fix(server): a directory no longer resolves as the resource monitor binary

apps/server/src/resourceTelemetry/ResourceMonitorBinary.test.ts

@@ -115,6 +115,28 @@ describe("ResourceMonitorBinary", () => {
     }).pipe(Effect.scoped, Effect.provide(NodeServices.layer)),
   );
 
+  it.effect("rejects a directory override", () =>
+    Effect.gen(function* () {
+      const fileSystem = yield* FileSystem.FileSystem;
+      const baseDir = yield* fileSystem.makeTempDirectoryScoped({
+        prefix: "t3-resource-monitor-binary-",
+      });
+
+      const service = yield* ResourceMonitorBinary.make().pipe(
+        Effect.provide(ServerConfig.layerTest(process.cwd(), baseDir)),
+        Effect.provideService(HostProcess.Platform, "win32"),
+        Effect.provideService(HostProcess.Architecture, "arm64"),
+        Effect.provideService(HostProcess.Environment, {
+          T3CODE_RESOURCE_MONITOR_PATH: baseDir,
+        }),
+      );
+      const error = yield* Effect.flip(service.resolve);
+
+      assert.instanceOf(error, ResourceMonitorBinary.ResourceMonitorBinaryNotExecutable);
+      assert.equal(error.path, baseDir);
+    }).pipe(Effect.scoped, Effect.provide(NodeServices.layer)),
+  );
+
   it.effect("rejects unsupported platform and architecture pairs", () =>
     Effect.gen(function* () {
       const fileSystem = yield* FileSystem.FileSystem;

apps/server/src/resourceTelemetry/ResourceMonitorBinary.ts

@@ -196,9 +196,14 @@ export const make = Effect.fn("resourceTelemetry.resourceMonitorBinary.make")(fu
       const exists = yield* fileSystem.exists(candidate).pipe(Effect.orElseSucceed(() => false));
       if (!exists) continue;
 
-      if (platform !== "win32") {
-        const stat = yield* fileSystem.stat(candidate).pipe(Effect.option);
-        if (Option.isSome(stat) && (stat.value.mode & 0o111) === 0) {
+      const stat = yield* fileSystem.stat(candidate).pipe(Effect.option);
+      if (Option.isSome(stat)) {
+        // Directories are executable-looking on win32, where the exec-bit test
+        // below is skipped, and only fail later at spawn.
+        const unusable =
+          stat.value.type === "Directory" ||
+          (platform !== "win32" && (stat.value.mode & 0o111) === 0);
+        if (unusable) {
           return yield* new ResourceMonitorBinaryNotExecutable({
             path: candidate,
             mode: stat.value.mode,