test: add dashboard formatter time axis tests for multi-day spans

Add tests that exercise the MM/DD (2-30 day) and Mon DD (>30 day) branches
of the formatTimestamp function in the dashboard formatter. These branches
are only reached via renderTimeseriesBarsContent (contentHeight >= 8),
which requires layout.h >= 2 so the widget box is tall enough.

Author: BYK

test/lib/formatters/dashboard.test.ts

@@ -1515,3 +1515,69 @@ describe("createDashboardViewRenderer", () => {
     });
   });
 });
+
+// ===========================================================================
+// formatTimestamp branch coverage
+// Tests for the three branches in formatTimestamp (internal helper):
+// - < 2 days: HH:MM
+// - 2-30 days: MM/DD
+// - > 30 days: Mon DD
+// These are exercised by formatting dashboards with appropriate time spans.
+// ===========================================================================
+
+describe("formatDashboardWithData — time axis formats", () => {
+  usePlainMode();
+
+  /**
+   * Create a time series spanning the given number of days, centered around
+   * 2024-01-15. Returns a TimeseriesResult whose timestamps span enough range
+   * to trigger the right formatTimestamp branch.
+   */
+  function makeSpannedTimeseries(days: number): TimeseriesResult {
+    const now = new Date("2024-01-15T12:00:00Z").getTime() / 1000;
+    const start = now - days * 24 * 3600;
+    const numPoints = 5;
+    const step = (days * 24 * 3600) / numPoints;
+    const values = Array.from({ length: numPoints + 1 }, (_, i) => ({
+      timestamp: start + i * step,
+      value: Math.floor(Math.random() * 100),
+    }));
+    return {
+      type: "timeseries",
+      series: [{ label: "count()", values }],
+    };
+  }
+
+  test("renders time axis with MM/DD format for 7-day span", () => {
+    const data = makeDashboardData({
+      period: "7d",
+      widgets: [
+        // layout.h=2 → totalHeight=12, contentHeight=10 >= 8 → renderTimeseriesBarsContent
+        makeWidget({
+          displayType: "line",
+          layout: { x: 0, y: 0, w: 6, h: 2 },
+          data: makeSpannedTimeseries(7),
+        }),
+      ],
+    });
+    const output = formatDashboardWithData(data);
+    // 7-day span → MM/DD format like "01/15"
+    expect(output).toMatch(/\d{2}\/\d{2}/);
+  });
+
+  test("renders time axis with Mon DD format for 90-day span", () => {
+    const data = makeDashboardData({
+      period: "90d",
+      widgets: [
+        makeWidget({
+          displayType: "line",
+          layout: { x: 0, y: 0, w: 6, h: 2 },
+          data: makeSpannedTimeseries(90),
+        }),
+      ],
+    });
+    const output = formatDashboardWithData(data);
+    // 90-day span → "Jan 15" style format
+    expect(output).toMatch(/Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec/);
+  });
+});