playground: stamp updatedb database with current time

Running the new locate/updatedb tests on real wasm surfaced a UX bug: updatedb
writes its database into the virtual filesystem with epoch (1970) timestamps,
so every subsequent locate warned "database is more than 8 days old (actual age
is 20626.6 days)". That warning also went to stderr, which the dispatcher merges
into the result and treats as pipeline-ending, breaking `locate ... | ...`.

Stamp the freshly-built database with "now" (same stat() patch used for the
sample files) so locate stays quiet and its stderr stays empty.

Author: sylvestre

static/js/wasm-terminal.js

@@ -524,6 +524,21 @@ function readVirtualFile(name) {
   return new TextDecoder().decode(file.data);
 }
 
+/**
+ * Stamp a virtual file's timestamps with "now". browser_wasi_shim creates
+ * files written by a WASM command (e.g. updatedb's database) with epoch (1970)
+ * timestamps; this patches stat() the same way getPersistentDir does for the
+ * sample files, so age-sensitive readers (locate) don't see a decades-old file.
+ */
+function touchVirtualFileNow(name) {
+  const dir = getPersistentDir();
+  const file = dir.dir.contents.get(resolvePath(name));
+  if (!file || typeof file.stat !== "function") return;
+  const nowNs = BigInt(Date.now()) * 1_000_000n;
+  const orig = file.stat.bind(file);
+  file.stat = () => { const s = orig(); s.atim = nowNs; s.mtim = nowNs; s.ctim = nowNs; return s; };
+}
+
 /**
  * Write a file to the virtual filesystem.
  */
@@ -727,6 +742,14 @@ async function executeCommandLine(line) {
       }
       const wasmArgs = isStandalone ? dispatchArgs : ["coreutils", ...resolvedArgs];
       const result = await runCommand(wasmArgs, stdinData, isStandalone ? standaloneModules[moduleName] : wasmModule);
+      // updatedb writes its database with epoch (1970) timestamps in the virtual
+      // FS, so a later `locate` would warn the db is decades old (and that stderr
+      // warning would break `locate … | …` pipes). Stamp the freshly-built db
+      // with "now" to keep locate quiet.
+      if (cmd === "updatedb" && result.exitCode === 0) {
+        const outArg = resolvedArgs.find(a => a.startsWith("--output="));
+        touchVirtualFileNow(outArg ? outArg.slice("--output=".length) : LOCATE_DB);
+      }
       if (result.stderr) {
         return result.stderr + result.stdout;
       }