diff --git a/src/domain/analysisView/environmentStateRules.ts b/src/domain/analysisView/environmentStateRules.ts
index d8f0644f77..d029ff9d25 100644
--- a/src/domain/analysisView/environmentStateRules.ts
+++ b/src/domain/analysisView/environmentStateRules.ts
@@ -398,11 +398,14 @@ export const identifies = (
   items: readonly JsonObject[],
   name: string,
 ): boolean => {
-  const values = items.map((item) => scalarText(item[name]));
-  return (
-    values.every((value) => value !== undefined) &&
-    new Set(values).size === values.length
-  );
+  // Stop at the first missing or repeated value, so a sparse list costs one read per field.
+  const seen = new Set<string>();
+  for (const item of items) {
+    const value = scalarText(item[name]);
+    if (value === undefined || seen.has(value)) return false;
+    seen.add(value);
+  }
+  return true;
 };
 
 /** Fields ending in one of these may identify listed items that no identity name identifies. */
diff --git a/src/domain/analysisView/environmentStateView.test.ts b/src/domain/analysisView/environmentStateView.test.ts
index 58cca153b9..cd5eb2b39f 100644
--- a/src/domain/analysisView/environmentStateView.test.ts
+++ b/src/domain/analysisView/environmentStateView.test.ts
@@ -17,7 +17,12 @@ import {
   type AnalysisViewResult,
 } from "./analysisView.js";
 import { EnvironmentStateAccumulator } from "./EnvironmentStateAccumulator.js";
-import { at, replaceAt } from "./environmentStateRules.js";
+import {
+  at,
+  identityCandidates,
+  replaceAt,
+  type JsonObject,
+} from "./environmentStateRules.js";
 
 type State = Extract<AnalysisViewResult, { kind: "environment-state" }>;
 const ALL_RULES = [
@@ -1007,3 +1012,30 @@ it("reads only item totals and next-page markers as signs of a partial list", ()
     ["recorded", []],
   ]);
 });
+
+it("reads a sparse list once per candidate field when inferring identity", () => {
+  const fields = 2_000;
+  const wide: JsonObject = Object.fromEntries(
+    Array.from({ length: fields }, (_, index) => [
+      `f${String(index)}Id`,
+      index,
+    ]),
+  );
+  let reads = 0;
+  const sparse = Array.from(
+    { length: 5_000 },
+    () =>
+      new Proxy<JsonObject>(
+        {},
+        {
+          get: (target, key, receiver) => {
+            reads += 1;
+            return Reflect.get(target, key, receiver) as unknown;
+          },
+        },
+      ),
+  );
+  expect(identityCandidates([wide, ...sparse])).toEqual([]);
+  // Each identity name and suffix field stops at the first sparse item.
+  expect(reads).toBeLessThanOrEqual(fields + 20);
+});