}: {e}",
                     server.base_url()
                 );
-                std::process::exit(1);
+                process::exit(1);
             });
         let api = Arc::new(ApiClient::new(rest_transport));
         let stream_transport = Arc::new(stream_transport);
@@ -101,7 +107,7 @@ impl DefaultAppState for Client {
         client
     }
 
-    fn event(&mut self, event: AppEvent, rsc: &mut DefaultRsc<Self>) {
+    fn event(&mut self, event: AppEvent, rsc: &mut DesktopRsc<Self>) {
         match event {
             AppEvent::Sessions(Ok(sessions)) => {
                 self.sessions = sessions;
@@ -141,7 +147,7 @@ impl DefaultAppState for Client {
                 if self.current(&session_id, generation) {
                     let old_items = self.items.clone();
                     self.items = fold_event(&self.items, &event);
-                    match &self.screen {
+                    match self.screen.as_mut() {
                         Some(screen) => screen.apply(rsc, &old_items, &self.items),
                         None => self.rebuild_transcript(rsc),
                     }
@@ -171,7 +177,7 @@ impl Client {
             && self.generation.load(Ordering::SeqCst) == generation
     }
 
-    fn show_message(&mut self, rsc: &mut DefaultRsc<Self>, message: &str) {
+    fn show_message(&mut self, rsc: &mut DesktopRsc<Self>, message: &str) {
         let widget = placeholder(rsc, message);
         (self.transcript_ptr)(rsc).set(widget);
     }
@@ -179,13 +185,13 @@ impl Client {
     fn spawn_fetch_sessions(&self) {
         let api = self.api.clone();
         let proxy = self.proxy.clone();
-        std::thread::spawn(move || {
+        thread::spawn(move || {
             let result = api.fetch_sessions().map_err(|e| e.to_string());
             let _ = proxy.send_event(AppEvent::Sessions(result));
         });
     }
 
-    fn rebuild_list(&mut self, rsc: &mut DefaultRsc<Self>) {
+    fn rebuild_list(&mut self, rsc: &mut DesktopRsc<Self>) {
         let list = Span::empty(Dir::DOWN).gap(2).add(rsc);
         for session in &self.sessions {
             let selected = self.selected.as_deref() == Some(session.id.as_str());
@@ -199,7 +205,7 @@ impl Client {
         (self.list_ptr)(rsc).set(tree);
     }
 
-    fn select_session(&mut self, rsc: &mut DefaultRsc<Self>, session_id: String) {
+    fn select_session(&mut self, rsc: &mut DesktopRsc<Self>, session_id: String) {
         let generation = self.generation.fetch_add(1, Ordering::SeqCst) + 1;
         self.selected = Some(session_id.clone());
         self.items.clear();
@@ -211,7 +217,7 @@ impl Client {
         let stream_transport = self.stream_transport.clone();
         let proxy = self.proxy.clone();
         let live_generation = self.generation.clone();
-        std::thread::spawn(move || {
+        thread::spawn(move || {
             let page: Result<Vec<serde_json::Value>, String> = api
                 .fetch_transcript_page(&session_id, None, 200, true)
                 .map_err(|e| e.to_string());
@@ -257,14 +263,14 @@ impl Client {
     fn send_message(&mut self, session_id: String, text: String) {
         let api = self.api.clone();
         let proxy = self.proxy.clone();
-        std::thread::spawn(move || {
+        thread::spawn(move || {
             if let Err(e) = api.send_message(&session_id, &text, &[]) {
                 let _ = proxy.send_event(AppEvent::SendFailed(e.to_string()));
             }
         });
     }
 
-    fn rebuild_transcript(&mut self, rsc: &mut DefaultRsc<Self>) {
+    fn rebuild_transcript(&mut self, rsc: &mut DesktopRsc<Self>) {
         let in_progress = self
             .screen
             .as_ref()
@@ -294,7 +300,7 @@ impl Client {
 }
 
 fn session_row(
-    rsc: &mut DefaultRsc<Client>,
+    rsc: &mut DesktopRsc<Client>,
     session: &SessionSummary,
     selected: bool,
 ) -> StrongWidget {
@@ -313,7 +319,7 @@ fn session_row(
         .background(rect(bg))
         .on(
             CursorSense::click(),
-            move |ctx, rsc: &mut DefaultRsc<Client>| {
+            move |ctx, rsc: &mut DesktopRsc<Client>| {
                 ctx.state.select_session(rsc, id.clone());
             },
         )
@@ -321,7 +327,7 @@ fn session_row(
         .any()
 }
 
-fn placeholder(rsc: &mut DefaultRsc<Client>, message: &str) -> StrongWidget {
+fn placeholder(rsc: &mut DesktopRsc<Client>, message: &str) -> StrongWidget {
     wtext(message.to_string())
         .color(PaintId::WHITE)
         .wrap(true)
diff --git a/app-rust/src/desktop/startup.rs b/app-rust/src/desktop/startup.rs
index 4aae33c..e679f21 100644
--- a/app-rust/src/desktop/startup.rs
+++ b/app-rust/src/desktop/startup.rs
@@ -4,25 +4,22 @@
 //! callers are in the library; the binary is only `fn main`.
 
 use crate::client::config::EnrolledServer;
+use std::{env, fs, path::PathBuf};
 
 use super::config;
 
 struct Args {
-    ca_path: Option<std::path::PathBuf>,
+    ca_path: Option<PathBuf>,
     link: Option<String>,
 }
 
 fn parse_args() -> Result<Args, String> {
     let mut ca_path = None;
     let mut link = None;
-    let mut args = std::env::args().skip(1);
+    let mut args = env::args().skip(1);
     while let Some(arg) = args.next() {
         match arg.as_str() {
-            "--ca" => {
-                ca_path = Some(std::path::PathBuf::from(
-                    args.next().ok_or("--ca needs a path")?,
-                ))
-            }
+            "--ca" => ca_path = Some(PathBuf::from(args.next().ok_or("--ca needs a path")?)),
             "--link" => link = Some(args.next().ok_or("--link needs a value")?),
             other => return Err(format!("unrecognised argument '{other}'")),
         }
@@ -56,7 +53,7 @@ pub fn load_startup_config() -> Result<(EnrolledServer, Vec<u8>), String> {
     // server at a certificate it did not carry -- and so the flag still
     // means what it did before the link could carry one.
     let ca_pem = match (&args.ca_path, &server.ca_pem) {
-        (Some(path), _) => std::fs::read(path)
+        (Some(path), _) => fs::read(path)
             .map_err(|e| format!("couldn't read the CA at {}: {e}", path.display()))?,
         (None, Some(pem)) => pem.clone().into_bytes(),
         (None, None) => {
diff --git a/app-rust/src/ui/mod.rs b/app-rust/src/ui/mod.rs
index 3584a8f..c5c1700 100644
--- a/app-rust/src/ui/mod.rs
+++ b/app-rust/src/ui/mod.rs
@@ -1,8 +1,5 @@
 pub mod composer;
-// The checked-in bench fixture opened as a real screen -- 1.9 MB of
-// `include_str!`, so it is a feature rather than always present: a build
-// meant for a phone must not carry it. `bench` turns it on; so does the
-// default, which is what makes `cargo test` here run the harness tests.
+// Keep the 1.9 MB fixture out of ordinary APKs.
 #[cfg(feature = "fixture")]
 pub mod fixture;
 pub mod markdown;
@@ -11,9 +8,9 @@ pub(crate) mod tap;
 pub mod theme;
 pub mod tool;
 
-use crate::client::transcript_fold::TranscriptRow as FoldedRow;
+use crate::client::transcript_fold::{TranscriptItem, TranscriptRow as FoldedRow, group_tool_runs};
 use iris::prelude::*;
-use std::{cell::RefCell, rc::Rc};
+use std::{mem, rc::Rc};
 use theme::Theme;
 
 pub struct TranscriptScreen {
@@ -25,9 +22,9 @@ pub struct TranscriptScreen {
     /// `.jump_to_end()` directly.
     pub list: WeakWidget<LazySpan>,
     pub composer: composer::Composer,
-    rebuilds: std::cell::Cell<usize>,
-    tail: RefCell<Option<(RowKey, row::TailRow)>>,
-    session_working: std::cell::Cell<bool>,
+    rebuilds: usize,
+    tail: Option<(RowKey, row::TailRow)>,
+    session_working: bool,
     theme: Rc<Theme>,
 }
 
@@ -36,7 +33,7 @@ impl TranscriptScreen {
     /// what a caller's SSE loop or a sent message calls as new events
     /// arrive. `LazySpan::push_back` is O(1) and keeps the view pinned to the
     /// newest content when it already was (I3).
-    pub fn push_row<Rsc: HasEvents>(&self, rsc: &mut Rsc, row: &FoldedRow)
+    pub fn push_row<Rsc: HasEvents>(&mut self, rsc: &mut Rsc, row: &FoldedRow)
     where
         Rsc::State: FocusHost + OpenUrl,
     {
@@ -45,27 +42,27 @@ impl TranscriptScreen {
         // grows through `RowBlocks::apply_delta`, which appends to what is
         // already drawn -- so the cap only ever catches a row that arrived
         // long, which is the one nobody is watching arrive.
-        let (key, widget, tail) = row::build_row(
+        let row::BuiltRow { key, widget, tail } = row::build_row(
             rsc,
             self.list,
             row,
-            self.session_working.get(),
+            self.session_working,
             true,
             self.theme.clone(),
         );
         (self.list)(rsc).push_back(LazyItem::new(key, widget));
-        *self.tail.borrow_mut() = tail.map(|t| (key, t));
+        self.tail = tail.map(|t| (key, t));
     }
 
-    pub fn set_session_working<Rsc: HasEvents>(&self, rsc: &mut Rsc, working: bool)
+    pub fn set_session_working<Rsc: HasEvents>(&mut self, rsc: &mut Rsc, working: bool)
     where
         Rsc::State: FocusHost + OpenUrl,
     {
-        if self.session_working.replace(working) == working {
+        if self.session_working == working {
             return;
         }
-        let mut tail = self.tail.borrow_mut();
-        if let Some((_, row::TailRow::Tools(tools))) = tail.as_mut() {
+        self.session_working = working;
+        if let Some((_, row::TailRow::Tools(tools))) = self.tail.as_mut() {
             let calls = tools.calls();
             tools.apply_calls(rsc, &calls, working);
         }
@@ -73,7 +70,7 @@ impl TranscriptScreen {
 
     #[cfg(test)]
     fn tail_card_count(&self) -> usize {
-        match self.tail.borrow().as_ref() {
+        match self.tail.as_ref() {
             Some((_, row::TailRow::Tools(tools))) => tools.card_count(),
             _ => 0,
         }
@@ -84,12 +81,11 @@ impl TranscriptScreen {
     /// displayless machine, and the tests below). Answers whether there
     /// was such a row to act on, so a caller that expected one can say so
     /// rather than silently producing the collapsed picture.
-    pub fn expand_tail_tools<Rsc: HasEvents>(&self, rsc: &mut Rsc, expanded: bool) -> bool
+    pub fn expand_tail_tools<Rsc: HasEvents>(&mut self, rsc: &mut Rsc, expanded: bool) -> bool
     where
         Rsc::State: FocusHost + OpenUrl,
     {
-        let tail = self.tail.borrow();
-        let Some((_, row::TailRow::Tools(tools))) = tail.as_ref() else {
+        let Some((_, row::TailRow::Tools(tools))) = self.tail.as_ref() else {
             return false;
         };
         tools.set_group_expanded(rsc, expanded);
@@ -99,12 +95,16 @@ impl TranscriptScreen {
     /// The `ReplaceLast` fast path: update the tail row in place if this
     /// really is a change to the same row, and say whether that worked.
     /// `false` for anything the caller must rebuild instead.
-    fn apply_tail_delta<Rsc: HasEvents>(&self, rsc: &mut Rsc, key: RowKey, row: &FoldedRow) -> bool
+    fn apply_tail_delta<Rsc: HasEvents>(
+        &mut self,
+        rsc: &mut Rsc,
+        key: RowKey,
+        row: &FoldedRow,
+    ) -> bool
     where
         Rsc::State: FocusHost + OpenUrl,
     {
-        let mut tail = self.tail.borrow_mut();
-        let Some((tail_key, kept)) = tail.as_mut() else {
+        let Some((tail_key, kept)) = self.tail.as_mut() else {
             return false;
         };
         if *tail_key != key {
@@ -116,19 +116,16 @@ impl TranscriptScreen {
                 // A tool call is drawn as a card, never as markdown, so a
                 // row that kept blocks and now holds one is a different
                 // row -- rebuild it.
-                if matches!(
-                    item,
-                    crate::client::transcript_fold::TranscriptItem::ToolRun { .. }
-                ) {
+                if matches!(item, TranscriptItem::ToolRun { .. }) {
                     return false;
                 }
                 blocks.apply_delta(rsc, sender, &markdown_src)
             }
             (row::TailRow::Tools(tools), FoldedRow::Tools(calls)) => {
-                tools.apply_calls(rsc, calls, self.session_working.get())
+                tools.apply_calls(rsc, calls, self.session_working)
             }
             (row::TailRow::Tools(tools), FoldedRow::Single(item)) => {
-                tools.apply_calls(rsc, std::slice::from_ref(item), self.session_working.get())
+                tools.apply_calls(rsc, std::slice::from_ref(item), self.session_working)
             }
             (row::TailRow::Blocks(_), FoldedRow::Tools(_)) => false,
         }
@@ -143,15 +140,13 @@ impl TranscriptScreen {
     /// often the fallback actually fires rather than assuming it never
     /// does.
     pub fn apply<Rsc: HasEvents>(
-        &self,
+        &mut self,
         rsc: &mut Rsc,
-        old: &[crate::client::transcript_fold::TranscriptItem],
-        new: &[crate::client::transcript_fold::TranscriptItem],
+        old: &[TranscriptItem],
+        new: &[TranscriptItem],
     ) where
         Rsc::State: FocusHost + OpenUrl,
     {
-        use crate::client::transcript_fold::group_tool_runs;
-
         let old_rows = group_tool_runs(old);
         let new_rows = group_tool_runs(new);
 
