feat(web): surface Discover freshness ("last discovered N ago") + true in-progress

/discover felt "stale until I hit Discover now": it showed the result string but
never WHEN the sweep last ran, and "Discovering…" ended the moment the worker
claimed the request (requested→false) rather than when the sweep finished.

- /api/discover/run GET now also returns `inProgress` (discover.inProgress) and
  `lastRunAt` (the discover.result Config row's updatedAt = last completion).
- The client treats requested||inProgress as "running", so "Discovering…"
  persists for the whole sweep, and polls until both clear before refreshing.
- The tool row shows "Last discovered {N ago} · {result}", a sweeping message
  while running, and a clear "Not yet run" empty state.

web 151 tests (inProgress + lastRunAt asserted), tsc + build clean. No worker
change (signals already written); NOT a page cache (would worsen staleness).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/api/discover/run/route.test.ts

@@ -12,10 +12,20 @@ describe("discover run API", () => {
     const body = await (await GET()).json();
     expect(body.requested).toBe(true);
     expect(body.result).toBeNull();
+    expect(body.inProgress).toBe(false);
+    expect(body.lastRunAt).toBeNull();
   });
 
-  it("GET returns discover.result when the worker has written it", async () => {
+  it("GET returns discover.result + lastRunAt when the worker has written it", async () => {
     await prisma.config.create({ data: { key: "discover.result", value: "artists 3, albums 1" } });
-    expect((await (await GET()).json()).result).toBe("artists 3, albums 1");
+    const body = await (await GET()).json();
+    expect(body.result).toBe("artists 3, albums 1");
+    expect(body.lastRunAt).not.toBeNull();
+    expect(Number.isNaN(Date.parse(body.lastRunAt))).toBe(false); // a real ISO timestamp
+  });
+
+  it("GET reports inProgress from discover.inProgress", async () => {
+    await prisma.config.create({ data: { key: "discover.inProgress", value: "true" } });
+    expect((await (await GET()).json()).inProgress).toBe(true);
   });
 });

web/src/app/api/discover/run/route.ts

@@ -10,12 +10,19 @@ export async function POST(_request: Request) {
 }
 
 export async function GET() {
-  const [requested, result] = await Promise.all([
+  const [requested, inProgress, result] = await Promise.all([
     prisma.config.findUnique({ where: { key: "discover.requested" } }),
+    prisma.config.findUnique({ where: { key: "discover.inProgress" } }),
     prisma.config.findUnique({ where: { key: "discover.result" } }),
   ]);
   return Response.json({
+    // a sweep is either queued (requested) or actively running (inProgress) — the UI treats
+    // both as "running" so "Discovering…" persists for the whole sweep, not just until the
+    // worker claims the request.
     requested: requested?.value === "true",
+    inProgress: inProgress?.value === "true",
     result: result?.value ?? null,
+    // when the last completed sweep wrote its result — the "last discovered N ago" signal.
+    lastRunAt: result?.updatedAt?.toISOString() ?? null,
   });
 }

web/src/app/discover/discover-client.tsx

@@ -2,6 +2,7 @@
 
 import { useCallback, useEffect, useState } from "react";
 import { PageHead } from "../_ui/page-head";
+import { timeAgo } from "../_ui/status";
 import { SectionHeader } from "../_ui/section-header";
 import { ArtistModal } from "../_ui/artist-modal";
 import { AlbumModal } from "../_ui/album-modal";
@@ -19,6 +20,12 @@ type Suggestion = {
   sources: string[];
 };
 
+/** "just now" / "3h ago" / "2d ago" — timeAgo has no suffix, so add one (except "just now"). */
+function agoLabel(value: string): string {
+  const a = timeAgo(value, Date.now());
+  return !a || a === "just now" ? a || "recently" : `${a} ago`;
+}
+
 type Feed = { artists: Suggestion[]; albums: Suggestion[] };
 type SearchResult = {
   seed: { mbid: string; name: string } | null;
@@ -28,6 +35,7 @@ type SearchResult = {
 export function DiscoverClient() {
   const [feed, setFeed] = useState<Feed>({ artists: [], albums: [] });
   const [result, setResult] = useState<string | null>(null);
+  const [lastRunAt, setLastRunAt] = useState<string | null>(null);
   const [running, setRunning] = useState(false);
   const [query, setQuery] = useState("");
   const [search, setSearch] = useState<SearchResult | null>(null);
@@ -44,9 +52,10 @@ export function DiscoverClient() {
     loadFeed();
     fetch("/api/discover/run")
       .then((r) => r.json())
-      .then((s: { result: string | null; requested: boolean }) => {
+      .then((s: { result: string | null; requested: boolean; inProgress: boolean; lastRunAt: string | null }) => {
         setResult(s.result);
-        setRunning(s.requested);
+        setLastRunAt(s.lastRunAt);
+        setRunning(s.requested || s.inProgress);
       });
   }, [loadFeed]);
 
@@ -55,7 +64,9 @@ export function DiscoverClient() {
     const id = setInterval(async () => {
       const s = await (await fetch("/api/discover/run")).json();
       setResult(s.result);
-      if (!s.requested) {
+      setLastRunAt(s.lastRunAt);
+      if (!s.requested && !s.inProgress) {
+        // the sweep finished (neither queued nor in progress) — refresh the feed
         setRunning(false);
         loadFeed();
       }
@@ -109,7 +120,13 @@ export function DiscoverClient() {
         <button className="btn accent" onClick={discoverNow} disabled={running}>
           {running ? "Discovering…" : "Discover now"}
         </button>
-        {result ? <span className="rmeta">last run · {result}</span> : null}
+        <span className="rmeta">
+          {running
+            ? "Sweeping your followed artists for new suggestions…"
+            : lastRunAt
+              ? `Last discovered ${agoLabel(lastRunAt)}${result ? ` · ${result}` : ""}`
+              : "Not yet run — press Discover now to sweep your followed artists"}
+        </span>
       </div>
 
       <SectionHeader title="Find similar" />