diff --git a/app/api/mobile/engagement/trend/route.ts b/app/api/mobile/engagement/trend/route.ts
new file mode 100644
index 0000000..653ccd0
--- /dev/null
+++ b/app/api/mobile/engagement/trend/route.ts
@@ -0,0 +1,92 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { requireAuth } from '@/lib/auth-utils';
+import { postgresClient } from '@/lib/services/postgres-client';
+
+export interface SparklinePoint {
+  date: string;  // ISO date string "YYYY-MM-DD"
+  hours: number; // total Autotask hours for that day (0 if no entries)
+}
+
+export interface EngagementTrendResponse {
+  points: SparklinePoint[]; // D7 → 7, D30 → 30, D90 → 90 points
+}
+
+const ALLOWED_PERIODS = ['D7', 'D30', 'D90'] as const;
+type AllowedPeriod = (typeof ALLOWED_PERIODS)[number];
+const PERIOD_DAYS: Record<AllowedPeriod, number> = { D7: 7, D30: 30, D90: 90 };
+
+function parsePeriod(raw: string | null): AllowedPeriod | null {
+  if (!raw) return 'D30'; // default per D-04
+  return (ALLOWED_PERIODS as readonly string[]).includes(raw) ? (raw as AllowedPeriod) : null;
+}
+
+export async function GET(request: NextRequest): Promise<NextResponse> {
+  const { error: authError } = await requireAuth();
+  if (authError) return authError;
+
+  const { searchParams } = request.nextUrl;
+  const period = parsePeriod(searchParams.get('period'));
+  if (period === null) {
+    return NextResponse.json(
+      { error: 'Invalid period', message: "period must be one of 'D7', 'D30', 'D90'" },
+      { status: 400 },
+    );
+  }
+
+  const days = PERIOD_DAYS[period];
+  // T-07-03 mitigation: period whitelist bounds the date range to max 90 days.
+  // No user-supplied row-count parameter — generate_series produces at most 90 rows.
+
+  try {
+    // generate_series ensures every day in the range has a row even when zero hours
+    // were logged (D-15: continuous series, no gaps in the sparkline).
+    // ${days - 1} is interpolated, NOT parameterized — safe because period is whitelisted
+    // to one of ['D7','D30','D90'] and days comes from a static map (not user input).
+    const sql = `
+      WITH day_series AS (
+        SELECT generate_series(
+          (CURRENT_DATE - INTERVAL '${days - 1} days')::date,
+          CURRENT_DATE,
+          INTERVAL '1 day'
+        )::date AS day
+      ),
+      daily_hours AS (
+        SELECT te.entry_date::date AS day, COALESCE(SUM(te.hours_worked), 0) AS hours
+          FROM time_entries te
+          JOIN resources r ON r.id = te.resource_id
+            AND (r.is_deleted = false OR r.is_deleted IS NULL)
+          JOIN graph_users gu ON LOWER(gu.email) = LOWER(r.email)
+         WHERE te.entry_date >= CURRENT_DATE - INTERVAL '${days - 1} days'
+           AND te.entry_date <= CURRENT_DATE
+           AND (te.is_deleted = false OR te.is_deleted IS NULL)
+           AND gu.account_enabled = true
+           AND LOWER(gu.email) LIKE '%@wulfconsulting.%'
+           AND LOWER(gu.email) NOT LIKE '%#ext#%'
+         GROUP BY te.entry_date::date
+      )
+      SELECT to_char(ds.day, 'YYYY-MM-DD') AS date,
+             COALESCE(dh.hours, 0)::numeric AS hours
+        FROM day_series ds
+        LEFT JOIN daily_hours dh ON dh.day = ds.day
+       ORDER BY ds.day ASC
+    `;
+
+    const result = await postgresClient.query(sql);
+
+    const points: SparklinePoint[] = result.rows.map((row) => ({
+      date: String(row.date),
+      hours: Math.round(parseFloat(row.hours ?? '0') * 10) / 10,
+    }));
+
+    return NextResponse.json({ points } satisfies EngagementTrendResponse);
+  } catch (error) {
+    console.error('GET /api/mobile/engagement/trend failed:', error);
+    return NextResponse.json(
+      {
+        error: 'Failed to fetch engagement trend',
+        message: error instanceof Error ? error.message : 'unknown',
+      },
+      { status: 500 },
+    );
+  }
+}