@@ -172,25 +167,29 @@ impl TranscriptScreen {
                     return;
                 }
 
-                let (new_key, widget, kept) = row::build_row(
+                let row::BuiltRow {
+                    key: new_key,
+                    widget,
+                    tail: kept,
+                } = row::build_row(
                     rsc,
                     self.list,
                     &new_rows[common],
-                    self.session_working.get(),
+                    self.session_working,
                     false,
                     self.theme.clone(),
                 );
                 let evicted = (self.list)(rsc).replace_back(LazyItem::new(new_key, widget));
                 drop(evicted); // frees the old row's widget, same as a pop would
-                *self.tail.borrow_mut() = kept.map(|t| (new_key, t));
+                self.tail = kept.map(|t| (new_key, t));
                 for row in &new_rows[common + 1..] {
                     self.push_row(rsc, row);
                 }
             }
             RowDiff::Rebuild => {
-                self.rebuilds.set(self.rebuilds.get() + 1);
+                self.rebuilds += 1;
                 (self.list)(rsc).clear();
-                *self.tail.borrow_mut() = None;
+                self.tail = None;
                 for row in &new_rows {
                     self.push_row(rsc, row);
                 }
@@ -198,8 +197,8 @@ impl TranscriptScreen {
         }
     }
 
-    pub fn take_rebuilds(&self) -> usize {
-        self.rebuilds.replace(0)
+    pub fn take_rebuilds(&mut self) -> usize {
+        mem::take(&mut self.rebuilds)
     }
 
     /// The semantic paint IDs used by this screen. A caller can replace
@@ -268,7 +267,11 @@ where
         // be a reply already streaming when this screen opened, and a
         // capped row cannot take a delta (`RowBlocks::capped`).
         let cap = i + 1 < rows.len();
-        let (key, widget, kept) = row::build_row(rsc, list, row, false, cap, theme.clone());
+        let row::BuiltRow {
+            key,
+            widget,
+            tail: kept,
+        } = row::build_row(rsc, list, row, false, cap, theme.clone());
         list(rsc).push_back(LazyItem::new(key, widget));
         tail = kept.map(|t| (key, t));
     }
@@ -303,11 +306,11 @@ where
 
     (
         TranscriptScreen {
-            tail: RefCell::new(tail),
-            session_working: std::cell::Cell::new(false),
+            tail,
+            session_working: false,
             list,
             composer,
-            rebuilds: std::cell::Cell::new(0),
+            rebuilds: 0,
             theme,
         },
         tree,
@@ -348,7 +351,6 @@ fn diff_rows(old: &[FoldedRow], new: &[FoldedRow]) -> RowDiff {
 #[cfg(test)]
 mod diff_tests {
     use super::*;
-    use crate::client::transcript_fold::TranscriptItem;
 
     fn user(seq: u64, text: &str) -> FoldedRow {
         FoldedRow::Single(TranscriptItem::UserMsg {
@@ -433,7 +435,8 @@ mod diff_tests {
 #[cfg(test)]
 mod apply_tests {
     use super::*;
-    use crate::client::transcript_fold::TranscriptItem;
+    use crate::client::text_cap::MESSAGE_LINES;
+    use std::iter;
 
     struct TestFocus {
         focus: Option<WeakWidget<TextEdit>>,
@@ -523,10 +526,7 @@ mod apply_tests {
             1,
             &reply(paragraphs, "and the last one is still going."),
         )];
-        let (screen, tree) = build_tree(
-            &mut rsc,
-            crate::client::transcript_fold::group_tool_runs(&old_items),
-        );
+        let (mut screen, tree) = build_tree(&mut rsc, group_tool_runs(&old_items));
         let mut render = UiRenderState::new();
         render.resize((1080.0, 20000.0));
         render.update(&tree, &mut rsc);
@@ -535,7 +535,7 @@ mod apply_tests {
         screen.apply(&mut rsc, &old_items, &new_items);
         render.update(&tree, &mut rsc);
         assert_eq!(screen.take_rebuilds(), 0, "the delta path must be taken");
-        let (draws, _, _, shapes) = render.take_counters();
+        let RenderCounters { draws, shapes, .. } = render.take_counters();
         (draws, shapes)
     }
 
@@ -585,8 +585,7 @@ mod apply_tests {
         rsc: &mut TestRsc,
         items: &[TranscriptItem],
     ) -> (TranscriptScreen, StrongWidget, UiRenderState) {
-        let (screen, tree) =
-            build_tree(rsc, crate::client::transcript_fold::group_tool_runs(items));
+        let (mut screen, tree) = build_tree(rsc, group_tool_runs(items));
         let mut render = UiRenderState::new();
         render.resize((1080.0, 20000.0));
         render.update(&tree, rsc);
@@ -605,10 +604,7 @@ mod apply_tests {
             events: EventManager::default(),
         };
         let items = run_of(3, output, true);
-        let (screen, tree) = build_tree(
-            &mut rsc,
-            crate::client::transcript_fold::group_tool_runs(&items),
-        );
+        let (mut screen, tree) = build_tree(&mut rsc, group_tool_runs(&items));
         let mut render = UiRenderState::new();
         render.resize((1080.0, 20000.0));
         render.update(&tree, &mut rsc);
@@ -619,13 +615,12 @@ mod apply_tests {
             "the fixture's only row must be the tool run"
         );
         render.update(&tree, &mut rsc);
-        let (_, _, _, shapes) = render.take_counters();
-        shapes
+        render.take_counters().shapes
     }
 
     #[test]
     fn collapsed_cards_shape_only_their_summary_lines() {
-        let long: String = std::iter::repeat_n("a line of tool output\n", 4_000).collect();
+        let long: String = iter::repeat_n("a line of tool output\n", 4_000).collect();
         assert!(long.len() > 80_000, "the long case must actually be long");
 
         let short_shapes = shapes_to_open("ok\n");
@@ -659,22 +654,18 @@ mod apply_tests {
                 settled: true,
             },
         ];
-        let (_screen, tree) = build_tree(
-            &mut rsc,
-            crate::client::transcript_fold::group_tool_runs(&items),
-        );
+        let (_screen, tree) = build_tree(&mut rsc, group_tool_runs(&items));
         let mut render = UiRenderState::new();
         render.resize((1080.0, 20000.0));
         render.update(&tree, &mut rsc);
-        let (_, _, _, shapes) = render.take_counters();
-        shapes
+        render.take_counters().shapes
     }
 
     #[test]
     fn a_long_message_is_drawn_only_as_far_as_the_cap() {
         let paragraphs = |n: usize| "a paragraph of a reply\n\n".repeat(n);
-        let capped = shapes_for_message(&paragraphs(crate::client::text_cap::MESSAGE_LINES * 4));
-        let bigger = shapes_for_message(&paragraphs(crate::client::text_cap::MESSAGE_LINES * 40));
+        let capped = shapes_for_message(&paragraphs(MESSAGE_LINES * 4));
+        let bigger = shapes_for_message(&paragraphs(MESSAGE_LINES * 40));
         assert!(
             capped > 0,
             "the screen shaped nothing, so this compares zeroes"
@@ -695,7 +686,7 @@ mod apply_tests {
         let mut after = before.clone();
         after[0] = call("t0", "the result", true);
 
-        let (screen, tree, mut render) = open_run(&mut rsc, &before);
+        let (mut screen, tree, mut render) = open_run(&mut rsc, &before);
         screen.apply(&mut rsc, &before, &after);
         render.update(&tree, &mut rsc);
         assert_eq!(
@@ -703,8 +694,7 @@ mod apply_tests {
             0,
             "a result arriving must not rebuild the whole screen"
         );
-        let (draws, _, _, _) = render.take_counters();
-        draws
+        render.take_counters().draws
     }
 
     #[test]
@@ -732,10 +722,7 @@ mod apply_tests {
         let mut after = before.clone();
         after[1] = call("t1", "done", true);
 
-        let (screen, tree) = build_tree(
-            &mut rsc,
-            crate::client::transcript_fold::group_tool_runs(&before),
-        );
+        let (mut screen, tree) = build_tree(&mut rsc, group_tool_runs(&before));
         let mut render = UiRenderState::new();
         render.resize((1080.0, 20000.0));
         render.update(&tree, &mut rsc);
@@ -767,7 +754,7 @@ mod apply_tests {
         let mut after = before.clone();
         after.push(call("t2", "", false));
 
-        let (screen, tree, mut render) = open_run(&mut rsc, &before);
+        let (mut screen, tree, mut render) = open_run(&mut rsc, &before);
         assert_eq!(screen.tail_card_count(), 2);
         screen.apply(&mut rsc, &before, &after);
         render.update(&tree, &mut rsc);
@@ -787,10 +774,7 @@ mod apply_tests {
         };
         let before = vec![user(1, "stable"), call("t0", "", false)];
         let after = vec![user(1, "stable"), user(2, "not a tool call at all")];
-        let (screen, _tree) = build_tree(
-            &mut rsc,
-            crate::client::transcript_fold::group_tool_runs(&before),
-        );
+        let (mut screen, _tree) = build_tree(&mut rsc, group_tool_runs(&before));
         screen.apply(&mut rsc, &before, &after);
         assert_eq!(
             screen.take_rebuilds(),
diff --git a/app-rust/src/ui/row.rs b/app-rust/src/ui/row.rs
index 67906a8..4d8aa8f 100644
--- a/app-rust/src/ui/row.rs
+++ b/app-rust/src/ui/row.rs
@@ -1,32 +1,31 @@
 use crate::client::markdown_blocks::{Block, BlockKind, common_prefix, split_blocks};
 use crate::client::text_cap::{MESSAGE_BYTES, MESSAGE_LINES, cut, show_all_label};
-use crate::client::transcript_fold::{QuestionCard, TranscriptItem, TranscriptRow as FoldedRow};
+use crate::client::transcript_fold::{
+    ItemKey, QuestionCard, TranscriptItem, TranscriptRow as FoldedRow,
+};
 use crate::ui::markdown::{BlockFrame, Link, frame_of, render_block};
 use crate::ui::tap::{hold_edge, on_tap};
 use crate::ui::theme::Theme;
-use crate::ui::tool::ToolRow;
+use crate::ui::tool::{ToolRow, build_tool_row};
 use iris::prelude::*;
-use std::{cell::RefCell, rc::Rc};
+use std::{
+    cell::RefCell,
+    collections::hash_map::DefaultHasher,
+    hash::{Hash, Hasher},
+    rc::Rc,
+    slice,
+};
 
 const BLOCK_GAP_DP: f32 = 8.0;
 
 pub const BASE_SIZE: f32 = 16.0;
 
-/// `ItemKey::Seq` already is the `RowKey` (`u64`) this crate's `LazySpan` wants.
-/// `ItemKey::RunId` is a string (a tool call's own id), so it is hashed into
-/// one -- collisions are not a correctness risk worth guarding against here
-/// (a `DefaultHasher` collision across the run ids one session produces is
-/// astronomically unlikely, and the consequence of one would only be two
-/// tool-call rows sharing a list slot, not data loss), and the high bit is
-/// forced on so a hashed key can never collide with a real sequence number
-/// (this build never produces 2^63 events).
-pub fn row_key(key: &crate::client::transcript_fold::ItemKey) -> RowKey {
-    use crate::client::transcript_fold::ItemKey;
-    use std::hash::{Hash, Hasher};
+/// Maps string run IDs above the sequence-number range used by transcripts.
+pub fn row_key(key: &ItemKey) -> RowKey {
     match key {
         ItemKey::Seq(seq) => *seq,
         ItemKey::RunId(id) => {
-            let mut h = std::collections::hash_map::DefaultHasher::new();
+            let mut h = DefaultHasher::new();
             id.hash(&mut h);
             h.finish() | (1 << 63)
         }
@@ -94,19 +93,10 @@ fn tool_call_markdown(tool: &str, input: &str, output: &str) -> String {
 pub struct RowBlocks {
     blocks: Vec<Block>,
     fields: Vec<WeakWidget<Text>>,
-    links: Vec<Rc<RefCell<Vec<Link>>>>,
+    links: Vec<LinkTargets>,
     column: WeakWidget<Span>,
     sender: Option<String>,
-    /// Whether this row draws less than the whole message
-    /// ([`cap_message`]). A delta cannot be appended to a capped row --
-    /// the new text would go on *below* the "Show all" that says it is
-    /// hidden -- so [`RowBlocks::apply_delta`] refuses one and the caller
-    /// rebuilds instead.
-    ///
-    /// Never `true` for the row a reply is actually streaming into: the
-    /// live tail is built uncapped ([`build_row`]'s `cap`), which is what
-    /// keeps the refusal from costing anything in practice. This field is
-    /// the belt to that braces.
+    /// A capped row must be rebuilt before accepting a delta.
     capped: bool,
     theme: Rc<Theme>,
 }
@@ -126,17 +116,7 @@ fn display_blocks(markdown_src: &str) -> Vec<Block> {
     }
 }
 
