feat: compact usage widget in authenticated layout header

apps/web/src/components/layout/AppHeader.tsx

@@ -5,6 +5,7 @@ import Link from "next/link";
 import { usePathname } from "next/navigation";
 import { useAuth } from "@/lib/auth/auth-context";
 import { ThemeToggle } from "./ThemeToggle";
+import { UsageWidget } from "@/components/ui/UsageWidget";
 import { useSidebar } from "./SidebarContext";
 
 /**
@@ -350,6 +351,9 @@ export function AppHeader(): React.JSX.Element {
         {/* Theme Toggle */}
         <ThemeToggle />
 
+        {/* Usage Widget */}
+        <UsageWidget />
+
         {/* User Avatar + Dropdown */}
         <div ref={dropdownRef} style={{ position: "relative", flexShrink: 0 }}>
           <button

apps/web/src/components/ui/UsageWidget.tsx

@@ -0,0 +1,337 @@
+"use client";
+
+import { useState, useEffect, useRef, useCallback } from "react";
+import { fetchUsageSummary, type UsageSummary } from "@/lib/api/telemetry";
+
+// ─── Types ───────────────────────────────────────────────────────────
+
+interface UsageTier {
+  name: string;
+  tokens: number;
+  limit: number;
+  percentage: number;
+}
+
+// ─── Helpers ─────────────────────────────────────────────────────────
+
+function getUsageColor(percentage: number): string {
+  if (percentage < 60) return "var(--success)";
+  if (percentage < 80) return "var(--warn)";
+  return "var(--danger)";
+}
+
+function formatTokens(value: number): string {
+  if (value >= 1_000_000) return `${(value / 1_000_000).toFixed(1)}M`;
+  if (value >= 1_000) return `${(value / 1_000).toFixed(1)}K`;
+  return value.toFixed(0);
+}
+
+// ─── Component ───────────────────────────────────────────────────────
+
+export function UsageWidget(): React.JSX.Element {
+  const [summary, setSummary] = useState<UsageSummary | null>(null);
+  const [popoverOpen, setPopoverOpen] = useState(false);
+  const [isLoading, setIsLoading] = useState(true);
+  const popoverRef = useRef<HTMLDivElement>(null);
+
+  const tiers: UsageTier[] = summary
+    ? [
+        {
+          name: "Session",
+          tokens: summary.totalTokens,
+          limit: 100_000,
+          percentage: (summary.totalTokens / 100_000) * 100,
+        },
+        {
+          name: "Daily",
+          tokens: summary.totalTokens,
+          limit: 500_000,
+          percentage: (summary.totalTokens / 500_000) * 100,
+        },
+        {
+          name: "Monthly",
+          tokens: summary.totalTokens,
+          limit: 2_000_000,
+          percentage: (summary.totalTokens / 2_000_000) * 100,
+        },
+      ]
+    : [];
+
+  const currentTier = tiers[0];
+  const usageColor = currentTier ? getUsageColor(currentTier.percentage) : "var(--muted)";
+
+  const loadSummary = useCallback(async () => {
+    try {
+      const data = await fetchUsageSummary("30d");
+      setSummary(data);
+    } catch (err) {
+      console.error("Failed to load usage summary:", err);
+    } finally {
+      setIsLoading(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    void loadSummary();
+  }, [loadSummary]);
+
+  useEffect(() => {
+    function handleClickOutside(event: MouseEvent): void {
+      if (popoverRef.current && !popoverRef.current.contains(event.target as Node)) {
+        setPopoverOpen(false);
+      }
+    }
+
+    if (!popoverOpen) {
+      return;
+    }
+
+    document.addEventListener("mousedown", handleClickOutside);
+    return (): void => {
+      document.removeEventListener("mousedown", handleClickOutside);
+    };
+  }, [popoverOpen]);
+
+  const pct = currentTier ? Math.min(currentTier.percentage, 100) : 0;
+
+  return (
+    <div ref={popoverRef} style={{ position: "relative" }}>
+      <button
+        onClick={(): void => {
+          setPopoverOpen((prev) => !prev);
+        }}
+        aria-label="Usage widget"
+        aria-expanded={popoverOpen}
+        aria-haspopup="true"
+        className="hidden lg:flex items-center"
+        style={{
+          gap: 6,
+          padding: "5px 10px",
+          borderRadius: 6,
+          background: "var(--surface)",
+          border: `1px solid ${popoverOpen ? usageColor : "var(--border)"}`,
+          fontSize: "0.75rem",
+          fontFamily: "var(--mono)",
+          color: "var(--text-2)",
+          cursor: "pointer",
+          transition: "border-color 0.15s, color 0.15s",
+          flexShrink: 0,
+        }}
+        onMouseEnter={(e): void => {
+          (e.currentTarget as HTMLButtonElement).style.borderColor = usageColor;
+          (e.currentTarget as HTMLButtonElement).style.color = "var(--text)";
+        }}
+        onMouseLeave={(e): void => {
+          if (!popoverOpen) {
+            (e.currentTarget as HTMLButtonElement).style.borderColor = "var(--border)";
+            (e.currentTarget as HTMLButtonElement).style.color = "var(--text-2)";
+          }
+        }}
+      >
+        <svg
+          width="12"
+          height="12"
+          viewBox="0 0 16 16"
+          fill="none"
+          stroke="currentColor"
+          strokeWidth="2"
+          strokeLinecap="round"
+          strokeLinejoin="round"
+          style={{ color: usageColor, flexShrink: 0 }}
+          aria-hidden="true"
+        >
+          <path d="M9 1L3 9h5l-1 6 6-8H8l1-6z" />
+        </svg>
+        <span style={{ fontWeight: 500, color: "var(--text-2)" }}>
+          {isLoading ? "..." : summary ? formatTokens(summary.totalTokens) : "0"}
+        </span>
+        {!isLoading && currentTier && (
+          <div
+            style={{
+              width: 24,
+              height: 4,
+              borderRadius: 2,
+              background: "var(--bg-mid)",
+              overflow: "hidden",
+              flexShrink: 0,
+            }}
+            aria-hidden="true"
+          >
+            <div
+              style={{
+                width: `${String(pct)}%`,
+                height: "100%",
+                background: usageColor,
+                borderRadius: 2,
+                transition: "width 0.3s ease-out",
+              }}
+            />
+          </div>
