fix(email): use Gmail REST API for sending on OAuth accounts

[zbigniewsobiecki]

Problem

SMTP port 465 is blocked in the worker container, causing ReplyToEmail and SendEmail gadget calls on Gmail OAuth accounts to silently hang for 30 s before the gadget timeout fires. Confirmed in the car-dealership email-joke run: all three ReplyToEmail calls timed out at exactly 30 000 ms with a cryptic "Gadget exceeded timeout" error.

Root cause: nodemailer.createTransport() has no connection-level timeout, so the gadget outer timer is the only kill-switch. IMAP (port 993) is not affected.

Solution

For authMethod === 'oauth' accounts, route sendEmail() and replyToEmail() through the Gmail REST API (users.messages.send) instead of SMTP. Password/SMTP accounts are completely unaffected.

• MIME building: uses nodemailer's streamTransport mode — in-process, zero network — to produce correctly-encoded RFC 822 bytes without any custom MIME logic
• Auth: OAuth2Client.setCredentials() passes the existing access token directly; no re-auth needed (token refresh is already handled in oauth.ts)
• Threading: replyViaGmailApi() reads the original message via IMAP (unchanged), then builds correct In-Reply-To and References headers before sending via REST

Changes

File	Change
src/email/gmail/send.ts	New — sendViaGmailApi() and replyViaGmailApi()
src/email/client.ts	Branch on authMethod in sendEmail() and replyToEmail()
tests/unit/email/gmail/send.test.ts	New — 8 unit tests
package.json / package-lock.json	Add @googleapis/gmail

Tests

8 new unit tests cover:

• ✅ Success path: correct messageId and accepted array
• ✅ Raw payload is valid base64url and passed to Gmail API
• ✅ Reply-to-sender: single recipient, Re: prefix added
• ✅ Reply-all: self excluded, original To + CC included
• ✅ No double Re: prefix when subject already starts with Re:
• ✅ Error propagation from the Gmail API (both send and reply)

Verification

# Re-trigger on prod after deploy:
cascade runs trigger --project car-dealership --agent-type email-joke
# Wait ~2 min, then:
cascade runs list --project car-dealership --agent-type email-joke --limit 3
cascade runs logs <new-run-id>
# Expect: ReplyToEmail gadget results succeed (no 30 s timeout), status=completed

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