-/// `blocks` cut to what a row draws, with the line count of the **whole**
-/// message; `None` when all of it fits.
-///
-/// The cut prefers a **block boundary**, because a message is markdown and
-/// a whole paragraph is a smaller version of a message in a way that half
-/// a paragraph is not. Where one block is over the bound by itself -- the
-/// reply that is one enormous fence -- that block is truncated instead of
-/// being dropped or drawn whole: dropping it would leave a row saying
-/// nothing, and a truncated fence still renders as a fence, since the
-/// renderer already knows the block's kind and pulldown-cmark closes an
-/// unterminated one at the end of its input.
+/// Caps at a block boundary when possible, or within the first oversized block.
 fn cap_message(blocks: Vec<Block>, cap: bool) -> (Vec<Block>, Option<usize>) {
     let total = || blocks.iter().map(|b| b.source.lines().count()).sum();
     if !cap {
@@ -167,30 +147,50 @@ fn cap_message(blocks: Vec<Block>, cap: bool) -> (Vec<Block>, Option<usize>) {
     (kept, None)
 }
 
-/// A message's own text, kept so that asking for the whole of a capped row
-/// can rebuild it. `Rc` rather than a copy per closure: the source of a
-/// long message is the largest string in the row, and the tap handler
-/// would otherwise hold a second one for the lifetime of the row.
+/// Shared with the "Show all" callback to avoid copying a long message.
 struct RowSource {
     sender: Option<String>,
     markdown: String,
 }
 
+#[derive(Clone)]
+struct LinkTargets(Rc<RefCell<Vec<Link>>>);
+
+impl LinkTargets {
+    fn new(links: Vec<Link>) -> Self {
+        Self(Rc::new(RefCell::new(links)))
+    }
+
+    fn replace(&self, links: Vec<Link>) {
+        *self.0.borrow_mut() = links;
+    }
+
+    fn url_at(&self, byte: usize) -> Option<String> {
+        self.0
+            .borrow()
+            .iter()
+            .find(|link| link.range.contains(&byte))
+            .map(|link| link.url.clone())
+    }
+}
+
+struct BuiltBlock {
+    field: WeakWidget<Text>,
+    widget: StrongWidget,
+    links: LinkTargets,
+}
+
 const FRAME_PAD_DP: f32 = 10.0;
 const QUOTE_BAR_DP: f32 = 3.0;
 const FRAME_RADIUS_DP: f32 = 8.0;
 
-fn build_block<Rsc: HasEvents>(
-    rsc: &mut Rsc,
-    block: &Block,
-    theme: &Theme,
-) -> (WeakWidget<Text>, StrongWidget, Rc<RefCell<Vec<Link>>>)
+fn build_block<Rsc: HasEvents>(rsc: &mut Rsc, block: &Block, theme: &Theme) -> BuiltBlock
 where
     Rsc::State: FocusHost + OpenUrl,
 {
     let frame = frame_of(block.kind, theme);
     let rendered = render_block(block, BASE_SIZE, theme);
-    let links = Rc::new(RefCell::new(rendered.links));
+    let links = LinkTargets::new(rendered.links);
     let verbatim = matches!(frame, BlockFrame::Verbatim { .. });
     let field = wtext(rendered.text)
         .spans(rendered.spans)
@@ -218,17 +218,10 @@ where
                     selection.drag(id, rsc, input)
                 })
                 .unwrap_or(SelectionInput::Tapped);
-            // A *tap*, decided by the same `DragArbiter` the pan and
-            // the selection are: a gesture that panned the list past
-            // this link, or held long enough to select, must not also
-            // follow it (`GestureOutcome::Tapped`'s doc).
+            // Panning or selecting across a link must not open it.
             if outcome == SelectionInput::Tapped {
                 let byte = field.selection(rsc).byte_at(pos, size);
-                let url = tap_links
-                    .borrow()
-                    .iter()
-                    .find(|l| l.range.contains(&byte))
-                    .map(|l| l.url.clone());
+                let url = tap_links.url_at(byte);
                 if let Some(url) = url {
                     log::info!("iris link: opening {url}");
                     <Rsc::State as OpenUrl>::open_url(ctx.state, &url);
@@ -257,7 +250,11 @@ where
             .add_strong(rsc)
             .any(),
     };
-    (field, framed, links)
+    BuiltBlock {
+        field,
+        widget: framed,
+        links,
+    }
 }
 
 #[allow(clippy::too_many_arguments)]
@@ -305,10 +302,10 @@ where
     let mut fields = Vec::with_capacity(blocks.len());
     let mut links = Vec::with_capacity(blocks.len());
     for block in &blocks {
-        let (field, framed, block_links) = build_block(rsc, block, &theme);
-        fields.push(field);
-        links.push(block_links);
-        column.push(framed);
+        let built = build_block(rsc, block, &theme);
+        fields.push(built.field);
+        links.push(built.links);
+        column.push(built.widget);
     }
     if let Some(lines) = hidden {
         column.push(show_all(
@@ -323,14 +320,7 @@ where
     }
     let column = column.add(rsc);
 
-    // `.add` (weak), not `.add_strong` -- `header` is about to be embedded
-    // as a child of the `.span(Dir::DOWN)` below, whose own composition is
-    // what performs the *one* real strong registration each child gets.
-    // Calling `.add_strong`/`.upgrade` here too, then feeding a `.weak()`
-    // copy into that composition, tried to strong-register the same id
-    // twice and panicked with "was already added"
-    // (`core/src/widget/like.rs:12`) -- found running this crate's own
-    // `run-headless.sh` example, the first real render of a row.
+    // The parent composition performs the header's single strong registration.
     let header: WeakWidget = match &source.sender {
         Some(name) => wtext(name.clone())
             .size(13.0)
@@ -359,9 +349,7 @@ where
     )
 }
 
-/// The `RowBlocks` the rebuild produces is **discarded**, because a capped
-/// row is never the row a reply is streaming into (`build_row`'s `cap`) --
-/// so nothing is holding one for it, and there is nothing to keep in step.
+/// Rebuilds a capped row uncapped; its incremental state is intentionally discarded.
 #[allow(clippy::too_many_arguments)]
 fn show_all<Rsc: HasEvents>(
     rsc: &mut Rsc,
@@ -395,12 +383,7 @@ where
 }
 
 impl RowBlocks {
-    /// Bring this row up to date with `markdown_src` **without** re-laying
-    /// out the blocks that did not change, and say whether that was
-    /// possible. `false` means the caller must rebuild the row the
-    /// ordinary way: an earlier block was rewritten (markdown allows it --
-    /// a trailing `---` turns the paragraph above into a heading), the
-    /// sender changed, or the message got shorter.
+    /// Updates only the changed tail blocks, or returns `false` when a rebuild is required.
     pub fn apply_delta<Rsc: HasEvents>(
         &mut self,
         rsc: &mut Rsc,
@@ -413,20 +396,12 @@ impl RowBlocks {
         if self.sender.as_deref() != sender {
             return false;
         }
-        // A capped row draws less than the message it was built from, so
-        // appending to it would put the new text *below* the "Show all"
-        // saying the rest is hidden. The caller rebuilds instead, and
-        // rebuilds uncapped (`TranscriptScreen::apply`), so this refusal
-        // costs one rebuild per message rather than one per delta.
         if self.capped {
             return false;
         }
         let new_blocks = display_blocks(markdown_src);
         let common = common_prefix(&self.blocks, &new_blocks);
-        // Everything already drawn must either be kept whole (`common ==
-        // len`, a pure append) or be kept except for the last block, which
-        // is the one a delta lands in. Anything else means an already
-        // laid-out block is no longer what it was.
+        // A delta may append or rewrite only the current final block.
         if new_blocks.len() < self.blocks.len() || common + 1 < self.blocks.len() {
             return false;
         }
@@ -449,14 +424,14 @@ impl RowBlocks {
                 (Some(field), Some(links)) => {
                     let rendered = render_block(block, BASE_SIZE, &self.theme);
                     field(rsc).set_with_spans(rendered.text, rendered.spans);
-                    *links.borrow_mut() = rendered.links;
+                    links.replace(rendered.links);
                 }
                 _ => {
-                    let (field, framed, links) = build_block(rsc, block, &self.theme);
-                    self.fields.push(field);
-                    self.links.push(links);
+                    let built = build_block(rsc, block, &self.theme);
+                    self.fields.push(built.field);
+                    self.links.push(built.links);
                     if let Some(column) = rsc.ui_mut().widgets.get_mut(&self.column) {
-                        column.push(framed);
+                        column.push(built.widget);
                     }
                 }
             }
@@ -481,20 +456,19 @@ where
     build_text_row(rsc, list, key, sender, &markdown_src, cap, theme)
 }
 
-/// Two mechanisms would have been two answers to the same question ("what
-/// can this row do cheaply?"), so the caller holds one of these for its
-/// tail row and asks it, rather than holding a `RowBlocks` and a
-/// `ToolRow` and choosing between them at each call site.
+/// Incremental state retained for whichever kind of row is currently last.
 pub enum TailRow {
     Blocks(RowBlocks),
     Tools(ToolRow),
 }
 
-/// `cap` draws a long message as [`cap_message`]'s worth of it behind a
-/// "Show all"; the caller passes `false` for the **live tail**, the row a
-/// reply is streaming into, because a row that grows while it is capped
-/// would appear to stop growing (`RowBlocks::capped`). Every other row is
-/// capped.
+pub struct BuiltRow {
+    pub key: RowKey,
+    pub widget: StrongWidget,
+    pub tail: Option<TailRow>,
+}
+
+/// `cap` limits historical rows; a live tail must remain uncapped.
 pub fn build_row<Rsc: HasEvents>(
     rsc: &mut Rsc,
     list: WeakWidget<LazySpan>,
@@ -502,33 +476,35 @@ pub fn build_row<Rsc: HasEvents>(
     working: bool,
     cap: bool,
     theme: Rc<Theme>,
-) -> (RowKey, StrongWidget, Option<TailRow>)
+) -> BuiltRow
 where
     Rsc::State: FocusHost + OpenUrl,
 {
-    // A lone tool call is a card too, not a message with markdown in it:
-    // `group_tool_runs` leaves one call as a `Single` because "Called 1
-    // tool" hides a card to say the same thing in more words, and the
-    // *card* is what both cases draw (`ToolRows.kt`).
+    // A single tool call still draws as a card, without a redundant group wrapper.
     let calls = match row {
-        FoldedRow::Single(item @ TranscriptItem::ToolRun { .. }) => {
-            Some(std::slice::from_ref(item))
-        }
+        FoldedRow::Single(item @ TranscriptItem::ToolRun { .. }) => Some(slice::from_ref(item)),
         FoldedRow::Tools(calls) => Some(calls.as_slice()),
         FoldedRow::Single(_) => None,
     };
     if let Some(calls) = calls {
         let key = row_key(&calls[0].key());
-        let (widget, tools) =
-            crate::ui::tool::build_tool_row(rsc, list, key, calls.to_vec(), working, theme);
-        return (key, widget, Some(TailRow::Tools(tools)));
+        let (widget, tools) = build_tool_row(rsc, list, key, calls.to_vec(), working, theme);
+        return BuiltRow {
+            key,
+            widget,
+            tail: Some(TailRow::Tools(tools)),
+        };
     }
     let FoldedRow::Single(item) = row else {
         unreachable!("every Tools row took the branch above");
     };
     let key = row_key(&item.key());
     let (widget, blocks) = build_single(rsc, list, key, item, cap, theme);
-    (key, widget, Some(TailRow::Blocks(blocks)))
+    BuiltRow {
+        key,
+        widget,
+        tail: Some(TailRow::Blocks(blocks)),
+    }
 }
 
