fix(dashboard): Round costs to two decimal places (#857)

Dashboard cost values now consistently render as USD with exactly two
decimal places across list rows, conversation details, charts, tooltips,
stats, and exports. The shared formatter test covers both sub-cent
values and rounding up to the next dollar.

Co-authored-by: GPT-5 Codex <noreply@openai.com>

Author: dcramer

packages/junior-dashboard/src/client/format.ts

@@ -533,7 +533,7 @@ export function summarizeCost(
   return total !== undefined || componentTotal > 0 ? summary : undefined;
 }
 
-/** Format estimated model cost in USD with useful sub-cent precision. */
+/** Format estimated model cost in USD for consistent dashboard display. */
 export function formatCostSummary(
   summary: CostUsageSummary | undefined,
 ): string {
@@ -542,7 +542,7 @@ export function formatCostSummary(
     style: "currency",
     currency: "USD",
     minimumFractionDigits: 2,
-    maximumFractionDigits: 6,
+    maximumFractionDigits: 2,
   }).format(summary.total);
 }
 

packages/junior-dashboard/tests/format.test.ts

@@ -82,7 +82,8 @@ describe("dashboard token formatting", () => {
       cacheWrite: undefined,
       total: 0.0121,
     });
-    expect(formatCostTotal(usage)).toBe("$0.0121");
+    expect(formatCostTotal(usage)).toBe("$0.01");
+    expect(formatCostTotal({ cost: { total: 1.999 } })).toBe("$2.00");
   });
 
   it("formats cumulative conversation runtime", () => {