fix(tauri-app): kill effect_update_depth_exceeded via untrack + setView

Two independent Svelte 5 effect-loop bugs that triggered the
same 'effect_update_depth_exceeded' guard:

1. PostCard.svelte: the embed-quote-fetch $effect and the
   likedBox $effect.pre read a state variable (quotedLoading /
   likedBox) and then synchronously wrote to it in the same
   effect run. Svelte 5's effect tracker schedules
   possible_effect_self_invalidation on the touched state, the
   effect re-fires immediately, and the cycle trips the
   'flush_count > 1000' guard. With ~30 PostCards mounting on
   login the per-card loop compounds into the depth exceeded
   error. Wrap the read+write blocks in untrack() so the
   hydration flags don't contribute to the effect's dep set;
   the outer 'post.embed.uri / post.did / post.rkey' reads
   remain tracked so navigation between cards still triggers a
   fresh hydrate.

2. App.svelte: the four $effect blocks (home-refresh,
   home-poll, profile-refresh, search-debounce) lived and died
   together. Even after splitting, Svelte 5 still flagged the
   call chain into refreshTimeline / refreshProfile because
   their sync prelude writes 'timelineLoading = true' /
   'profileLoading = true' while the effect already tracks the
   same downstream state via the proxy. Drive everything
   imperatively through a single setView(v) function and move
   the 5s poll into the session.subscribe callback, which fires
   only on actual login/logout transitions. setView is the
   single point that flips view AND triggers the right refresh
   per destination — NavRail on_select, LoginScreen onLogin,
   handleLogout, the 'back to timeline' button, and the tray
   navigate-event bridge all route through it now.

Also: NavRail and StatusBar self-style their grid-area in
their own component styles ('grid-area: rail' / 'status') so
App.svelte doesn't need the fragile '$state.s-XXX > nav.rail'
cross-component selector that Svelte 5 was failing to match
in the Tauri webview, leaving rail buttons invisible to clicks.

crates/tauri-app/src/App.svelte

@@ -34,7 +34,6 @@
   let timelineError: string | null = $state(null);
   let seenUris: Set<string> = new Set();
   let _statusTimer: number | undefined;
-  let _timelinePollTimer: number | undefined;
 
   // Profile state.
   let profile: ProfileResponse | null = $state(null);
@@ -93,7 +92,7 @@
   // — `main.ts` is the only place that wires to the Tauri event bus).
   function onNavigateToView(e: Event) {
     const detail = (e as CustomEvent<{ view: View }>).detail;
-    if (detail?.view) view = detail.view;
+    if (detail?.view) setView(detail.view);
   }
   function onNotification(e: Event) {
     const detail = (e as CustomEvent<{ title: string; body: string; url: string | null }>).detail;
@@ -133,7 +132,7 @@
       }
     } else {
       // unknown scheme — just open home
-      view = "home";
+      setView("home");
     }
   }
 
@@ -186,7 +185,7 @@
     registerCleanup(() => {
       if (_sessionUnsub) _sessionUnsub();
       if (_statusTimer) clearInterval(_statusTimer);
-      if (_timelinePollTimer) clearInterval(_timelinePollTimer);
+      if (_pollTimer != null) clearInterval(_pollTimer);
       if (_searchDebounce) clearTimeout(_searchDebounce);
       if (typeof window !== "undefined") {
         window.removeEventListener("maarcadetweet:toast", _toastHandler);
@@ -201,6 +200,11 @@
       _sessionUnsub = session.subscribe((s) => {
         currentUser = s;
         status = { ...status, did: s?.did, handle: s?.handle, authenticated: !!s };
+        // Drive the 5s poll off the session lifecycle instead of a
+        // reactive effect — the effect form kept tripping Svelte 5's
+        // depth guard.
+        if (s) startPoll();
+        else stopPoll();
       });
 
       if (typeof window !== "undefined") {
@@ -221,29 +225,48 @@
     })();
   });
 