 #[cfg(test)]
diff --git a/app-rust/src/ui/tool.rs b/app-rust/src/ui/tool.rs
index e0535ef..4e236a7 100644
--- a/app-rust/src/ui/tool.rs
+++ b/app-rust/src/ui/tool.rs
@@ -5,7 +5,11 @@ use crate::ui::markdown::highlight_into;
 use crate::ui::tap::{hold_edge, on_tap};
 use crate::ui::theme::Theme;
 use iris::prelude::*;
-use std::{cell::Cell, cell::RefCell, collections::HashMap, rc::Rc};
+use std::{
+    cell::{Cell, RefCell},
+    collections::{HashMap, HashSet},
+    rc::Rc,
+};
 
 const NAME_SIZE: f32 = 14.0;
 const BODY_SIZE: f32 = 12.0;
@@ -591,7 +595,7 @@ impl ToolRow {
         let changed: Vec<usize> = (0..old.len()).filter(|&i| old[i] != calls[i]).collect();
         self.shared.working.set(working);
         *self.shared.calls.borrow_mut() = calls.to_vec();
-        let ids: std::collections::HashSet<String> = calls
+        let ids: HashSet<String> = calls
             .iter()
             .filter_map(|c| match c {
                 TranscriptItem::ToolRun { id, .. } => Some(id.clone()),
diff --git a/app-rust/tests/fence_fling.rs b/app-rust/tests/fence_fling.rs
index 41f7e75..650664b 100644
--- a/app-rust/tests/fence_fling.rs
+++ b/app-rust/tests/fence_fling.rs
@@ -49,7 +49,7 @@ fn a_flick_across_a_code_fence_keeps_moving_after_the_finger_leaves() {
 
     let mut h = Harness::new(phone_size(), PHONE_SCALE);
     let opened = ai_app::ui::fixture::open(&mut h.rsc, &mut h.state).expect("the fixture folds");
-    let screen = opened.screen;
+    let mut screen = opened.screen;
     h.frame(0);
     h.frame(PHONE_FRAME_MS);
 
@@ -119,7 +119,7 @@ fn a_drag_away_from_a_coasting_fence_scrolls_the_list_and_leaves_it_coasting() {
 
     let mut h = Harness::new(phone_size(), PHONE_SCALE);
     let opened = ai_app::ui::fixture::open(&mut h.rsc, &mut h.state).expect("the fixture folds");
-    let screen = opened.screen;
+    let mut screen = opened.screen;
     h.frame(0);
     h.frame(PHONE_FRAME_MS);
 
diff --git a/app-rust/tests/gesture_cancel.rs b/app-rust/tests/gesture_cancel.rs
index e896978..92e42cf 100644
--- a/app-rust/tests/gesture_cancel.rs
+++ b/app-rust/tests/gesture_cancel.rs
@@ -87,7 +87,7 @@ fn a_press_ended_by_a_cancel_leaves_no_origin_for_the_next_one() {
 fn panning_a_code_fence_then_tapping_elsewhere_moves_nothing() {
     use ai_app::client::transcript_fold::{TranscriptItem, TranscriptRow};
 
-    let (mut h, screen) = opened();
+    let (mut h, mut screen) = opened();
     let fence = TranscriptRow::Single(TranscriptItem::AssistantMsg {
         seq: 9_000_000,
         text: "```\none two three four five six seven eight nine ten eleven twelve\n\
diff --git a/iris/benches/message_list.rs b/iris/benches/message_list.rs
index b3cff62..5898519 100644
--- a/iris/benches/message_list.rs
+++ b/iris/benches/message_list.rs
@@ -68,7 +68,12 @@ fn bench_first_frame(n: usize) {
     let start = Instant::now();
     render.update(&root, &mut rsc);
     let elapsed = start.elapsed();
-    let (draws, rewrites, moves, _shapes) = render.take_counters();
+    let RenderCounters {
+        draws,
+        region_rewrites: rewrites,
+        moves,
+        ..
+    } = render.take_counters();
     report(
         &format!("(a) first frame, N={n}"),
         elapsed,
@@ -97,7 +102,12 @@ fn bench_scroll(n: usize, ticks: usize) {
         let start = Instant::now();
         render.update(&root, &mut rsc);
         total += start.elapsed();
-        let (draws, rewrites, moves, _shapes) = render.take_counters();
+        let RenderCounters {
+            draws,
+            region_rewrites: rewrites,
+            moves,
+            ..
+        } = render.take_counters();
         total_draws += draws;
         total_rewrites += rewrites;
         total_moves += moves;
@@ -155,7 +165,12 @@ fn bench_input_grows(n: usize, lines: usize) {
         let start = Instant::now();
         render.update(&root, &mut rsc);
         total += start.elapsed();
-        let (draws, rewrites, moves, _shapes) = render.take_counters();
+        let RenderCounters {
+            draws,
+            region_rewrites: rewrites,
+            moves,
+            ..
+        } = render.take_counters();
         total_draws += draws;
         total_rewrites += rewrites;
         total_moves += moves;
@@ -200,7 +215,12 @@ fn bench_insert_above_anchor(n: usize, inserts: usize) {
         let start = Instant::now();
         render.update(&root, &mut rsc);
         total += start.elapsed();
-        let (draws, rewrites, moves, _shapes) = render.take_counters();
+        let RenderCounters {
+            draws,
+            region_rewrites: rewrites,
+            moves,
+            ..
+        } = render.take_counters();
         total_draws += draws;
         total_rewrites += rewrites;
         total_moves += moves;
@@ -270,7 +290,12 @@ fn bench_expand_holds_edge(n: usize, growths: usize) {
         let start = Instant::now();
         render.update(&root, &mut rsc);
         total += start.elapsed();
-        let (draws, rewrites, moves, _shapes) = render.take_counters();
+        let RenderCounters {
+            draws,
+            region_rewrites: rewrites,
+            moves,
+            ..
+        } = render.take_counters();
         total_draws += draws;
         total_rewrites += rewrites;
         total_moves += moves;
@@ -314,7 +339,12 @@ fn bench_redraw_big_text(chars: usize, redraws: usize) {
         render.update(&root, &mut rsc);
         total += start.elapsed();
     }
-    let (draws, rewrites, moves, _shapes) = render.take_counters();
+    let RenderCounters {
+        draws,
+        region_rewrites: rewrites,
+        moves,
+        ..
+    } = render.take_counters();
     report(
         &format!("(g) redraw one {chars}-glyph text, {redraws}x (totals)"),
         total,
diff --git a/iris/core/src/ui/access.rs b/iris/core/src/ui/access.rs
index c742d0e..d8c8306 100644
--- a/iris/core/src/ui/access.rs
+++ b/iris/core/src/ui/access.rs
@@ -32,7 +32,7 @@ fn entry_node(entry: &Entry) -> Node {
 /// Owns the last tree pushed out, so `update` can tell "nothing
 /// accessibility-relevant changed" from "something did" without asking
 /// the platform adapter to diff two `Node`s itself. One of these per
-/// window/view -- `default::DefaultUiState` and `android::AndroidUiState`
+/// window/view -- `desktop::DesktopUiState` and `android::AndroidUiState`
 /// each keep one.
 #[derive(Default)]
 pub struct AccessTree {
diff --git a/iris/core/src/ui/render_state.rs b/iris/core/src/ui/render_state.rs
index 6bb0a53..928b21e 100644
--- a/iris/core/src/ui/render_state.rs
+++ b/iris/core/src/ui/render_state.rs
@@ -18,6 +18,14 @@ pub enum RedrawKind {
     Updates,
 }
 
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct RenderCounters {
+    pub draws: u64,
+    pub region_rewrites: u64,
+    pub moves: u64,
+    pub shapes: u64,
+}
+
 pub struct UiRenderState {
     pub active: HashMap<WidgetId, ActiveData>,
     pub primitives: Primitives,
@@ -115,13 +123,13 @@ impl UiRenderState {
         }
     }
 
-    pub fn take_counters(&mut self) -> (u64, u64, u64, u64) {
-        (
-            std::mem::take(&mut self.draw_count),
-            std::mem::take(&mut self.region_mut_count),
-            std::mem::take(&mut self.mov_count),
-            std::mem::take(&mut self.shape_count),
-        )
+    pub fn take_counters(&mut self) -> RenderCounters {
+        RenderCounters {
+            draws: std::mem::take(&mut self.draw_count),
+            region_rewrites: std::mem::take(&mut self.region_mut_count),
+            moves: std::mem::take(&mut self.mov_count),
+            shapes: std::mem::take(&mut self.shape_count),
+        }
     }
 
     pub(super) fn note_move(&mut self) {
diff --git a/iris/examples/bench_images.rs b/iris/examples/bench_images.rs
index 71d63a0..db4b0b5 100644
--- a/iris/examples/bench_images.rs
+++ b/iris/examples/bench_images.rs
@@ -4,24 +4,24 @@ const ROWS: usize = 1000;
 const SETTLE_FRAMES: usize = 4;
 const FRAMES: usize = 6;
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 struct State {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
     span: WeakWidget<Span>,
     frame: usize,
     appended: bool,
 }
 
-impl DefaultAppState for State {
+impl DesktopAppState for State {
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
         let mut span = Span::empty(Dir::DOWN);
         for _ in 0..ROWS {
             let img = image::DynamicImage::new_rgba8(32, 32);
-            let widget = image::<DefaultRsc<Self>>(img)(rsc);
+            let widget = image::<DesktopRsc<Self>>(img)(rsc);
             let widget = rsc.ui.widgets.add_strong(widget);
             span.push(widget.any());
         }
@@ -40,7 +40,7 @@ impl DefaultAppState for State {
         }
     }
 
-    fn window_event(&mut self, event: winit::event::WindowEvent, rsc: &mut DefaultRsc<Self>) {
+    fn window_event(&mut self, event: winit::event::WindowEvent, rsc: &mut DesktopRsc<Self>) {
         if !matches!(event, winit::event::WindowEvent::RedrawRequested) {
             return;
         }
@@ -53,7 +53,7 @@ impl DefaultAppState for State {
         if self.frame == SETTLE_FRAMES && !self.appended {
             self.appended = true;
             let img = image::DynamicImage::new_rgba8(32, 32);
-            let widget = image::<DefaultRsc<Self>>(img)(rsc);
+            let widget = image::<DesktopRsc<Self>>(img)(rsc);
             let widget = rsc.ui.widgets.add_strong(widget);
             rsc.ui
                 .widgets
@@ -71,5 +71,5 @@ impl DefaultAppState for State {
 }
 
 fn main() {
-    DefaultApp::<State>::run();
+    DesktopApp::<State>::run();
 }
diff --git a/iris/examples/message_list.rs b/iris/examples/message_list.rs
index c8da116..73712c1 100644
--- a/iris/examples/message_list.rs
+++ b/iris/examples/message_list.rs
@@ -2,12 +2,12 @@ use iris::prelude::*;
 use winit::{dpi::LogicalSize, window::WindowAttributes};
 
 fn main() {
-    DefaultApp::<State>::run();
+    DesktopApp::<State>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 struct State {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
 }
 
 const ROWS: usize = 800;
@@ -58,14 +58,14 @@ fn build_row<Rsc: UiRsc + 'static>(rsc: &mut Rsc, i: usize) -> StrongWidget {
     }
 }
 
-impl DefaultAppState for State {
+impl DesktopAppState for State {
     fn window_attributes() -> WindowAttributes {
         WindowAttributes::default().with_inner_size(LogicalSize::new(420.0, 900.0))
     }
 
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
         let mut list = LazySpan::new(Dir::DOWN, Pin::End);
diff --git a/iris/examples/minimal.rs b/iris/examples/minimal.rs
index 4484baf..50b7807 100644
--- a/iris/examples/minimal.rs
+++ b/iris/examples/minimal.rs
@@ -1,18 +1,18 @@
 use iris::prelude::*;
 
 fn main() {
-    DefaultApp::<State>::run();
+    DesktopApp::<State>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 struct State {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
 }
 
-impl DefaultAppState for State {
+impl DesktopAppState for State {
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
         rect(PaintId::RED).set_root(rsc, &mut ui_state);
diff --git a/iris/examples/tabs/main.rs b/iris/examples/tabs/main.rs
index d4d4ec9..0732297 100644
--- a/iris/examples/tabs/main.rs
+++ b/iris/examples/tabs/main.rs
@@ -2,19 +2,19 @@ use iris::prelude::*;
 use winit::event::WindowEvent;
 
 fn main() {
-    DefaultApp::<Client>::run();
+    DesktopApp::<Client>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 pub struct Client {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
     info: WeakWidget<Text>,
 }
 
-impl DefaultAppState for Client {
+impl DesktopAppState for Client {
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
         let widgets = tabs_ui::build(rsc, &mut ui_state);
@@ -24,7 +24,7 @@ impl DefaultAppState for Client {
         }
     }
 
-    fn window_event(&mut self, _: WindowEvent, rsc: &mut DefaultRsc<Self>) {
+    fn window_event(&mut self, _: WindowEvent, rsc: &mut DesktopRsc<Self>) {
         let render_state = rsc.ui.render_state();
         let new = format!(
             "widgets: {}\nactive: {}\nviews: {}",
diff --git a/iris/examples/task.rs b/iris/examples/task.rs
index b3aca61..7947832 100644
--- a/iris/examples/task.rs
+++ b/iris/examples/task.rs
@@ -2,18 +2,18 @@ use iris::prelude::*;
 use std::time::Duration;
 
 fn main() {
-    DefaultApp::<State>::run();
+    DesktopApp::<State>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 struct State {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
 }
 
