diff --git a/src/gateway/server-methods/usage.test.ts b/src/gateway/server-methods/usage.test.ts
index 3a64a224c6d3..6ae9f307e983 100644
--- a/src/gateway/server-methods/usage.test.ts
+++ b/src/gateway/server-methods/usage.test.ts
@@ -37,6 +37,39 @@ import { testApi, usageHandlers } from "./usage.js";
 
 describe("gateway usage helpers", () => {
   const dayMs = 24 * 60 * 60 * 1000;
+  const costSummary = (params: { date?: string; totalTokens: number; totalCost: number }) => ({
+    updatedAt: Date.now(),
+    days: 1,
+    daily: [
+      {
+        date: params.date ?? "2026-02-01",
+        input: params.totalTokens,
+        output: 0,
+        cacheRead: 0,
+        cacheWrite: 0,
+        totalTokens: params.totalTokens,
+        totalCost: params.totalCost,
+        inputCost: params.totalCost,
+        outputCost: 0,
+        cacheReadCost: 0,
+        cacheWriteCost: 0,
+        missingCostEntries: 0,
+      },
+    ],
+    totals: {
+      input: params.totalTokens,
+      output: 0,
+      cacheRead: 0,
+      cacheWrite: 0,
+      totalTokens: params.totalTokens,
+      totalCost: params.totalCost,
+      inputCost: params.totalCost,
+      outputCost: 0,
+      cacheReadCost: 0,
+      cacheWriteCost: 0,
+      missingCostEntries: 0,
+    },
+  });
 
   function expectUtcDateRange(
     range: ReturnType<typeof testApi.parseDateRange>,
@@ -257,4 +290,64 @@ describe("gateway usage helpers", () => {
       expect.objectContaining({ agentId: "research" }),
     );
   });
+
+  it("aggregates usage.cost only for explicit all-agent scope", async () => {
+    vi.mocked(loadCostUsageSummaryFromCache).mockImplementation(async (params) =>
+      params?.agentId === "opus"
+        ? costSummary({ totalTokens: 20, totalCost: 2 })
+        : costSummary({ totalTokens: 10, totalCost: 1 }),
+    );
+
+    const config = {
+      agents: { list: [{ id: "main" }, { id: "opus" }] },
+      session: {},
+    } as OpenClawConfig;
+    const context = { getRuntimeConfig: () => config };
+    const params = { startDate: "2026-02-01", endDate: "2026-02-01", mode: "utc" };
+
+    const defaultRespond = vi.fn();
+    await usageHandlers["usage.cost"]({
+      respond: defaultRespond,
+      params,
+      context,
+    } as unknown as Parameters<(typeof usageHandlers)["usage.cost"]>[0]);
+
+    expect(vi.mocked(loadCostUsageSummaryFromCache)).toHaveBeenCalledTimes(1);
+    expect(vi.mocked(loadCostUsageSummaryFromCache).mock.calls[0]?.[0]?.agentId).toBeUndefined();
+    expect(defaultRespond.mock.calls[0]?.[1]).toMatchObject({
+      totals: { totalTokens: 10, totalCost: 1 },
+    });
+
+    const aggregateRespond = vi.fn();
+    await usageHandlers["usage.cost"]({
+      respond: aggregateRespond,
+      params: { ...params, agentScope: "all" },
+      context,
+    } as unknown as Parameters<(typeof usageHandlers)["usage.cost"]>[0]);
+
+    expect(vi.mocked(loadCostUsageSummaryFromCache)).toHaveBeenCalledTimes(3);
+    expect(
+      vi.mocked(loadCostUsageSummaryFromCache)
+        .mock.calls.slice(1)
+        .map((call) => call[0]?.agentId),
+    ).toEqual(["main", "opus"]);
+    expect(aggregateRespond.mock.calls[0]?.[0]).toBe(true);
+    expect(aggregateRespond.mock.calls[0]?.[1]).toMatchObject({
+      totals: { totalTokens: 30, totalCost: 3 },
+      daily: [{ date: "2026-02-01", totalTokens: 30, totalCost: 3 }],
+    });
+
+    const mainRespond = vi.fn();
+    await usageHandlers["usage.cost"]({
+      respond: mainRespond,
+      params: { ...params, agentId: "main" },
+      context,
+    } as unknown as Parameters<(typeof usageHandlers)["usage.cost"]>[0]);
+
+    expect(vi.mocked(loadCostUsageSummaryFromCache)).toHaveBeenCalledTimes(4);
+    expect(vi.mocked(loadCostUsageSummaryFromCache).mock.calls[3]?.[0]?.agentId).toBe("main");
+    expect(mainRespond.mock.calls[0]?.[1]).toMatchObject({
+      totals: { totalTokens: 10, totalCost: 1 },
+    });
+  });
 });
diff --git a/ui/src/ui/views/usage-metrics.node.test.ts b/ui/src/ui/views/usage-metrics.node.test.ts
new file mode 100644
index 000000000000..e5bd06a604aa
--- /dev/null
+++ b/ui/src/ui/views/usage-metrics.node.test.ts
@@ -0,0 +1,23 @@
+// @vitest-environment node
+import { describe, expect, it } from "vitest";
+import { withEnvAsync } from "../../../../src/test-utils/env.js";
+import { formatDayLabel, formatFullDate } from "./usage-metrics.ts";
+
+describe("usage metrics date labels", () => {
+  it("formats YYYY-MM-DD values as stable calendar dates in negative UTC offsets", async () => {
+    await withEnvAsync({ TZ: "America/Los_Angeles" }, async () => {
+      const date = new Date(2026, 1, 1);
+      expect(formatDayLabel("2026-02-01")).toBe(
+        date.toLocaleDateString(undefined, { month: "short", day: "numeric" }),
+      );
+      expect(formatFullDate("2026-02-01")).toBe(
+        date.toLocaleDateString(undefined, { month: "long", day: "numeric", year: "numeric" }),
+      );
+    });
+  });
+
+  it("leaves invalid day labels unchanged", () => {
+    expect(formatDayLabel("2026-02-31")).toBe("2026-02-31");
+    expect(formatFullDate("2026-02-31")).toBe("2026-02-31");
+  });
+});
diff --git a/ui/src/ui/views/usage-metrics.ts b/ui/src/ui/views/usage-metrics.ts
index eb077d6adde2..6618f046796a 100644
--- a/ui/src/ui/views/usage-metrics.ts
+++ b/ui/src/ui/views/usage-metrics.ts
@@ -452,8 +452,19 @@ function parseYmdDate(dateStr: string): Date | null {
     return null;
   }
   const [, y, m, d] = match;
-  const date = new Date(Date.UTC(Number(y), Number(m) - 1, Number(d)));
-  return Number.isNaN(date.valueOf()) ? null : date;
+  const year = Number(y);
+  const monthIndex = Number(m) - 1;
+  const day = Number(d);
+  const date = new Date(year, monthIndex, day);
+  if (
+    Number.isNaN(date.valueOf()) ||
+    date.getFullYear() !== year ||
+    date.getMonth() !== monthIndex ||
+    date.getDate() !== day
+  ) {
+    return null;
+  }
+  return date;
 }
 
 function formatDayLabel(dateStr: string): string {