feat(tooltip): preserve fractional precision in used / overage values

Mirror upstream chatStatusDashboard's quotaCreditsFormatter so a float
like 195.9 stays 195.9 instead of being rounded to 196. The fallback
percent-based used calc no longer pre-rounds; the tooltip formats with
Intl.NumberFormat({ maximumFractionDigits: 2 }) at render time.

Author: euxx

CHANGELOG.md

@@ -11,7 +11,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - **Token-based billing (UBB) support**: auto-detects GitHub's new credit-based billing mode via the `token_based_billing` field. The tooltip title switches between **Copilot Premium Requests** (legacy) and **Copilot Credits** (UBB), so the count line stays a familiar `Used: 90 / 300 (30%)`. Overage line still labels its unit (`Overage: 5 requests` vs `Additional credits: 5`).
 - **`individual_max` (Max) and `individual_edu` (Student) plans** in the plan-name map.
 - **Per-snapshot `quota_reset_at`** (Unix seconds) read with top priority under UBB; falls back to `quota_reset_date_utc` then `quota_reset_date`. Shared by all return paths so pooled-exhausted users still see real reset times.
-- **Precise `used` calculation** via `quota_remaining` when present (avoids float precision loss from percentage-based reverse calculation).
+- **Precise `used` calculation** via `quota_remaining` when present (avoids float precision loss from percentage-based reverse calculation). Tooltip formats `used`, `quota`, and overage values with `Intl.NumberFormat({ maximumFractionDigits: 2 })` to preserve fractional precision (e.g. `195.9` instead of `196`), matching upstream's `quotaCreditsFormatter`.
 - **Pooled entitlement exhaustion**: enterprise unlimited plans signaling `has_quota=false` (without overage) now display `100%` red instead of misleadingly showing `∞`. Tooltip surfaces "Quota: Unlimited · pool exhausted" with the reset date.
 
 ### Changed

src/api.js

@@ -140,7 +140,7 @@ async function fetchUsage(token) {
       quotaRemaining !== undefined
         ? Math.max(0, entitlement - quotaRemaining)
         : entitlement > 0
-          ? Math.max(0, Math.round((entitlement * (100 - percentRemaining)) / 100))
+          ? Math.max(0, (entitlement * (100 - percentRemaining)) / 100)
           : 0;
 
     return { ...shared, used, usedPct, noData: false };

src/extension.js

@@ -180,6 +180,16 @@ function computeDisplayPct(data) {
 
 const BILLING_URL = "https://github.com/settings/billing/premium_requests_usage";
 
+// Mirrors vscode's quotaCreditsFormatter (chatStatusDashboard.ts): keep up to 2 fractional
+// digits so a float like 195.9 stays 195.9 instead of being rounded to 196 here.
+// Upstream also has a compact formatter for >= 100k; we skip that — premium quotas don't
+// reach that magnitude in practice, and the credit dashboard handles compact rendering
+// in its own surface.
+const usageFormatter = new Intl.NumberFormat(undefined, {
+  maximumFractionDigits: 2,
+  minimumFractionDigits: 0,
+});
+
 /**
  * @param {import('./api').UsageData} data
  * @param {boolean} [isRateLimited]
@@ -295,12 +305,12 @@ function buildTooltip(data, isRateLimited, isOfflineState = false, isStale = fal
     // Title already names the unit (Credits vs Premium requests), so the
     // count line uses a neutral "Used:" label and skips the unit suffix.
     md.appendMarkdown(
-      `Used: ${data.used} / ${data.quota} (${data.usedPct}%)  [$(graph)](${BILLING_URL})\n\n`,
+      `Used: ${usageFormatter.format(data.used)} / ${usageFormatter.format(data.quota)} (${data.usedPct}%)  [$(graph)](${BILLING_URL})\n\n`,
     );
     if (data.overageEnabled && data.overageUsed > 0) {
       const overageLine = data.tokenBasedBilling
-        ? `Additional credits: ${data.overageUsed}`
-        : `Overage: ${data.overageUsed} requests`;
+        ? `Additional credits: ${usageFormatter.format(data.overageUsed)}`
+        : `Overage: ${usageFormatter.format(data.overageUsed)} requests`;
       md.appendMarkdown(`${overageLine}\n\n`);
     }
     appendResetLine(md, data.resetDate);

tests/api.test.js

@@ -40,7 +40,7 @@ describe("fetchUsage", () => {
       const data = await fetchUsage("test-token");
       expect(data.plan).toBe("Pro");
       expect(data.usedPct).toBe(30); // 100 - 70
-      expect(data.used).toBe(90); // round(300 * 30 / 100)
+      expect(data.used).toBe(90); // 300 * 30 / 100
       expect(data.quota).toBe(300);
       expect(data.unlimited).toBe(false);
       expect(data.noData).toBe(false);
@@ -239,9 +239,29 @@ describe("fetchUsage", () => {
       };
       fetch.mockResolvedValue(mockRes(200, body));
       const data = await fetchUsage("test-token");
-      // entitlement=300, percent_remaining=70 → used = round(300 * 30 / 100) = 90
+      // entitlement=300, percent_remaining=70 → used = 300 * 30 / 100 = 90
       expect(data.used).toBe(90);
     });
+
+    it("preserves fractional precision in `used` (matches vscode dashboard)", async () => {
+      // Upstream chatStatusDashboard stores `used` as a float and formats with
+      // Intl.NumberFormat({ maximumFractionDigits: 2 }) at render time. We mirror
+      // that by not pre-rounding here. Concrete case: entitlement=300, percent_remaining=34.7
+      // → used = 300 * 65.3 / 100 = 195.9 (vscode shows 195.9, not 196).
+      const body = {
+        ...BASE_BODY,
+        quota_snapshots: {
+          premium_interactions: {
+            ...BASE_BODY.quota_snapshots.premium_interactions,
+            percent_remaining: 34.7,
+            quota_remaining: undefined,
+          },
+        },
+      };
+      fetch.mockResolvedValue(mockRes(200, body));
+      const data = await fetchUsage("test-token");
+      expect(data.used).toBeCloseTo(195.9, 5);
+    });
   });
 
   describe("plan mapping", () => {

tests/extension.test.js

@@ -124,6 +124,14 @@ describe("buildTooltip", () => {
     expect(md.value).toContain("Used: 90 / 300 (30%)");
   });
 
+  it("formats fractional `used` with up to 2 decimal places (matches vscode)", () => {
+    // Mirrors upstream Intl.NumberFormat({ maximumFractionDigits: 2 }) behavior:
+    // a float like 195.9 is preserved instead of being rounded to 196.
+    const data = { ...BASE_DATA, used: 195.9, usedPct: 65.3 };
+    const md = buildTooltip(data, false);
+    expect(md.value).toContain("Used: 195.9 / 300 (65.3%)");
+  });
+
   it("uses 'Copilot Premium Requests' title in legacy mode", () => {
     const md = buildTooltip(BASE_DATA, false);
     expect(md.value).toContain("**Copilot Premium Requests**");