-impl DefaultAppState for State {
+impl DesktopAppState for State {
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
         let rect = rect(PaintId::RED).add(rsc);
diff --git a/iris/examples/view.rs b/iris/examples/view.rs
index cbe5ea4..7a4fbc5 100644
--- a/iris/examples/view.rs
+++ b/iris/examples/view.rs
@@ -1,15 +1,15 @@
 use iris::prelude::*;
 
 fn main() {
-    DefaultApp::<State>::run();
+    DesktopApp::<State>::run();
 }
 
-#[derive(DefaultUiState)]
+#[derive(DesktopUiState)]
 struct State {
-    ui_state: DefaultUiState,
+    ui_state: DesktopUiState,
 }
 
-type Rsc = DefaultRsc<State>;
+type Rsc = DesktopRsc<State>;
 
 #[derive(Clone, Copy, WidgetView)]
 struct Test {
@@ -35,10 +35,10 @@ impl Test {
     }
 }
 
-impl DefaultAppState for State {
+impl DesktopAppState for State {
     fn new(
-        mut ui_state: DefaultUiState,
-        rsc: &mut DefaultRsc<Self>,
+        mut ui_state: DesktopUiState,
+        rsc: &mut DesktopRsc<Self>,
         _: Proxy<Self::Event>,
     ) -> Self {
         let test = Test::new(rsc);
diff --git a/iris/macro/src/lib.rs b/iris/macro/src/lib.rs
index d48908c..bdc335e 100644
--- a/iris/macro/src/lib.rs
+++ b/iris/macro/src/lib.rs
@@ -101,8 +101,8 @@ pub fn widget_trait(input: TokenStream) -> TokenStream {
     .into()
 }
 
-#[proc_macro_derive(DefaultUiState, attributes(default_ui_state))]
-pub fn derive_default_ui_state(input: TokenStream) -> TokenStream {
+#[proc_macro_derive(DesktopUiState, attributes(desktop_ui_state))]
+pub fn derive_desktop_ui_state(input: TokenStream) -> TokenStream {
     let mut output = proc_macro2::TokenStream::new();
 
     let state: ItemStruct = parse_macro_input!(input);
@@ -112,14 +112,14 @@ pub fn derive_default_ui_state(input: TokenStream) -> TokenStream {
     for field in &state.fields {
         if !found_attr
             && let Type::Path(path) = &field.ty
-            && path.path.is_ident("DefaultUiState")
+            && path.path.is_ident("DesktopUiState")
         {
             state_field = Some(field);
         }
         let Some(attr) = field
             .attrs
             .iter()
-            .find(|a| a.path().is_ident("default_ui_state"))
+            .find(|a| a.path().is_ident("desktop_ui_state"))
         else {
             continue;
         };
@@ -127,7 +127,7 @@ pub fn derive_default_ui_state(input: TokenStream) -> TokenStream {
             output.extend(
                 Error::new(
                     attr.span(),
-                    "cannot have more than one default_ui_state attribute",
+                    "cannot have more than one desktop_ui_state attribute",
                 )
                 .into_compile_error(),
             );
@@ -138,18 +138,18 @@ pub fn derive_default_ui_state(input: TokenStream) -> TokenStream {
     }
     let Some(field) = state_field else {
         output.extend(
-            Error::new(state.ident.span(), "no DefaultUiState field found").into_compile_error(),
+            Error::new(state.ident.span(), "no DesktopUiState field found").into_compile_error(),
         );
         return output.into();
     };
     let sname = &state.ident;
     let fname = field.ident.as_ref().unwrap();
     output.extend(quote! {
-        impl iris::default::HasDefaultUiState for #sname {
-            fn default_state(&self) -> &iris::default::DefaultUiState {
+        impl iris::desktop::HasDesktopUiState for #sname {
+            fn desktop_state(&self) -> &iris::desktop::DesktopUiState {
                 &self.#fname
             }
-            fn default_state_mut(&mut self) -> &mut iris::default::DefaultUiState {
+            fn desktop_state_mut(&mut self) -> &mut iris::desktop::DesktopUiState {
                 &mut self.#fname
             }
         }
diff --git a/iris/run-headless.sh b/iris/run-headless.sh
index 59d8e99..750c19e 100755
--- a/iris/run-headless.sh
+++ b/iris/run-headless.sh
@@ -18,7 +18,7 @@
 # `content_scale` 2.55, from docs/bench/iris-phone-v2-2026-09-06.md,
 # carried in `ai_app::ui::fixture::PHONE_*`), and `IRIS_SCALE` hands that
 # density to iris the way `DisplayMetrics.density` does on Android
-# (`iris::default::content_scale`). So a screenshot from here and one
+# (`iris::desktop::content_scale`). So a screenshot from here and one
 # from the phone are the same layout at the same density, and what
 # differs is only the renderer. Without it the output stays desktop-
 # shaped, which is what every other example wants.
diff --git a/iris/src/android/render.rs b/iris/src/android/render.rs
index f1c4e62..f6c20a9 100644
--- a/iris/src/android/render.rs
+++ b/iris/src/android/render.rs
@@ -176,7 +176,7 @@ impl AndroidRenderer {
             .filter(|part| !part.is_empty())
             .collect::<Vec<_>>()
             .join(" ");
-        // Say which adapter won, in the same words `default::render` uses,
+        // Say which adapter won, in the same words `desktop::render` uses,
         // and at startup rather than only on the Diagnostics page: the
         // backend alone (logged by `view.rs` when a renderer is built) does
         // not separate the cases that matter. In this checkout's emulator
diff --git a/iris/src/android/view.rs b/iris/src/android/view.rs
index 9373576..efdbfe3 100644
--- a/iris/src/android/view.rs
+++ b/iris/src/android/view.rs
@@ -11,13 +11,7 @@ use android_view::{
     },
     ndk::event::{Axis, Keycode, MotionAction},
 };
-use std::{
-    cell::RefCell,
-    marker::{PhantomData, Sized},
-    rc::Rc,
-    sync::Arc,
-    time::Instant,
-};
+use std::{cell::RefCell, marker::Sized, rc::Rc, sync::Arc, time::Instant};
 
 use super::{
     access::{AndroidAccessSource, NullActionHandler, raise_if_enabled},
@@ -25,10 +19,7 @@ use super::{
     render::{AndroidRedrawHandle, AndroidRenderer},
 };
 
-/// The android-view analogue of `default::DefaultUiState`. `renderer` is an
-/// `Option` because a `SurfaceView`'s surface does not outlive backgrounding
-/// the way a winit `Window` does -- `surfaceDestroyed`/`surfaceCreated` can
-/// happen any number of times over the life of one `IrisViewPeer`.
+/// Android host state. The renderer follows the `SurfaceView` lifecycle.
 /// How many frames after each `surface_changed` `render()` logs a full
 /// diagnostic line for -- see the log site's own comment.
 const DIAGNOSTIC_FRAMES: u64 = 10;
@@ -39,24 +30,13 @@ pub struct AndroidUiState {
     pub focus: Option<WeakWidget<TextEdit>>,
     pub cursor: CursorState,
     pub last_click: Instant,
-    /// The IME preedit's previous length, in `char`s -- the same
-    /// re-send-the-whole-composition bookkeeping `default::DefaultUiState`
-    /// keeps for winit's `Ime::Preedit`, since android-view's
-    /// `setComposingText` has the identical shape (see `android/ime.rs`).
+    /// Previous IME preedit length, in characters.
     pub compose_len: usize,
-    /// Set by `attr::FocusHost::focus_gained` when a `TextEdit` is focused;
-    /// consumed by the touch handler after the sensor pass finishes, since
-    /// showing the keyboard is a JNI call and `focus_gained` runs deep
-    /// inside the platform-agnostic sensor dispatch with no `CallbackCtx`
-    /// in reach.
+    /// Deferred until the input callback regains access to JNI.
     pub pending_show_keyboard: bool,
-    /// A URL a tapped link asked the platform to open, for the same
-    /// reason `pending_show_keyboard` is a flag rather than a call --
-    /// see `android/platform.rs`.
+    /// Also deferred until a JNI callback is available.
     pub pending_open_url: Option<String>,
-    /// Window insets, filled in from outside the normal `ViewPeer` callback
-    /// path -- see `android/insets.rs` for why they need a registry of
-    /// their own.
+    /// Filled by the native insets callback registered in `android/insets.rs`.
     shared: Rc<RefCell<Shared>>,
     pub access_adapter: AccessAdapter,
     pub access: AccessTree,
@@ -132,13 +112,7 @@ pub trait AndroidAppState: HasAndroidUiState {
     fn on_insets_changed(&mut self, rsc: &mut AndroidRsc<Self>, insets: WindowInsets) {}
 }
 
-/// `insets::Insets` as `f32`, for the widget-facing callback above -- a
-/// distinct type from `insets::Insets` so a caller of `on_insets_changed`
-/// is not coupled to that module's own (`i32`, JNI-shaped) representation.
-/// Both are physical pixels; this used to divide by `content_scale` into a
-/// separate *logical* unit (hence the old name, `LogicalInsets`), back when
-/// the rest of layout was logical too -- see `AndroidUiState::content_scale`'s
-/// field comment for why that stopgap is gone.
+/// Widget-facing insets in physical pixels, decoupled from JNI's integer shape.
 #[derive(Clone, Copy, Default, Debug, PartialEq)]
 pub struct WindowInsets {
     pub left: f32,
@@ -166,66 +140,7 @@ impl WindowInsets {
     }
 }
 
-pub struct AndroidRsc<State: 'static> {
-    pub ui: Ui,
-    pub events: EventManager<Self>,
-    pub tasks: Tasks<Self>,
-    pub state: WidgetState,
-    _state: PhantomData<State>,
-}
-
-impl<State> AndroidRsc<State> {
-    pub fn create_state<T: 'static>(&mut self, id: impl IdLike, data: T) -> WeakState<T> {
-        self.state.add(id.id(), data)
-    }
-}
-
-impl<State> UiRsc for AndroidRsc<State> {
-    fn ui(&self) -> &Ui {
-        &self.ui
-    }
-    fn ui_mut(&mut self) -> &mut Ui {
-        &mut self.ui
-    }
-    fn on_draw(&mut self, active: &ActiveData) {
-        self.events.draw(active);
-    }
-    fn on_undraw(&mut self, active: &ActiveData) {
-        self.events.undraw(active);
-    }
-    fn on_remove(&mut self, id: WidgetId) {
-        self.events.remove(id);
-        self.state.remove(id);
-    }
-}
-
-impl<State: 'static> HasState for AndroidRsc<State> {
-    type State = State;
-}
-
-impl<State: 'static> HasEvents for AndroidRsc<State> {
-    fn events(&self) -> &EventManager<Self> {
-        &self.events
-    }
-    fn events_mut(&mut self) -> &mut EventManager<Self> {
-        &mut self.events
-    }
-}
-
-impl<State: 'static> HasTasks for AndroidRsc<State> {
-    fn tasks_mut(&mut self) -> &mut Tasks<Self> {
-        &mut self.tasks
-    }
-}
-
-impl<State: 'static> HasWidgetState for AndroidRsc<State> {
-    fn widget_state(&self) -> &WidgetState {
-        &self.state
-    }
-    fn widget_state_mut(&mut self) -> &mut WidgetState {
-        &mut self.state
-    }
-}
+pub type AndroidRsc<State> = AppRsc<State>;
 
 /// The `ViewPeer` android-view dispatches every callback to. One per
 /// `RustView` instance; `new_peer` (below) builds it and hands the id to
@@ -234,30 +149,10 @@ pub struct IrisViewPeer<State: AndroidAppState> {
     pub(super) rsc: AndroidRsc<State>,
     pub(super) state: State,
     task_recv: TaskMsgReceiver<AndroidRsc<State>>,
-    /// The one ruler this view dates everything on: touch samples in
-    /// `on_touch_event` and the `Choreographer` frame time in `do_frame`.
-    /// Anchored by whichever of the two arrives first and never
-    /// re-anchored after, which is what lets a fling be advanced on the
-    /// same clock the gesture that launched it was measured on. Its path
-    /// out is the peer's own drop: it holds nothing but three numbers and
-    /// is meaningless to any other view.
+    /// Converts input and Choreographer timestamps onto one monotonic clock.
     device_clock: Option<DeviceClock>,
 }
 