-  // Re-fetch the home timeline whenever we navigate to "home" or
+  // Imperative view-switching. We dispatch from a single function
-  // when the logged-in user changes. We also poll every 5s while
+  // (called by NavRail on_select, the LoginScreen onLogin path, and
-  // the home view is active so new posts trickle in.
+  // the tray-event bridge) so every view transition runs the same
-  $effect(() => {
+  // side effects in one place. Previously this was four separate
-    if (view === "home" && currentUser) {
+  // `$effect` blocks that read `view` / `currentUser` and called
+  // `refreshTimeline` / `refreshProfile` / `scheduleSearch`. Svelte
+  // 5's depth tracker kept aborting with `effect_update_depth_exceeded`
+  // because the sync portions of those refresh functions (`timelineLoading
+  // = true`, `profileLoading = true`) wrote $state that the effect's
+  // proxy-tracking had flagged as a self-write. Driving everything
+  // imperatively from a setter sidesteps the reactive cycle.
+  function setView(next: View) {
+    const prev = view;
+    view = next;
+    if (!currentUser) return;
+
+    // Entering home from elsewhere — pull a fresh timeline and
+    // (re)start the poll timer. Leaving home clears it.
+    if (next === "home" && prev !== "home") {
       void refreshTimeline(true);
-      if (_timelinePollTimer) clearInterval(_timelinePollTimer);
-      _timelinePollTimer = window.setInterval(() => {
-        void refreshTimeline(false); // poll = prepend new posts, don't wipe
-      }, 5000);
-    } else if (_timelinePollTimer) {
-      clearInterval(_timelinePollTimer);
-      _timelinePollTimer = undefined;
     }
-
+    if (next === "profile") {
-    if (view === "profile" && currentUser) {
+      const handle = currentUser.handle;
-      void refreshProfile(currentUser.handle);
+      void refreshProfile(handle);
     }
-
+    if (next === "search" && searchQuery.trim().length > 0) {
-    if (view === "search" && currentUser && searchQuery.trim().length > 0) {
       scheduleSearch();
     }
-  });
+  }
+
+  let _pollTimer: number | undefined;
+  function startPoll() {
+    if (_pollTimer != null) return;
+    _pollTimer = window.setInterval(() => {
+      if (view === "home") void refreshTimeline(false);
+    }, 5000);
+  }
+  function stopPoll() {
+    if (_pollTimer == null) return;
+    window.clearInterval(_pollTimer);
+    _pollTimer = undefined;
+  }
 
   async function refreshTimeline(reset: boolean) {
     if (!currentUser) return;
@@ -356,7 +379,7 @@
   async function handleLogout() {
     try {
       await session.logout();
-      view = "home";
+      setView("home");
       profile = null;
       searchResults = [];
       threadRoot = null;
@@ -400,7 +423,7 @@
     <LoginScreen
       onLogin={(s) => {
         currentUser = s;
-        view = "home";
+        setView("home");
       }}
     />
   </div>
@@ -408,9 +431,7 @@
   <div class="shell">
     <NavRail
       {view}
-      on_select={(v) => {
+      on_select={(v) => setView(v)}
-        view = v;
-      }}
     />
     <div class="main">
       <Terminal title={view === "home" ? "maarcadetweet — home" : `maarcadetweet — ${view}`}>
@@ -580,7 +601,7 @@
               <button
                 class="btn btn--ghost"
                 type="button"
-                onclick={() => (view = "home")}
+                onclick={() => setView("home")}
               >← back to timeline</button>
             </div>
 
@@ -720,8 +741,11 @@
       "rail status";
     min-height: 0;
   }
-  .shell > :global(nav.rail) { grid-area: rail; }
+  /* NavRail and StatusBar self-assign their own grid-area
-  .shell > :global(.statusbar) { grid-area: status; }
+     (`grid-area: rail` / `grid-area: status`) in their component
+     styles, so the parent doesn't need any :global() child
+     selectors. The `.main` slot is just the next sibling; we set
+     its grid-area explicitly below. */
   .main {
     grid-area: main;
     overflow: auto;

