fix: preserve exact beam pattern work caps

packages/acoustics-core/beam-pattern.js

@@ -368,9 +368,8 @@ export function computeReceiveBeamPattern(options) {
   }
   const preliminarySampleCount =
     requestedSampleCount === "auto" ? 36 : requestedSampleCount;
-  const preliminaryMaximumEvaluationCount = microphoneCount * (
-    preliminarySampleCount + HPBW_BISECTION_ITERATIONS * 2
-  );
+  const preliminaryMaximumEvaluationCount =
+    microphoneCount * preliminarySampleCount;
   if (
     !Number.isSafeInteger(preliminaryMaximumEvaluationCount) ||
     preliminaryMaximumEvaluationCount > maximumEvaluations

tests/unit/beam-pattern.test.js

@@ -389,3 +389,27 @@ test("beam-pattern preflight rejects invalid input and excessive work", () => {
   assert(frequencyLimitError instanceof RangeError, "extreme analog frequency is bounded");
   assert(frequencyLimitError.message.includes("1000000"), "frequency cap is explicit");
 });
+
+test("co-located pattern accepts an exact sample-only evaluation cap", () => {
+  const pattern = computeReceiveBeamPattern({
+    array: arrayFromPositions([[0, 0, 0]]),
+    frequencyHz: 1_000,
+    sampleCount: 360,
+    maximumEvaluations: 360,
+  });
+  assertEqual(pattern.evaluationCount, 360, "exact one-microphone sample work");
+  assertEqual(pattern.workload.maximumMetricEvaluationCount, 0, "constant cut reserves no HPBW work");
+
+  let error = null;
+  try {
+    computeReceiveBeamPattern({
+      array: arrayFromPositions([[0, 0, 0]]),
+      frequencyHz: 1_000,
+      sampleCount: 360,
+      maximumEvaluations: 359,
+    });
+  } catch (caught) {
+    error = caught;
+  }
+  assert(error instanceof RangeError, "strict cap rejects one fewer evaluation");
+});