-impl<State: 'static, I: RscIdx<AndroidRsc<State>>> std::ops::Index<I> for AndroidRsc<State> {
-    type Output = I::Output;
-
-    fn index(&self, index: I) -> &Self::Output {
-        index.get(self)
-    }
-}
-
-impl<State: 'static, I: RscIdx<AndroidRsc<State>>> std::ops::IndexMut<I> for AndroidRsc<State> {
-    fn index_mut(&mut self, index: I) -> &mut Self::Output {
-        index.get_mut(self)
-    }
-}
-
 impl<State: AndroidAppState> IrisViewPeer<State> {
     fn drain_tasks(&mut self) {
         while let Ok(update) = self.task_recv.try_recv() {
@@ -298,7 +193,7 @@ impl<State: AndroidAppState> IrisViewPeer<State> {
     /// Common tail for every callback that might have changed the cursor,
     /// the text focus, or the widget tree: run the sensors that touch
     /// input feeds, then ask for a frame if the result needs drawing.
-    /// Mirrors `default::DefaultApp::window_event`'s tail, split across
+    /// Mirrors `desktop::DesktopApp::window_event`'s tail, split across
     /// android-view's several entry points instead of winit's one.
     pub(super) fn after_input(&mut self, ctx: &mut CallbackCtx) {
         self.run_input_frame(ctx);
@@ -322,6 +217,42 @@ impl<State: AndroidAppState> IrisViewPeer<State> {
             .get_or_insert_with(|| DeviceClock::anchored(Instant::now(), event_time, oldest))
     }
 
+    fn generic_motion(&mut self, ctx: &mut CallbackCtx, event: &MotionEvent<'_>) -> bool {
+        let action = event.action_masked(&mut ctx.env);
+        let event_time = event.event_time_nanos(&mut ctx.env);
+        let mut clock = self.device_clock(event_time, event_time);
+        let at = clock.sample(event_time);
+        self.device_clock = Some(clock);
+
+        let ui = self.state.android_state_mut();
+        ui.cursor.time = at;
+        ui.cursor.pos = vec2(event.x(&mut ctx.env), event.y(&mut ctx.env));
+        ui.cursor.exists = !matches!(action, MotionAction::HoverExit);
+
+        let buttons = event.button_state(&mut ctx.env);
+        ui.cursor.buttons.left.update(buttons.primary());
+        ui.cursor.buttons.right.update(buttons.secondary());
+        ui.cursor.buttons.middle.update(buttons.teriary());
+
+        match action {
+            MotionAction::HoverEnter
+            | MotionAction::HoverMove
+            | MotionAction::HoverExit
+            | MotionAction::ButtonPress
+            | MotionAction::ButtonRelease => {}
+            MotionAction::Scroll => {
+                ui.cursor.scroll_delta = vec2(
+                    event.axis(&mut ctx.env, Axis::Hscroll, 0),
+                    event.axis(&mut ctx.env, Axis::Vscroll, 0),
+                );
+            }
+            _ => return false,
+        }
+
+        self.after_input(ctx);
+        true
+    }
+
     fn window_size(&self) -> Vec2 {
         let ui_state = self.state.android_state();
         match &ui_state.renderer {
@@ -514,27 +445,14 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
     ) -> bool {
         self.drain_tasks();
         let action = event.action_masked(&mut ctx.env);
-        // Device (physical) pixels, same space layout now uses throughout
-        // -- see `AndroidUiState::content_scale`'s field comment.
+        // MotionEvent and layout both use physical pixels.
         let x = event.x(&mut ctx.env);
         let y = event.y(&mut ctx.env);
-        // The event's own clock, converted through the view's one anchor
-        // -- taken on whichever of a touch or a frame callback came first.
-        // Android reports sample times in the `SystemClock.uptimeMillis()`
-        // base, which is the same `CLOCK_MONOTONIC` an `Instant` reads, so
-        // a single `(Instant, nanos)` pair converts every later sample
-        // exactly. Anchoring **once** rather than per event is what keeps
-        // the times ordered, and anchoring on the first event's *oldest*
-        // sample rather than on its own time is what keeps that event's
-        // batch from collapsing onto one instant -- `sense::DeviceClock`'s
-        // doc has both, and owns the arithmetic so it can be unit-tested
-        // off a device (`sense_tests.rs`). See `CursorState::time`.
+        // Use the event clock so batched movement keeps its real timing.
         let event_time = event.event_time_nanos(&mut ctx.env);
         let history = event.history_size(&mut ctx.env);
         let mut clock = match self.device_clock {
             Some(clock) => clock,
-            // Only the call that anchors needs the batch's oldest sample,
-            // so the JNI read for it stays off the per-event path.
             None => {
                 let oldest = if history > 0 {
                     event.historical_event_time_nanos(&mut ctx.env, 0)
@@ -544,24 +462,12 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
                 self.device_clock(event_time, oldest)
             }
         };
-        // `iris::input`'s own doc (`sense::log_input_event`): collected
-        // only when tracing is on, since this is otherwise a `Vec` per
-        // `MotionEvent` for a line nobody is reading -- the JNI reads
-        // themselves (`historical_axis`/`historical_event_time_nanos`
-        // below) already happen unconditionally, for the replay this
-        // function does regardless of tracing.
+        // Avoid allocating trace history when input tracing is disabled.
         let trace_input = crate::diagnostics::trace_enabled();
         let mut historical_ms: Vec<(u64, f32, f32)> = Vec::new();
 
         if matches!(action, MotionAction::Move) {
-            // Android documents the historical samples as oldest first and
-            // the event's own sample as the newest of the batch; everything
-            // downstream (`VelocityTracker`, `DragArbiter`'s long-press
-            // clock) assumes it, so say so here rather than at each reader.
-            // `DeviceClock::sample` is what asserts it, and it carries the
-            // last sample seen *across* events, so the first sample of
-            // every event is checked against the previous event's last one
-            // rather than against the anchor.
+            // Android orders history oldest-first; `sample` checks monotonicity.
             for pos in 0..history {
                 let hx = event.historical_axis(&mut ctx.env, Axis::X, 0, pos);
                 let hy = event.historical_axis(&mut ctx.env, Axis::Y, 0, pos);
@@ -616,6 +522,38 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
         true
     }
 
+    fn on_generic_motion_event<'local>(
+        &mut self,
+        ctx: &mut CallbackCtx<'local>,
+        event: &MotionEvent<'local>,
+    ) -> bool {
+        self.drain_tasks();
+        self.generic_motion(ctx, event)
+    }
+
+    fn on_hover_event<'local>(
+        &mut self,
+        ctx: &mut CallbackCtx<'local>,
+        event: &MotionEvent<'local>,
+    ) -> bool {
+        let action = event.action(&mut ctx.env);
+        let x = event.x(&mut ctx.env);
+        let y = event.y(&mut ctx.env);
+        let ui = self.state.android_state_mut();
+        if let Some(events) = ui
+            .access_adapter
+            .on_hover_event(&mut NullActionHandler, action, x, y)
+        {
+            ctx.push_dynamic_deferred_callback(move |env, view| {
+                raise_if_enabled(env, view, events);
+            });
+            true
+        } else {
+            self.drain_tasks();
+            self.generic_motion(ctx, event)
+        }
+    }
+
     fn on_focus_changed<'local>(
         &mut self,
         ctx: &mut CallbackCtx<'local>,
@@ -646,32 +584,10 @@ impl<State: AndroidAppState> ViewPeer for IrisViewPeer<State> {
         height: i32,
     ) {
         self.drain_tasks();
-        // The layout engine's own notion of the canvas size is separate
-        // from the wgpu surface's -- winit's backend sets it from
-        // `WindowEvent::Resized`, and there is no equivalent automatic
-        // trigger here, so this is the one place android-view's surface
-        // size has to be told to `UiRenderState` too. Missing this drew
-        // nothing but the clear colour: the widget tree laid out against
-        // whatever size `UiRenderState::new` starts at instead of the
-        // surface's real one.
-        //
-        // **Physical pixels, matching `AndroidRenderer`'s own
-        // `size()`/`resize()`/`new()`** -- `AndroidUiState::content_scale`'s
-        // field comment. This call sets `UiRenderState::output_size`, which
-        // every `rel`/`rest` length resolves against and every `abs`
-        // pixel-region compares to directly; a `dp(56)` height now folds
-        // in the density at `Len::apply_rest` time instead of this call
-        // dividing the whole window into a separate logical space, which
-        // is what used to make every `abs`-unit size (a fixed `.height(56)`
-        // in particular) mean something different from a `rest`-based one.
+        // The layout canvas and wgpu surface are separate and both use physical pixels.
         self.rsc.ui.resize((width as f32, height as f32));
 
-        // `AndroidRenderer::resize` only reconfigures the wgpu surface and
-        // rewrites the window uniform -- device, atlas, buffers and bind
-        // groups are untouched, so the glyph cache's coordinates stay
-        // valid. A genuinely new surface (after `surface_destroyed`, e.g.
-        // backgrounding) still goes through `AndroidRenderer::new` below,
-        // since `renderer` is `None` in that case.
+        // Resizing preserves GPU resources; recreating a destroyed surface does not.
         let already_live = self.state.android_state().renderer.is_some();
         log::info!(
             "iris surface: surface_changed {width}x{height} already_live={already_live} \
@@ -883,14 +799,7 @@ pub fn new_peer<'local, State: AndroidAppState>(
     let vm = env.get_java_vm().unwrap();
     let global_view = env.new_global_ref(&view.0).unwrap();
     let redraw: Arc<dyn RequestRedraw> = Arc::new(AndroidRedrawHandle::new(vm, global_view));
-    let (tasks, task_recv) = Tasks::init(redraw);
-    let mut rsc = AndroidRsc {
-        ui: Default::default(),
-        events: Default::default(),
-        tasks,
-        state: Default::default(),
-        _state: PhantomData,
-    };
+    let (mut rsc, task_recv) = AppRsc::new(redraw);
     rsc.ui.set_density(content_scale);
     let shared = Rc::new(RefCell::new(Shared::default()));
     let ui_state = AndroidUiState::new(shared.clone(), content_scale);
diff --git a/iris/src/default/access.rs b/iris/src/desktop/access.rs
similarity index 100%
rename from iris/src/default/access.rs
rename to iris/src/desktop/access.rs
diff --git a/iris/src/default/app.rs b/iris/src/desktop/app.rs
similarity index 100%
rename from iris/src/default/app.rs
rename to iris/src/desktop/app.rs
diff --git a/iris/src/default/attr.rs b/iris/src/desktop/attr.rs
similarity index 71%
rename from iris/src/default/attr.rs
rename to iris/src/desktop/attr.rs
index 5ecfa1c..74b33c0 100644
--- a/iris/src/default/attr.rs
+++ b/iris/src/desktop/attr.rs
@@ -1,21 +1,21 @@
 use crate::prelude::*;
 use winit::dpi::{PhysicalPosition, PhysicalSize};
 
-impl<T: HasDefaultUiState> FocusHost for T {
+impl<T: HasDesktopUiState> FocusHost for T {
     fn recent_click(&mut self) -> bool {
-        crate::attr::recent_click(&mut self.default_state_mut().last_click)
+        crate::attr::recent_click(&mut self.desktop_state_mut().last_click)
     }
 
     fn set_focus(&mut self, id: Option<WeakWidget<TextEdit>>) {
-        self.default_state_mut().focus = id;
+        self.desktop_state_mut().focus = id;
     }
 
     fn is_focused(&self, id: WeakWidget<TextEdit>) -> bool {
-        self.default_state().focus == Some(id)
+        self.desktop_state().focus == Some(id)
     }
 
     fn focus_gained(&mut self, region: Option<PixelRegion>) {
-        let state = self.default_state_mut();
+        let state = self.desktop_state_mut();
         let Some(region) = region else { return };
         state.window.set_ime_allowed(true);
         state.window.set_ime_cursor_area(
diff --git a/iris/src/default/input.rs b/iris/src/desktop/input.rs
similarity index 96%
rename from iris/src/default/input.rs
rename to iris/src/desktop/input.rs
index 45d2297..6dbbc66 100644
--- a/iris/src/default/input.rs
+++ b/iris/src/desktop/input.rs
@@ -19,7 +19,7 @@ pub struct Input {
 impl Input {
     /// winit's pointer coordinates are physical pixels, which is the
     /// space the whole tree is laid out and hit-tested in -- see
-    /// `default::content_scale`. Nothing is converted here; `dp(...)`
+    /// `desktop::content_scale`. Nothing is converted here; `dp(...)`
     /// resolves against the density at layout time instead.
     pub fn event(&mut self, event: &WindowEvent) -> bool {
         match event {
@@ -79,10 +79,10 @@ impl Input {
     }
 }
 
-impl DefaultUiState {
+impl DesktopUiState {
     /// Physical pixels, matching `WindowEvent::Resized` (what
     /// `UiRenderState::resize` is given) and the swapchain -- see
-    /// `default::content_scale`.
+    /// `desktop::content_scale`.
     pub fn window_size(&self) -> Vec2 {
         let size = self.renderer.window().inner_size();
         Vec2::new(size.width as f32, size.height as f32)
diff --git a/iris/src/default/logging.rs b/iris/src/desktop/logging.rs
similarity index 100%
rename from iris/src/default/logging.rs
rename to iris/src/desktop/logging.rs
diff --git a/iris/src/default/mod.rs b/iris/src/desktop/mod.rs
similarity index 63%
rename from iris/src/default/mod.rs
rename to iris/src/desktop/mod.rs
index 765b10e..62b2808 100644
--- a/iris/src/default/mod.rs
+++ b/iris/src/desktop/mod.rs
@@ -1,10 +1,6 @@
 use crate::prelude::*;
 use arboard::Clipboard;
-use std::{
-    marker::{PhantomData, Sized},
-    sync::Arc,
-    time::Instant,
-};
+use std::{marker::Sized, sync::Arc, time::Instant};
 use winit::{
     event::{Ime, WindowEvent},
     event_loop::{ActiveEventLoop, EventLoopProxy},
@@ -26,19 +22,8 @@ pub use render::*;
 
 pub type Proxy<Event> = EventLoopProxy<Event>;
 