crates/tauri-app/src/lib/components/NavRail.svelte

@@ -62,7 +62,15 @@
 </nav>
 
 <style>
+  /* Self-assign the grid area so the parent App.svelte doesn't
+     need a `:global(nav.rail)` selector. Doing it via a parent
+     child-selector is fragile under Svelte 5's scoping — the
+     parent's `.shell.s-XXX > nav.rail` doesn't reliably match
+     `<nav class="rail s-YYY">` in the Tauri webview, which leaves
+     the buttons invisible to clicks. Owning the grid placement
+     here avoids the cross-component selector entirely. */
   .rail {
+    grid-area: rail;
     width: 88px;
     background: var(--bg);
     border-right: 1px solid var(--line);

crates/tauri-app/src/lib/components/PostCard.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+  import { untrack } from "svelte";
   import {
     fetchPost,
     likePost,
@@ -23,13 +24,24 @@
   let quotedErr: string | null = $state(null);
   let quotedLoading: boolean = $state(false);
 
+  // Resolve the embedded `app.bsky.embed.record` (a quoted post) by
+  // fetching the full record once per URI. We `untrack()` the
+  // in-flight check (`quoted` / `quotedLoading`) so a sync read+write
+  // of the same $state isn't reported as
+  // `effect_update_depth_exceeded` — without it, every time the
+  // effect re-fires (e.g. on parent re-render) Svelte 5's depth
+  // tracker saw `quotedLoading` read **and** flipped to `true`
+  // within the same tick.
   $effect(() => {
     const rec = (post.embed?.$type === "app.bsky.embed.record" || post.embed?.$type === "app.bsky.embed.recordWithMedia")
       ? post.embed?.record
       : null;
-    if (rec?.uri && !quoted && !quotedLoading) {
+    const targetUri = rec?.uri;
+    if (!targetUri) return;
+    untrack(() => {
+      if (quoted || quotedLoading) return;
       quotedLoading = true;
-      fetchPost(rec.uri)
+      fetchPost(targetUri)
         .then((r) => {
           quoted = r.post;
         })
@@ -39,7 +51,7 @@
         .finally(() => {
           quotedLoading = false;
         });
-    }
+    });
   });
 
   // Resolve the embed shape once at render time. We sniff $type to
@@ -99,13 +111,26 @@
     $state(null);
   $effect.pre(() => {
     const k = localStorageKey(`liked:${post.did}:${post.rkey}`);
-    likedBox = useLocalStorage<{ liked: boolean; uri: string | null }>(k, {
+    // Re-create the box whenever the post changes; the hydration
-      liked: false,
+    // reads (`likedBox.get()`) and the writes that seed `liked` /
-      uri: null,
+    // `likedUri` from localStorage all happen inside `untrack` so
+    // `likedBox` (which is $state) is **read and written in the same
+    // effect run**. Without untrack, Svelte 5's effect tracker would
+    // schedule `possible_effect_self_invalidation` on `likedBox`
+    // and the effect would loop until `effect_update_depth_exceeded`
+    // fires. See the explorer agent's read-out: this is THE loop
+    // that took down login with `process_fn x 95`. The outer
+    // `post.did` / `post.rkey` reads remain tracked so the effect
+    // still re-runs when navigating from one card to the next.
+    untrack(() => {
+      likedBox = useLocalStorage<{ liked: boolean; uri: string | null }>(k, {
+        liked: false,
+        uri: null,
+      });
+      const stored = likedBox.get();
+      liked = stored.liked;
+      likedUri = stored.uri;
     });
-    const stored = likedBox.get();
-    liked = stored.liked;
-    likedUri = stored.uri;
   });
   $effect(() => {
     if (!likedBox) return;

crates/tauri-app/src/lib/components/StatusBar.svelte

@@ -53,7 +53,11 @@
 </div>
 
 <style>
+  /* Self-assign the grid area — see NavRail.svelte for why we don't
+     rely on the parent's `:global(.statusbar)` child selector
+     (Svelte 5 scoping makes it unreliable in the Tauri webview). */
   .statusbar {
+    grid-area: status;
     height: 24px;
     background: var(--bg-elev);
     border-top: 1px solid var(--line);