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frontend/test-support/file-application.test.ts

@@ -89,6 +89,49 @@ test("content edited after planning is merged with the incoming snapshot", async
     );
 });
 
+test("repeated large text replacements reuse WebAssembly memory", async () => {
+    // The replacement from fuzz-193329 exhausted reconcile-text 0.8.0's
+    // allocator over repeated merges, eventually stalling sync and trapping.
+    const original = (
+        " مرحباéשלום\t日本語\ncaféalphaalphaनमस्ते🦊🌍café\n" +
+        "🌍مرحبامرحباनमस्तेשלום\talphaalphacaféمرحبا🌍\r\n日本語مرحبا"
+    ).repeat(128);
+    const replacement = await hashSnapshot({
+        content: bytes(
+            (
+                "alpha🌍éनमस्ते日本語שלום\uFEFFשלום\t\r\n" +
+                "\uFEFF🦊 🦊🌍नमस्ते\uFEFFéمرحبا\r\ncafé🌍é🌍"
+            ).repeat(128)
+        )
+    });
+    const f = await fixture({ "a.md": original });
+    const expected = (await f.files.readSnapshot("a.md"))!;
+    const apply = async () => {
+        await f.disk.userWrite("a.md", bytes(original));
+        await f.files.applyChanges(structuredClone(f.database.state), {
+            a: { expected, replacement }
+        });
+        assert.deepEqual(f.disk.userFiles().get("a.md"), replacement.content);
+        assert.equal(
+            f.database.state.documents.a.observedHash,
+            replacement.hash
+        );
+    };
+
+    await apply(); // Warm up the module and its allocator before measuring.
+    const warmedMemory = process.memoryUsage.rss();
+    for (let repeat = 0; repeat < 4; repeat++) {
+        await apply();
+        // Measure resident memory because V8's external counter can omit WASM
+        // memory after GC. The old allocator grew ~150 MiB on every call.
+        const growth = process.memoryUsage.rss() - warmedMemory;
+        assert(
+            growth < 64 * 1024 * 1024,
+            `Resident memory grew by ${growth} bytes`
+        );
+    }
+});
+
 test("deleting the source after planning does not resurrect it", async () => {
     const f = await fixture();
     const next = structuredClone(f.database.state);