From 439c09668ea7d5cf8804a4d20cd90a10055bf1ad Mon Sep 17 00:00:00 2001
From: Peter Steinberger <steipete@gmail.com>
Date: Sat, 30 May 2026 06:06:19 -0400
Subject: [PATCH] fix(ui): ignore invalid usage export timestamps

---
 ui/src/ui/views/usage-query.test.ts | 19 +++++++++++++++++++
 ui/src/ui/views/usage-query.ts      |  3 ++-
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 ui/src/ui/views/usage-query.test.ts

diff --git a/ui/src/ui/views/usage-query.test.ts b/ui/src/ui/views/usage-query.test.ts
new file mode 100644
index 00000000000..1c7197de771
--- /dev/null
+++ b/ui/src/ui/views/usage-query.test.ts
@@ -0,0 +1,19 @@
+// @vitest-environment node
+import { describe, expect, it } from "vitest";
+import { buildSessionsCsv } from "./usage-query.ts";
+import type { UsageSessionEntry } from "./usageTypes.ts";
+
+describe("usage query CSV export", () => {
+  it("omits invalid session updated timestamps instead of throwing", () => {
+    const csv = buildSessionsCsv([
+      {
+        key: "session-1",
+        label: "Session 1",
+        updatedAt: Number.POSITIVE_INFINITY,
+        usage: null,
+      } satisfies UsageSessionEntry,
+    ]);
+
+    expect(csv).toContain("session-1,Session 1,,,,,,,,,,,,,,,");
+  });
+});
diff --git a/ui/src/ui/views/usage-query.ts b/ui/src/ui/views/usage-query.ts
index 1a3e9f97642..148e7114fe5 100644
--- a/ui/src/ui/views/usage-query.ts
+++ b/ui/src/ui/views/usage-query.ts
@@ -1,3 +1,4 @@
+import { timestampMsToIsoString } from "../../../../src/shared/number-coercion.js";
 import { normalizeLowercaseStringOrEmpty, uniqueStrings } from "../string-coerce.ts";
 import { extractQueryTerms } from "../usage-helpers.ts";
 import type { CostDailyEntry, UsageAggregates, UsageSessionEntry } from "./usageTypes.ts";
@@ -63,7 +64,7 @@ const buildSessionsCsv = (sessions: UsageSessionEntry[]): string => {
         session.channel ?? "",
         session.modelProvider ?? session.providerOverride ?? "",
         session.model ?? session.modelOverride ?? "",
-        session.updatedAt ? new Date(session.updatedAt).toISOString() : "",
+        timestampMsToIsoString(session.updatedAt) ?? "",
         usage?.durationMs ?? "",
         usage?.messageCounts?.total ?? "",
         usage?.messageCounts?.errors ?? "",