android: what the phone says when things go wrong

Fifty-nine places put a raw Rust string into a field a person reads, and
the red toast drew it verbatim — a phone in a lift showed "could not reach
server: io: failed to lookup address information" under the password box.
One translator, src/mobile/trouble.js, called where an error is DRAWN
rather than where it is caught: the stores keep what Rust said and only
the sentence on screen is ours, so every sink is fixed at once. Five
screens that drew a failed read as an empty answer stop lying — Tracks no
longer reports a broken database as an empty library, a playlist that
could not be read is not an empty playlist, the lyrics face says a lookup
failed instead of "no lyrics" and finally carries the ⋯ that reaches Paste
lyrics, Gaps says why it could not reach the catalogue, and Search signed
out says so where it used to render nothing at all. The room list, which
is fire-and-forget over the wire, gets a twelve-second end and a Try
again.

rescan_library ran prune_missing() first, which deletes every track row
whose file does not exist — so one tap on You → Rescan library with the
folder unreachable emptied the whole index and returned Ok(()). It now
makes the root if it is merely not there yet and refuses if it cannot be
read, and You draws the path with what to do about it.

The mock grew a weather system so the walk can drive all of this: fail,
answer, offline and clear, checked before dispatch so a plugin command
arms like any other. Nine mock steps and one on the phone — the first
steps in thirty rounds that ever made a command reject or saw the client
signed out — and the last of them puts the weather away and leaves the app
as it found it.

src/mobile/screens/Library.svelte

@@ -62,6 +62,9 @@
     let gapRows = $state({});      // foldKey(artist) → catalog rows not owned
     let gapOpen = $state({});
     let gapLoading = $state({});
+    /* the lookup's catch was empty, so a failed reach put the line back to
+       "See what's missing" and it could be tapped for ever with no reason */
+    let gapErr = $state({});
     const shelves = $derived(arts.filter((ar) => followedEntry(ar.name)));
     const ownedTitles = (name) => new Set(lib.albums.filter((a) => foldKey(a.artist) === foldKey(name)).map((a) => looseTitle(a.title)));
     async function toggleGaps(name) {
@@ -71,6 +74,7 @@
         if (!follow) return;
         if (!gapRows[key] && !gapLoading[key]) {
             gapLoading = { ...gapLoading, [key]: true };
+            gapErr = { ...gapErr, [key]: "" };
             try {
                 const page = await api.catalogArtist(follow.artist_id);
                 const released = (page?.albums ?? []).filter((a) => !isUpcoming(a) && !a.appears_on);
@@ -78,7 +82,7 @@
                 gapRows = { ...gapRows, [key]: released.filter((r) => !owned.has(looseTitle(r.title))) };
                 gapTotals = { ...gapTotals, [key]: { total: released.length } };
                 try { localStorage.setItem(GAPS_KEY, JSON.stringify(gapTotals)); } catch { /* ignore */ }
-            } catch { /* the line stays collapsed; nothing is invented */ }
+            } catch (e) { gapErr = { ...gapErr, [key]: String(e) }; }
             gapLoading = { ...gapLoading, [key]: false };
         }
         if (gapRows[key]) gapOpen = { ...gapOpen, [key]: true };
@@ -171,7 +175,7 @@
             </button>
             {#if count !== 0}
                 <button class="gapline" onclick={() => toggleGaps(ar.name)} aria-expanded={!!gapOpen[key]}>
-                    {#if gapLoading[key]}Checking the catalogue…{:else if count != null}<b>{count}</b> more released{:else}See what's missing{/if}
+                    {#if gapLoading[key]}Checking the catalogue…{:else if gapErr[key]}Couldn't reach the catalogue — tap to try again{:else if count != null}<b>{count}</b> more released{:else}See what's missing{/if}
                     <span class="cta">{gapOpen[key] ? "hide" : "show"}<Icon name={gapOpen[key] ? "chevron-down" : "chevron-right"} size={12} /></span>
                 </button>
             {:else}