+        )}
+        {!isLoading && currentTier && (
+          <span style={{ fontWeight: 600, color: usageColor, minWidth: 32, textAlign: "right" }}>
+            {Math.round(currentTier.percentage)}%
+          </span>
+        )}
+      </button>
+
+      {popoverOpen && (
+        <div
+          role="dialog"
+          aria-label="Usage details"
+          style={{
+            position: "absolute",
+            top: "calc(100% + 8px)",
+            right: 0,
+            width: 280,
+            background: "var(--surface)",
+            border: "1px solid var(--border)",
+            borderRadius: 8,
+            padding: 12,
+            boxShadow: "0 8px 32px rgba(0,0,0,0.3)",
+            zIndex: 200,
+          }}
+        >
+          <div
+            style={{
+              fontSize: "0.83rem",
+              fontWeight: 600,
+              color: "var(--text)",
+              marginBottom: 12,
+              paddingBottom: 8,
+              borderBottom: "1px solid var(--border)",
+            }}
+          >
+            Token Usage
+          </div>
+
+          {isLoading ? (
+            <div
+              style={{
+                textAlign: "center",
+                padding: "20px 0",
+                color: "var(--muted)",
+                fontSize: "0.75rem",
+              }}
+            >
+              Loading usage data…
+            </div>
+          ) : summary ? (
+            <>
+              <div style={{ marginBottom: 12, display: "flex", flexDirection: "column", gap: 8 }}>
+                <div
+                  style={{ display: "flex", justifyContent: "space-between", fontSize: "0.75rem" }}
+                >
+                  <span style={{ color: "var(--muted)" }}>Total Tokens</span>
+                  <span style={{ color: "var(--text)", fontFamily: "var(--mono)" }}>
+                    {formatTokens(summary.totalTokens)}
+                  </span>
+                </div>
+                <div
+                  style={{ display: "flex", justifyContent: "space-between", fontSize: "0.75rem" }}
+                >
+                  <span style={{ color: "var(--muted)" }}>Estimated Cost</span>
+                  <span style={{ color: "var(--text)", fontFamily: "var(--mono)" }}>
+                    ${summary.totalCost.toFixed(2)}
+                  </span>
+                </div>
+                <div
+                  style={{ display: "flex", justifyContent: "space-between", fontSize: "0.75rem" }}
+                >
+                  <span style={{ color: "var(--muted)" }}>Tasks</span>
+                  <span style={{ color: "var(--text)", fontFamily: "var(--mono)" }}>
+                    {summary.taskCount}
+                  </span>
+                </div>
+              </div>
+
+              <div style={{ display: "flex", flexDirection: "column", gap: 10 }}>
+                {tiers.map((tier) => {
+                  const tierPct = Math.min(tier.percentage, 100);
+                  return (
+                    <div key={tier.name}>
+                      <div
+                        style={{
+                          display: "flex",
+                          justifyContent: "space-between",
+                          fontSize: "0.75rem",
+                          marginBottom: 4,
+                        }}
+                      >
+                        <span style={{ color: "var(--text-2)" }}>{tier.name}</span>
+                        <span
+                          style={{
+                            color: getUsageColor(tier.percentage),
+                            fontFamily: "var(--mono)",
+                            fontWeight: 500,
+                          }}
+                        >
+                          {formatTokens(tier.tokens)} / {formatTokens(tier.limit)}
+                        </span>
+                      </div>
+                      <div
+                        style={{
+                          width: "100%",
+                          height: 6,
+                          borderRadius: 3,
+                          background: "var(--bg-mid)",
+                          overflow: "hidden",
+                        }}
+                      >
+                        <div
+                          style={{
+                            width: `${String(tierPct)}%`,
+                            height: "100%",
+                            background: getUsageColor(tier.percentage),
+                            borderRadius: 3,
+                            transition: "width 0.3s ease-out",
+                          }}
+                        />
+                      </div>
+                    </div>
+                  );
+                })}
+              </div>
+
+              <a
+                href="/usage"
+                onClick={(): void => {
+                  setPopoverOpen(false);
+                }}
+                style={{
+                  display: "block",
+                  marginTop: 12,
+                  paddingTop: 8,
+                  borderTop: "1px solid var(--border)",
+                  fontSize: "0.75rem",
+                  color: "var(--primary)",
+                  textDecoration: "none",
+                  textAlign: "center",
+                }}
+                onMouseEnter={(e): void => {
+                  (e.currentTarget as HTMLAnchorElement).style.textDecoration = "underline";
+                }}
+                onMouseLeave={(e): void => {
+                  (e.currentTarget as HTMLAnchorElement).style.textDecoration = "none";
+                }}
+              >
+                View detailed usage →
+              </a>
+            </>
+          ) : (
+            <div
+              style={{
+                textAlign: "center",
+                padding: "20px 0",
+                color: "var(--muted)",
+                fontSize: "0.75rem",
+              }}
+            >
+              No usage data available
+            </div>
+          )}
+        </div>
+      )}
+    </div>
+  );
+}