⚠️ Potential issue | 🟠 Major

Include reporting period in the idempotency key.

The current idempotency key format (${program.id}-${partner.id}) lacks a temporal component, meaning the same key is reused every month. While email providers typically expire idempotency keys after 24 hours, this creates two concerns:

1. If the cron job needs to be re-run within the idempotency TTL window (e.g., to fix a bug or update data), the duplicate key will prevent emails from being resent to partners.
2. The intent isn't explicit—each monthly report is a distinct email and should have a unique key.

Including the reporting period makes the key unique per report cycle and more robust.

Apply this diff to include the reporting period:

+      const reportingMonth = format(currentMonth, "MMM yyyy");
+
       await sendBatchEmail(
         summary.map(({ partner, ...rest }) => ({
           subject: `Your ${reportingMonth} performance report for ${program.name} program`,
           to: partner.email!,
           react: PartnerProgramSummary({
             program,
             partner,
             ...rest,
             reportingPeriod: {
               month: reportingMonth,
               start: currentMonth.toISOString(),
               end: endOfMonth(currentMonth).toISOString(),
             },
           }),
           variant: "notifications",
           headers: {
-            "Idempotency-Key": `${program.id}-${partner.id}`,
+            "Idempotency-Key": `${program.id}-${partner.id}-${format(currentMonth, "yyyy-MM")}`,
           },
         })),
       );

Note: Move the reportingMonth declaration above the sendBatchEmail call as shown, since it's currently declared at line 317 but needs to be accessible here. Alternatively, use format(currentMonth, "yyyy-MM") directly in the idempotency key as suggested above.

Committable suggestion skipped: line range outside the PR's diff.

In apps/web/app/(ee)/api/cron/partner-program-summary/route.ts around lines 334
to 336, the idempotency key currently uses `${program.id}-${partner.id}` and
must include the reporting period so each monthly report is unique; move the
reportingMonth declaration (currently at ~line 317) above the sendBatchEmail
call and change the header to include it (e.g.
`${program.id}-${partner.id}-${reportingMonth}`) or inline the formatted month
with format(currentMonth, "yyyy-MM") in the Idempotency-Key; ensure the
reportingMonth/format expression is defined before the headers and preserve
existing string interpolation and header structure.