-/// The desktop's `content_scale`: physical pixels per dp, the same
-/// quantity Android reads from `DisplayMetrics.density` and feeds to
-/// `UiRenderState::set_density` (`android::view::AndroidUiState::
-/// content_scale`'s field comment). Everything in this backend is
-/// physical pixels -- the window size, the pointer, the widget tree --
-/// and `dp(...)` is what resolves against this at layout time, exactly
-/// as on the phone. That is a correction from an earlier version that
-/// divided winit's coordinates into a separate "logical" space instead:
-/// it left `UiRenderState::resize` (physical, from `WindowEvent::
-/// Resized`) and the window uniform (logical) disagreeing on any
-/// display whose scale factor is not 1.0, and it rasterised glyphs at
-/// one resolution to display them at another -- the blur the phone's own
-/// stopgap produced before `dp` existed.
+/// Physical pixels per dp. Layout and input stay in physical pixels; only
+/// `dp(...)` resolves through this scale.
 pub fn content_scale(window: &Window) -> f32 {
     match std::env::var("IRIS_SCALE") {
         Err(_) => window.scale_factor() as f32,
@@ -52,7 +37,7 @@ pub fn content_scale(window: &Window) -> f32 {
     }
 }
 
-pub struct DefaultUiState {
+pub struct DesktopUiState {
     pub root: Option<StrongWidget>,
     pub renderer: UiRenderer,
     pub input: Input,
@@ -65,13 +50,13 @@ pub struct DefaultUiState {
     pub access: AccessTree,
 }
 
-impl<State: 'static> HasRoot<DefaultRsc<State>> for DefaultUiState {
-    fn set_root(&mut self, rsc: &mut DefaultRsc<State>, root: StrongWidget) {
+impl<State: 'static> HasRoot<DesktopRsc<State>> for DesktopUiState {
+    fn set_root(&mut self, rsc: &mut DesktopRsc<State>, root: StrongWidget) {
         self.root = Some(crate::overlay::default_overlay_root(rsc, root));
     }
 }
 
-impl DefaultUiState {
+impl DesktopUiState {
     pub fn new(window: impl Into<Arc<Window>>, access_adapter: accesskit_winit::Adapter) -> Self {
         let window = window.into();
         Self {
@@ -89,114 +74,35 @@ impl DefaultUiState {
     }
 }
 
-pub trait HasDefaultUiState: Sized + 'static {
-    fn default_state(&self) -> &DefaultUiState;
-    fn default_state_mut(&mut self) -> &mut DefaultUiState;
+pub trait HasDesktopUiState: Sized + 'static {
+    fn desktop_state(&self) -> &DesktopUiState;
+    fn desktop_state_mut(&mut self) -> &mut DesktopUiState;
 }
 
-pub trait DefaultAppState: HasDefaultUiState {
+pub trait DesktopAppState: HasDesktopUiState {
     type Event = ();
-    fn new(ui_state: DefaultUiState, rsc: &mut DefaultRsc<Self>, proxy: Proxy<Self::Event>)
+    fn new(ui_state: DesktopUiState, rsc: &mut DesktopRsc<Self>, proxy: Proxy<Self::Event>)
     -> Self;
     #[allow(unused_variables)]
-    fn event(&mut self, event: Self::Event, rsc: &mut DefaultRsc<Self>) {}
+    fn event(&mut self, event: Self::Event, rsc: &mut DesktopRsc<Self>) {}
     #[allow(unused_variables)]
-    fn exit(&mut self, rsc: &mut DefaultRsc<Self>) {}
+    fn exit(&mut self, rsc: &mut DesktopRsc<Self>) {}
     #[allow(unused_variables)]
-    fn window_event(&mut self, event: WindowEvent, rsc: &mut DefaultRsc<Self>) {}
+    fn window_event(&mut self, event: WindowEvent, rsc: &mut DesktopRsc<Self>) {}
     fn window_attributes() -> WindowAttributes {
         Default::default()
     }
 }
 
-pub struct DefaultRsc<State: 'static> {
-    pub ui: Ui,
-    pub events: EventManager<Self>,
-    pub tasks: Tasks<Self>,
-    pub state: WidgetState,
-    _state: PhantomData<State>,
-}
+pub type DesktopRsc<State> = AppRsc<State>;
 
-impl<State> DefaultRsc<State> {
-    fn init(window: Arc<Window>) -> (Self, TaskMsgReceiver<Self>) {
-        let (tasks, recv) = Tasks::init(window);
-        (
-            Self {
-                ui: Default::default(),
-                events: Default::default(),
-                tasks,
-                state: Default::default(),
-                _state: Default::default(),
-            },
-            recv,
-        )
-    }
-
-    pub fn create_state<T: 'static>(&mut self, id: impl IdLike, data: T) -> WeakState<T> {
-        self.state.add(id.id(), data)
-    }
-}
-
-impl<State> UiRsc for DefaultRsc<State> {
-    fn ui(&self) -> &Ui {
-        &self.ui
-    }
-
-    fn ui_mut(&mut self) -> &mut Ui {
-        &mut self.ui
-    }
-
-    fn on_draw(&mut self, active: &ActiveData) {
-        self.events.draw(active);
-    }
-
-    fn on_undraw(&mut self, active: &ActiveData) {
-        self.events.undraw(active);
-    }
-
-    fn on_remove(&mut self, id: WidgetId) {
-        self.events.remove(id);
-        self.state.remove(id);
-    }
-}
-
-impl<State: 'static> HasState for DefaultRsc<State> {
-    type State = State;
-}
-
-impl<State: 'static> HasEvents for DefaultRsc<State> {
-    fn events(&self) -> &EventManager<Self> {
-        &self.events
-    }
-
-    fn events_mut(&mut self) -> &mut EventManager<Self> {
-        &mut self.events
-    }
-}
-
-impl<State: 'static> HasTasks for DefaultRsc<State> {
-    fn tasks_mut(&mut self) -> &mut Tasks<Self> {
-        &mut self.tasks
-    }
-}
-
-impl<State: 'static> HasWidgetState for DefaultRsc<State> {
-    fn widget_state(&self) -> &WidgetState {
-        &self.state
-    }
-
-    fn widget_state_mut(&mut self) -> &mut WidgetState {
-        &mut self.state
-    }
-}
-
-pub struct DefaultApp<State: DefaultAppState> {
-    rsc: DefaultRsc<State>,
+pub struct DesktopApp<State: DesktopAppState> {
+    rsc: DesktopRsc<State>,
     state: State,
-    task_recv: TaskMsgReceiver<DefaultRsc<State>>,
+    task_recv: TaskMsgReceiver<DesktopRsc<State>>,
 }
 
-impl<State: DefaultAppState> AppState for DefaultApp<State> {
+impl<State: DesktopAppState> AppState for DesktopApp<State> {
     type Event = State::Event;
 
     fn new(event_loop: &ActiveEventLoop, proxy: EventLoopProxy<Self::Event>) -> Self {
@@ -211,16 +117,12 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             NullDeactivationHandler,
         );
         window.set_visible(true);
-        let default_state = DefaultUiState::new(window, access_adapter);
-        let (mut rsc, task_recv) = DefaultRsc::init(default_state.window.clone());
-        // Both copies of the density, set before the first widget is
-        // built so text shapes at the right size on the opening frame --
-        // the same pair `android::view::new_peer` sets from
-        // `content_scale`. See `iris_core::TextData::density` for why the
-        // shaper keeps its own.
-        let scale = content_scale(default_state.window.as_ref());
+        let desktop_state = DesktopUiState::new(window, access_adapter);
+        let (mut rsc, task_recv) = AppRsc::new(desktop_state.window.clone());
+        // Set before building widgets so the first text shape uses the right density.
+        let scale = content_scale(desktop_state.window.as_ref());
         rsc.ui.set_density(scale);
-        let state = State::new(default_state, &mut rsc, proxy);
+        let state = State::new(desktop_state, &mut rsc, proxy);
         Self {
             rsc,
             state,
@@ -243,7 +145,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             update(state, rsc);
         }
 
-        let ui_state = state.default_state_mut();
+        let ui_state = state.desktop_state_mut();
         // Required by `accesskit_winit` on every window event, not just the
         // ones this backend otherwise cares about -- some platform adapters
         // rely on it to notice activation (a screen reader turning on).
@@ -257,14 +159,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             ui_state.focus = None;
         }
         if input_changed {
-            // The winit half of `iris::input` (`sense::log_input_event`'s
-            // own doc): no batching here, so `historical` is always empty
-            // -- winit hands one `WindowEvent` per pointer sample, unlike
-            // Android's `MotionEvent`. The action is read back off the
-            // buttons `Input::event` just updated, the same test
-            // `GestureOutcome`'s callers already use to tell a press from a
-            // release. Computed only when tracing is on, same reasoning as
-            // `log_input_event` itself gating on it.
+            // Winit delivers one sample at a time, so there is no history batch.
             if crate::diagnostics::trace_enabled() {
                 let action = if cursor_state.buttons.left.is_start() {
                     "down"
@@ -292,7 +187,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
                 .get()
                 .run_sensors(rsc, state, cursor_state, window_size);
         }
-        let ui_state = state.default_state_mut();
+        let ui_state = state.desktop_state_mut();
         if old != ui_state.focus
             && let Some(old) = old
         {
@@ -301,16 +196,10 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
         match &event {
             WindowEvent::CloseRequested => event_loop.exit(),
             WindowEvent::RedrawRequested => {
-                // Before the draw, so this frame shows this instant's
-                // position (`UiData::tick_animations`' own doc), and the
-                // window is asked for another frame while anything is
-                // still moving -- the winit half of what
-                // `IrisViewPeer::render`'s `post_frame_callback` does on
-                // Android. Nothing else in iris moves without an input
-                // event.
+                // Advance animations before drawing and keep requesting frames while active.
                 let frame_start = std::time::Instant::now();
                 let animating = rsc.ui_mut().tick_animations(frame_start);
-                let ui_state = state.default_state_mut();
+                let ui_state = state.desktop_state_mut();
                 if animating {
                     ui_state.window.request_redraw();
                 }
@@ -415,7 +304,7 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             _ => (),
         }
         state.window_event(event, rsc);
-        let ui_state = self.state.default_state_mut();
+        let ui_state = self.state.desktop_state_mut();
         let render_state = rsc.ui.render_state();
         if render_state
             .get()
@@ -430,17 +319,3 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
         self.state.exit(&mut self.rsc);
     }
 }
-
-impl<State: 'static, I: RscIdx<DefaultRsc<State>>> std::ops::Index<I> for DefaultRsc<State> {
-    type Output = I::Output;
-
-    fn index(&self, index: I) -> &Self::Output {
-        index.get(self)
-    }
-}
-
-impl<State: 'static, I: RscIdx<DefaultRsc<State>>> std::ops::IndexMut<I> for DefaultRsc<State> {
-    fn index_mut(&mut self, index: I) -> &mut Self::Output {
-        index.get_mut(self)
-    }
-}
diff --git a/iris/src/default/platform.rs b/iris/src/desktop/platform.rs
similarity index 87%
rename from iris/src/default/platform.rs
rename to iris/src/desktop/platform.rs
index 3ed1281..993f349 100644
--- a/iris/src/default/platform.rs
+++ b/iris/src/desktop/platform.rs
@@ -1,7 +1,7 @@
 use crate::platform::OpenUrl;
-use crate::prelude::HasDefaultUiState;
+use crate::prelude::HasDesktopUiState;
 
-impl<T: HasDefaultUiState> OpenUrl for T {
+impl<T: HasDesktopUiState> OpenUrl for T {
     fn open_url(&mut self, url: &str) {
         let (program, first): (&str, &[&str]) = if cfg!(target_os = "macos") {
             ("open", &[])
diff --git a/iris/src/default/render.rs b/iris/src/desktop/render.rs
similarity index 99%
rename from iris/src/default/render.rs
rename to iris/src/desktop/render.rs
index 4fa3103..ad83302 100644
--- a/iris/src/default/render.rs
+++ b/iris/src/desktop/render.rs
@@ -213,7 +213,7 @@ impl UiRenderer {
         // that function's doc comment).
         // Physical size, the same units the swapchain, `WindowEvent::
         // Resized`, the pointer and the widget tree all use -- see
-        // `default::content_scale` for why this backend stopped dividing
+        // `desktop::content_scale` for why this backend stopped dividing
         // into a separate logical space, and what disagreed while it did.
         let physical_size = Vec2::new(size.width as f32, size.height as f32);
         let ui = UiRenderNode::new(&device, &queue, formats.view, physical_size)
diff --git a/iris/src/diagnostics.rs b/iris/src/diagnostics.rs
index 44fd8e7..ea57a2c 100644
--- a/iris/src/diagnostics.rs
+++ b/iris/src/diagnostics.rs
@@ -15,7 +15,7 @@ pub fn trace_enabled() -> bool {
 
