fix regression in derive dependency handling

bau/bau.js

@@ -301,14 +301,9 @@ export default function Bau(input) {
     state.val = runAndCaptureDeps(computed, deps);
 
     let listener = { computed, state };
-    for (let dep of new Set(
-      [...deps.g].filter(
-        (dep) =>
-          !deps.s.has(dep) &&
-          dep.listeners.every((listener) => !deps.g.has(listener.state))
-      )
-    ))
-      dep.listeners.push(listener);
+    for (let dep of new Set([...deps.g].filter((dep) => !deps.s.has(dep)))) {
+      if (!dep.listeners.some((l) => l.state === state)) dep.listeners.push(listener);
+    }
     state.dirty = false;
   };
 

bau/test/derive.test.js

@@ -162,4 +162,25 @@ describe("derive", async () => {
     assert.equal(derived.val, 1);
     assert.equal(called, 2);
   });
+
+  it("does not recompute more than once per update", async () => {
+    const a = bau.state(0);
+    let called = 0;
+    const d = bau.derive(() => {
+      called++;
+      return a.val + 1;
+    });
+    // Initial compute
+    assert.strictEqual(d.val, 1);
+    assert.strictEqual(called, 1);
+    // Drive several recomputations to simulate potential duplicate subscriptions
+    a.val = 2; await sleep();
+    a.val = 3; await sleep();
+    a.val = 4; await sleep();
+    const before = called;
+    // A single update should trigger exactly one recompute
+    a.val = 5; await sleep();
+    assert.strictEqual(called - before, 1);
+    assert.strictEqual(d.val, 6);
+  });
 });