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feat(emails): optional idempotency_key makes a replayed send deliver once #807

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24 changes: 24 additions & 0 deletions lib/emails/__tests__/processAndSendEmail.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@ describe("processAndSendEmail", () => {
subject: "Test",
html: expect.stringContaining("Hello world"),
}),
undefined,
);
});

Expand All @@ -56,6 +57,7 @@ describe("processAndSendEmail", () => {
expect.objectContaining({
html: expect.stringContaining("<h1>HTML body</h1>"),
}),
undefined,
);
});

Expand All @@ -72,6 +74,7 @@ describe("processAndSendEmail", () => {
expect.objectContaining({
cc: ["cc@example.com"],
}),
undefined,
);
});

Expand All @@ -91,6 +94,7 @@ describe("processAndSendEmail", () => {
expect.objectContaining({
html: expect.stringContaining("Test Artist"),
}),
undefined,
);
});

Expand Down Expand Up @@ -129,4 +133,24 @@ describe("processAndSendEmail", () => {
expect(result.error).toContain("Rate limited");
}
});

it("forwards idempotencyKey to Resend so a replayed send delivers once (chat#1918)", async () => {
mockSendEmailWithResend.mockResolvedValue({ id: "resend-1" });
await processAndSendEmail({
to: ["a@b.com"],
subject: "S",
text: "body",
idempotencyKey: "chat_1:msg_2",
});
expect(mockSendEmailWithResend).toHaveBeenCalledWith(
expect.anything(),
expect.objectContaining({ idempotencyKey: "chat_1:msg_2" }),
);
});

it("omits Resend options entirely when no idempotencyKey is given", async () => {
mockSendEmailWithResend.mockResolvedValue({ id: "resend-2" });
await processAndSendEmail({ to: ["a@b.com"], subject: "S", text: "body" });
expect(mockSendEmailWithResend).toHaveBeenCalledWith(expect.anything(), undefined);
});
});
27 changes: 18 additions & 9 deletions lib/emails/processAndSendEmail.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,12 @@ export interface ProcessAndSendEmailInput {
html?: string;
headers?: Record<string, string>;
room_id?: string;
/**
* Makes the send exactly-once for a retried or replayed caller. Scheduled

@cubic-dev-ai cubic-dev-ai Bot Jul 31, 2026

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P2: The new comment overstates the guarantee: a replay after Resend’s 24-hour retention window can deliver again; describe this as deduplication within Resend’s 24-hour window or add durable deduplication for longer-lived retries.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At lib/emails/processAndSendEmail.ts, line 18:

<comment>The new comment overstates the guarantee: a replay after Resend’s 24-hour retention window can deliver again; describe this as deduplication within Resend’s 24-hour window or add durable deduplication for longer-lived retries.</comment>

<file context>
@@ -14,6 +14,12 @@ export interface ProcessAndSendEmailInput {
   headers?: Record<string, string>;
   room_id?: string;
+  /**
+   * Makes the send exactly-once for a retried or replayed caller. Scheduled
+   * runs re-execute on crash or redeploy and would otherwise deliver the same
+   * report again (chat#1918). Forwarded to Resend, which dedupes on it.
</file context>

* runs re-execute on crash or redeploy and would otherwise deliver the same
* report again (chat#1918). Forwarded to Resend, which dedupes on it.
*/
idempotencyKey?: string;
}

export interface ProcessAndSendEmailSuccess {
Expand All @@ -39,7 +45,7 @@ export type ProcessAndSendEmailResult = ProcessAndSendEmailSuccess | ProcessAndS
export async function processAndSendEmail(
input: ProcessAndSendEmailInput,
): Promise<ProcessAndSendEmailResult> {
const { to, cc = [], subject, text, html = "", headers = {}, room_id } = input;
const { to, cc = [], subject, text, html = "", headers = {}, room_id, idempotencyKey } = input;

