Fix two intermittently failing library tests (closes #90)

Library.close() now returns a promise that resolves once the work it
started has finished: an in-flight refresh with its cache write, the ML
data fetch, and running precache sweeps. The interval test could see a
refresh's new state, close, and remove the directory while the write was
still running. Every library test and CLI command now awaits close(), and
tests hold each of the three writes open to prove close() waits for it.

The precache test waited for its stub source to be called, but the cache
records a file only after checking it on disk, so status() could lag. It
now waits for both fills to report "done".

Model: opus-5-5

src/library/index.ts

@@ -266,8 +266,9 @@ export class Library {
     // that, a fresh read propagates it.
     private cycle?: Promise<void>;
     // Guards the ML fetch pass so a slow backfill never runs twice at once; a
-    // refresh whose pass is still running kicks nothing new.
-    private mlFetching = false;
+    // refresh whose pass is still running kicks nothing new. Holds the running
+    // pass, so `close()` can wait for it.
+    private mlFetch?: Promise<void>;
     private closed = false;
     private lastRefreshAt?: number;
     private lastError?: string;
@@ -560,14 +561,21 @@ export class Library {
     }
 
     // Stop the background timer. Idempotent. An in-flight refresh is left to
-    // finish; it will not schedule another cycle once closed.
-    close(): void {
+    // finish; it will not schedule another cycle once closed. The returned
+    // promise resolves once that refresh (including its cache write), the ML
+    // fetch pass and the precache fetches already running have all finished,
+    // so a caller can then remove the cache directory. A refresh failure is
+    // reported through `status()`, not thrown here.
+    async close(): Promise<void> {
         this.closed = true;
-        this.precache?.close();
+        const precacheClosed = this.precache?.close();
         if (this.timer !== undefined) {
             clearTimeout(this.timer);
             this.timer = undefined;
         }
+        await this.cycle?.catch(() => {});
+        await this.mlFetch;
+        await precacheClosed;
     }
 
     private scheduleNext(): void {
@@ -631,7 +639,9 @@ export class Library {
             // outside the refresh's success/failure so a fetch or disk problem
             // there never marks the metadata refresh failed, and it is not
             // awaited so it never stalls the refresh interval.
-            void this.runMLFetch();
+            this.mlFetch ??= this.runMLFetch().finally(() => {
+                this.mlFetch = undefined;
+            });
         } catch (err) {
             const error = err instanceof Error ? err.message : String(err);
             this.lastError = error;
@@ -745,13 +755,12 @@ export class Library {
         // Bind so the call keeps the client as its receiver when invoked
         // through the pool below.
         const fetchMLData = this.client.fetchMLData?.bind(this.client);
-        if (!mldata || !fetchMLData || this.closed || this.mlFetching) return;
+        if (!mldata || !fetchMLData || this.closed) return;
 
         const files = this.uniqueFiles();
         const needed = mldata.neededFor(files);
         if (needed.length === 0) return;
 
-        this.mlFetching = true;
         this.emit({ operation: "fetchMLData", status: "started" });
         try {
             const fileKeys = new Map<number, Uint8Array>();
@@ -784,8 +793,6 @@ export class Library {
             const error = err instanceof Error ? err.message : String(err);
             this.lastMLError = error;
             this.emit({ operation: "fetchMLData", status: "failed", error });
-        } finally {
-            this.mlFetching = false;
         }
     }
 

src/library/precache.ts

@@ -92,9 +92,10 @@ export class Precache {
     private pinned = new Set<number>();
 
     // A sweep runs at most once per fill at a time; a re-kick while one runs is
-    // a no-op, and the next refresh re-kicks after it finishes.
-    private thumbRunning = false;
-    private originalsRunning = false;
+    // a no-op, and the next refresh re-kicks after it finishes. Each holds the
+    // running sweep, so `close()` can wait for it.
+    private thumbSweep?: Promise<void>;
+    private originalsSweep?: Promise<void>;
     private readonly aborter = new AbortController();
     private closed = false;
 
@@ -191,15 +192,19 @@ export class Precache {
     }
 
     // Stop the fills. In-flight fetches are left to settle; queued ones drop.
-    close(): void {
+    // Resolves once both sweeps have finished, so nothing is still writing.
+    async close(): Promise<void> {
         this.closed = true;
         this.aborter.abort();
+        await Promise.all([
+            this.thumbSweep?.catch(() => {}),
+            this.originalsSweep?.catch(() => {}),
+        ]);
     }
 
     private kickThumbnails(): void {
-        if (this.thumbRunning) return;
-        this.thumbRunning = true;
-        void this.sweep(
+        if (this.thumbSweep) return;
+        this.thumbSweep = this.sweep(
             "precacheThumbnails",
             () => this.thumbOrder,
             (id) => this.cache!.pathsFor(id).thumbnailPath !== undefined,
@@ -211,14 +216,13 @@ export class Precache {
                     signal: this.aborter.signal,
                 }),
         ).finally(() => {
-            this.thumbRunning = false;
+            this.thumbSweep = undefined;
         });
     }
 
     private kickOriginals(): void {
-        if (this.originalsRunning) return;
-        this.originalsRunning = true;
-        void this.sweep(
+        if (this.originalsSweep) return;
+        this.originalsSweep = this.sweep(
             "precacheOriginals",
             () => this.originalsOrder,
             (id) => this.cache!.pathsFor(id).originalPath !== undefined,
@@ -229,7 +233,7 @@ export class Precache {
                     signal: this.aborter.signal,
                 }),
         ).finally(() => {
-            this.originalsRunning = false;
+            this.originalsSweep = undefined;
         });
     }