 /// One `iris::frame` line, called once per frame from each backend's own
 /// frame function -- `android::view::IrisViewPeer::render`,
-/// `default::DefaultApp::window_event`'s `RedrawRequested` arm, and
+/// `desktop::DesktopApp::window_event`'s `RedrawRequested` arm, and
 /// `harness::Harness::frame` -- after the draw (or, on the harness, where a
 /// draw would be; `draw` is `Duration::ZERO` there since nothing is
 /// actually submitted to a GPU).
diff --git a/iris/src/harness.rs b/iris/src/harness.rs
index 56f4ab1..a044c80 100644
--- a/iris/src/harness.rs
+++ b/iris/src/harness.rs
@@ -1,5 +1,4 @@
 use crate::prelude::*;
-use std::marker::PhantomData;
 use std::sync::Arc;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::time::{Duration, Instant};
@@ -164,76 +163,7 @@ impl OpenUrl for HarnessState {
     }
 }
 
-/// The harness's `Rsc` -- identical in substance to `DefaultRsc`/
-/// `AndroidRsc` minus the windowing, for the same reason those two are
-/// separate types (`AndroidRsc`'s own doc).
-pub struct HarnessRsc {
-    pub ui: Ui,
-    pub events: EventManager<Self>,
-    pub tasks: Tasks<Self>,
-    pub state: WidgetState,
-    _state: PhantomData<HarnessState>,
-}
-
-impl UiRsc for HarnessRsc {
-    fn ui(&self) -> &Ui {
-        &self.ui
-    }
-    fn ui_mut(&mut self) -> &mut Ui {
-        &mut self.ui
-    }
-    fn on_draw(&mut self, active: &ActiveData) {
-        self.events.draw(active);
-    }
-    fn on_undraw(&mut self, active: &ActiveData) {
-        self.events.undraw(active);
-    }
-    fn on_remove(&mut self, id: WidgetId) {
-        self.events.remove(id);
-        self.state.remove(id);
-    }
-}
-
-impl HasState for HarnessRsc {
-    type State = HarnessState;
-}
-
-impl HasEvents for HarnessRsc {
-    fn events(&self) -> &EventManager<Self> {
-        &self.events
-    }
-    fn events_mut(&mut self) -> &mut EventManager<Self> {
-        &mut self.events
-    }
-}
-
-impl HasTasks for HarnessRsc {
-    fn tasks_mut(&mut self) -> &mut Tasks<Self> {
-        &mut self.tasks
-    }
-}
-
-impl HasWidgetState for HarnessRsc {
-    fn widget_state(&self) -> &WidgetState {
-        &self.state
-    }
-    fn widget_state_mut(&mut self) -> &mut WidgetState {
-        &mut self.state
-    }
-}
-
-impl<I: RscIdx<HarnessRsc>> std::ops::Index<I> for HarnessRsc {
-    type Output = I::Output;
-    fn index(&self, index: I) -> &Self::Output {
-        index.get(self)
-    }
-}
-
-impl<I: RscIdx<HarnessRsc>> std::ops::IndexMut<I> for HarnessRsc {
-    fn index_mut(&mut self, index: I) -> &mut Self::Output {
-        index.get_mut(self)
-    }
-}
+pub type HarnessRsc = AppRsc<HarnessState>;
 
 /// A screen running with no window: the widget tree, the frame loop and
 /// the pointer, all advanced by the caller. See the module doc.
@@ -255,14 +185,7 @@ impl Harness {
     /// `PHONE_SCALE`.
     pub fn new(size: Vec2, density: f32) -> Self {
         let redraws = Arc::new(RedrawCounter::default());
-        let (tasks, task_recv) = Tasks::init(redraws.clone());
-        let mut rsc = HarnessRsc {
-            ui: Ui::default(),
-            events: EventManager::default(),
-            tasks,
-            state: WidgetState::default(),
-            _state: PhantomData,
-        };
+        let (mut rsc, task_recv) = AppRsc::new(redraws.clone());
         rsc.ui.set_density(density);
         rsc.ui.resize(size);
         Self {
diff --git a/iris/src/layout_tests.rs b/iris/src/layout_tests.rs
index 04e02d7..7427494 100644
--- a/iris/src/layout_tests.rs
+++ b/iris/src/layout_tests.rs
@@ -115,7 +115,7 @@ fn a_widget_retains_its_entry_layer_not_its_child_cursor() {
     rsc.ui.widgets.get_mut(&outer_weak).unwrap().x = None;
     render.update(&root, &mut rsc);
     assert_eq!(
-        render.take_counters().0,
+        render.take_counters().draws,
         1,
         "redrawing the parent should retain the unchanged Stack subtree"
     );
@@ -250,7 +250,12 @@ fn a_child_coordinate_offset_moves_only_the_child_subtree() {
     rsc.ui.widgets.get_mut(&parent_weak).unwrap().offset.y = 35.0;
     rsc.ui.widgets.get_mut(&outer_weak).unwrap().x = None;
     render.update(&root, &mut rsc);
-    let (draws, rewrites, moves, _shapes) = render.take_counters();
+    let RenderCounters {
+        draws,
+        region_rewrites: rewrites,
+        moves,
+        ..
+    } = render.take_counters();
     let parent_after = render.window_region(&parent_weak, &rsc).unwrap();
     let child_after = render.window_region(&child_weak, &rsc).unwrap();
 
@@ -283,7 +288,7 @@ fn a_hinted_rest_draws_once_and_only_moves_the_fixed_child_after_it() {
     let mut render = UiRenderState::new();
     render.resize((200.0, 300.0));
     render.update(&root, &mut rsc);
-    let (draws, _rewrites, moves, _shapes) = render.take_counters();
+    let RenderCounters { draws, moves, .. } = render.take_counters();
 
     assert_eq!(draws, 5);
     assert_eq!(moves, 1);
@@ -328,7 +333,12 @@ fn an_unchanged_frame_draws_and_rewrites_nothing() {
     render.take_counters(); // discard the first, real draws
 
     render.update(&root, &mut rsc);
-    let (draws, rewrites, moves, _shapes) = render.take_counters();
+    let RenderCounters {
+        draws,
+        region_rewrites: rewrites,
+        moves,
+        ..
+    } = render.take_counters();
     assert_eq!((draws, rewrites, moves), (0, 0, 0));
 }
 
@@ -346,7 +356,7 @@ fn scrolling_moves_in_o1_without_a_redraw() {
 
     rsc.ui.widgets.get_mut(&scroll).unwrap().scroll(-40.0);
     render.update(&root, &mut rsc);
-    let (draws, _rewrites, moves, _shapes) = render.take_counters();
+    let RenderCounters { draws, moves, .. } = render.take_counters();
 
     assert_eq!(draws, 1, "only Scroll itself should redraw");
     assert_eq!(moves, 1, "the scrolled subtree should move in one write");
diff --git a/iris/src/lib.rs b/iris/src/lib.rs
index b7dd1fd..5144d22 100644
--- a/iris/src/lib.rs
+++ b/iris/src/lib.rs
@@ -1,6 +1,6 @@
 #![feature(unboxed_closures)]
 #![feature(fn_traits)]
-// Only `default::DefaultAppState::Event`'s default uses this; unused (and
+// Only `desktop::DesktopAppState::Event`'s default uses this; unused (and
 // warned about) on the android target, which has no such default.
 #![cfg_attr(not(target_os = "android"), feature(associated_type_defaults))]
 #![feature(unsize)]
@@ -10,7 +10,7 @@
 #[cfg(target_os = "android")]
 pub mod android;
 #[cfg(not(target_os = "android"))]
-pub mod default;
+pub mod desktop;
 
 pub mod attr;
 pub mod diagnostics;
@@ -18,6 +18,7 @@ pub mod event;
 pub mod harness;
 pub mod overlay;
 pub mod platform;
+pub mod runtime;
 pub mod sense;
 pub mod state;
 pub mod task;
@@ -38,7 +39,7 @@ pub mod prelude {
     #[cfg(target_os = "android")]
     pub use android::*;
     #[cfg(not(target_os = "android"))]
-    pub use default::*;
+    pub use desktop::*;
 
     pub use attr::*;
     pub use event::*;
@@ -46,6 +47,7 @@ pub mod prelude {
     pub use iris_macro::*;
     pub use overlay::*;
     pub use platform::*;
+    pub use runtime::*;
     pub use sense::*;
     pub use state::*;
     pub use task::*;
diff --git a/iris/src/runtime.rs b/iris/src/runtime.rs
new file mode 100644
index 0000000..b3a2c79
--- /dev/null
+++ b/iris/src/runtime.rs
@@ -0,0 +1,98 @@
+use crate::prelude::*;
+use std::sync::Arc;
+
+/// Resources shared by every Iris host.
+pub struct AppRsc<State: 'static> {
+    pub ui: Ui,
+    pub events: EventManager<Self>,
+    pub tasks: Tasks<Self>,
+    pub state: WidgetState,
+    _state: std::marker::PhantomData<State>,
+}
+
+impl<State> AppRsc<State> {
+    pub(crate) fn new(redraw: Arc<dyn RequestRedraw>) -> (Self, TaskMsgReceiver<Self>) {
+        let (tasks, receiver) = Tasks::init(redraw);
+        (
+            Self {
+                ui: Ui::default(),
+                events: EventManager::default(),
+                tasks,
+                state: WidgetState::default(),
+                _state: std::marker::PhantomData,
+            },
+            receiver,
+        )
+    }
+
+    pub fn create_state<T: 'static>(&mut self, id: impl IdLike, data: T) -> WeakState<T> {
+        self.state.add(id.id(), data)
+    }
+}
+
+impl<State> UiRsc for AppRsc<State> {
+    fn ui(&self) -> &Ui {
+        &self.ui
+    }
+
+    fn ui_mut(&mut self) -> &mut Ui {
+        &mut self.ui
+    }
+
+    fn on_draw(&mut self, active: &ActiveData) {
+        self.events.draw(active);
+    }
+
+    fn on_undraw(&mut self, active: &ActiveData) {
+        self.events.undraw(active);
+    }
+
+    fn on_remove(&mut self, id: WidgetId) {
+        self.events.remove(id);
+        self.state.remove(id);
+    }
+}
+
+impl<State> HasState for AppRsc<State> {
+    type State = State;
+}
+
+impl<State> HasEvents for AppRsc<State> {
+    fn events(&self) -> &EventManager<Self> {
+        &self.events
+    }
+
+    fn events_mut(&mut self) -> &mut EventManager<Self> {
+        &mut self.events
+    }
+}
+
+impl<State> HasTasks for AppRsc<State> {
+    fn tasks_mut(&mut self) -> &mut Tasks<Self> {
+        &mut self.tasks
+    }
+}
+
+impl<State> HasWidgetState for AppRsc<State> {
+    fn widget_state(&self) -> &WidgetState {
+        &self.state
+    }
+
+    fn widget_state_mut(&mut self) -> &mut WidgetState {
+        &mut self.state
+    }
+}
+
+impl<State, I: RscIdx<AppRsc<State>>> std::ops::Index<I> for AppRsc<State> {
+    type Output = I::Output;
+
+    fn index(&self, index: I) -> &Self::Output {
+        index.get(self)
+    }
+}
+
+impl<State, I: RscIdx<AppRsc<State>>> std::ops::IndexMut<I> for AppRsc<State> {
+    fn index_mut(&mut self, index: I) -> &mut Self::Output {
+        index.get_mut(self)
+    }
+}
diff --git a/iris/src/widget/position/lazy_span.rs b/iris/src/widget/position/lazy_span.rs
index bedaed8..7897edb 100644
--- a/iris/src/widget/position/lazy_span.rs
+++ b/iris/src/widget/position/lazy_span.rs
@@ -1155,7 +1155,7 @@ mod tests {
                 .push_front(LazyItem::new(key, w));
         }
         render.update(&root, &mut rsc);
-        let (draws, _rewrites, _moves, _shapes) = render.take_counters();
+        let draws = render.take_counters().draws;
 
         let extents_after = rsc.ui.widgets.get(&list_weak).unwrap().extents.clone();
         for key in [11u64, 12] {
@@ -1269,7 +1269,8 @@ mod tests {
 
             rsc.ui.widgets.get_mut(&list_weak).unwrap().scroll(1.0);
             render.update(&root, &mut rsc);
-            let (draws, _rewrites, moves, _shapes) = render.take_counters();
+            let counters = render.take_counters();
+            let (draws, moves) = (counters.draws, counters.moves);
 
             assert_eq!(draws, 1, "n={n}: only the list should really draw");
             assert_eq!(moves, 1, "n={n}: the whole retained run should move once");