const roomData = room_id ? await selectRoomWithArtist(room_id) : null;
const footer = getEmailFooter(room_id, roomData?.artist_name || undefined);
Expand All @@ -51,14 +57,17 @@ export async function processAndSendEmail(
// card, DESIGN.md font stack, and the existing footer as the layout footer.
const htmlWithLayout = renderEmailLayout({ bodyHtml, footerHtml: footer });

const result = await sendEmailWithResend({
from: RECOUP_FROM_EMAIL,
to,
cc: cc.length > 0 ? cc : undefined,
subject,
html: htmlWithLayout,
headers,
});
const result = await sendEmailWithResend(
{
from: RECOUP_FROM_EMAIL,
to,
cc: cc.length > 0 ? cc : undefined,
subject,
html: htmlWithLayout,
headers,
},
idempotencyKey ? { idempotencyKey } : undefined,

@cubic-dev-ai cubic-dev-ai Bot Jul 31, 2026

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P2: An explicitly supplied empty idempotency_key is silently downgraded to a non-idempotent send, allowing a retry to duplicate delivery; use an explicit undefined check here and reject empty keys in the request schema.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At lib/emails/processAndSendEmail.ts, line 69:

<comment>An explicitly supplied empty `idempotency_key` is silently downgraded to a non-idempotent send, allowing a retry to duplicate delivery; use an explicit `undefined` check here and reject empty keys in the request schema.</comment>

<file context>
@@ -51,14 +57,17 @@ export async function processAndSendEmail(
+      html: htmlWithLayout,
+      headers,
+    },
+    idempotencyKey ? { idempotencyKey } : undefined,
+  );
 
</file context>
Suggested change
idempotencyKey ? { idempotencyKey } : undefined,
idempotencyKey !== undefined ? { idempotencyKey } : undefined,

);

if (result instanceof NextResponse) {
const data = await result.json();
Expand Down
2 changes: 2 additions & 0 deletions lib/emails/sendEmailHandler.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ export async function sendEmailHandler(request: NextRequest): Promise<NextRespon
headers = {},
chat_id,
accountId,
idempotency_key,
} = validated.data;
const result = await processAndSendEmail({
to,
Expand All @@ -39,6 +40,7 @@ export async function sendEmailHandler(request: NextRequest): Promise<NextRespon
html,
headers,
room_id: chat_id,
idempotencyKey: idempotency_key,
});

if (result.success === false) {
Expand Down
4 changes: 4 additions & 0 deletions lib/emails/validateSendEmailBody.ts
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Expand Up @@ -19,6 +19,10 @@ export const sendEmailBodySchema = z
html: z.string().optional(),
headers: z.record(z.string(), z.string()).default({}).optional(),
chat_id: z.string().optional(),
idempotency_key: z

@cubic-dev-ai cubic-dev-ai Bot Jul 31, 2026

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P2: The new idempotency_key field is added to the validation schema but the validation test file doesn't cover it. The "all optional fields" test no longer exercises all optional fields now that idempotency_key exists, and there are no tests for the max(256) constraint or for accepting a valid key. Adding test coverage for the schema-level validation would catch regressions in the field's constraints.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At lib/emails/validateSendEmailBody.ts, line 22:

<comment>The new `idempotency_key` field is added to the validation schema but the validation test file doesn't cover it. The "all optional fields" test no longer exercises all optional fields now that `idempotency_key` exists, and there are no tests for the `max(256)` constraint or for accepting a valid key. Adding test coverage for the schema-level validation would catch regressions in the field's constraints.</comment>

<file context>
@@ -19,6 +19,10 @@ export const sendEmailBodySchema = z
     html: z.string().optional(),
     headers: z.record(z.string(), z.string()).default({}).optional(),
     chat_id: z.string().optional(),
+    idempotency_key: z
+      .string()
+      .max(256, "idempotency_key must be at most 256 characters")
</file context>

.string()
.max(256, "idempotency_key must be at most 256 characters")
.optional(),
account_id: z.string().uuid("account_id must be a valid UUID").optional(),
})
// Guard: never send an empty/footer-only email. A malformed or empty body
Expand Down
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