feat: smart @mention booking flow with multi-attendee support

[dhairyashiil]

feat: smart @mention booking flow with multi-attendee support

Summary

Upgrades the AI agent's booking flow so @Cal.com book a meeting with @bailey and @Keith Williams works end-to-end on Slack and Telegram — with clarification-first logic, multi-attendee resolution, and a fast-path for fully-specified requests.

System prompt changes (lib/agent.ts):

• Rewrites the booking flow from "pick best match silently" to a 5-step clarification-first flow: resolve attendees → resolve event type → resolve date/time → confirm → multi-attendee handling
• Adds a fast path that skips the confirmation round-trip when all details are unambiguous and the user says "go ahead" / "book it"
• Relaxes CRITICAL RULES: allows re-calling check_availability for alternative slots, allows sequential tool calls during booking flows, allows same tool with different arguments (e.g. two lookup_platform_user calls for two users)

Tool & API changes:

• book_meeting — adds optional guestEmails: string[] field, passed as guests in the POST /v2/bookings payload (Strategy A: email-only additional attendees in one call)
• add_booking_attendee (new) — calls POST /v2/bookings/{uid}/attendees to add a full attendee record with name + timezone after booking (Strategy B: for Slack @mentions resolved via lookup_platform_user)
• CreateBookingInput — adds guests?: string[]
• AddAttendeeInput (new type) + addBookingAttendee() client function
• check_availability — description updated to allow re-calls
• MAX_STEPS — bumped 10 → 15 to accommodate multi-attendee flows

Files changed: lib/agent.ts, lib/calcom/client.ts, lib/calcom/types.ts

Review & Testing Checklist for Human

• Verify POST /v2/bookings/{uid}/attendees endpoint exists in the Cal.com v2 API and accepts { name, email, timeZone }. The addBookingAttendee function assumes this endpoint — if it doesn't exist, the add_booking_attendee tool will always error at runtime.
• Verify guests field is accepted by POST /v2/bookings. The book_meeting tool now passes guests: ["email@example.com"] — confirm the Cal.com API accepts this and actually adds them to the calendar event.
• Manual Slack test: Try @Cal.com book a meeting with @someone and verify the agent asks for event type and time instead of silently picking. Try with two @mentions to test multi-attendee flow.
• Manual Slack fast-path test: Try @Cal.com book a 30 min meeting with @someone at 3pm tomorrow, go ahead — should book immediately without asking for confirmation.
• Manual Telegram test: Try book a meeting with John (john@example.com) — verify it asks for event type and time, then confirms before booking.
• Review system prompt for contradictions between the new booking flow instructions and the relaxed CRITICAL RULES (especially rules 3, 4, 6).

Notes

• All type errors in the changed files are pre-existing (missing ai/chat/zod module declarations and Node types — these resolve when dependencies are installed). No new type errors introduced.
• The prompt changes are the highest-risk area since LLM behavior is non-deterministic and can't be verified by CI.
• No automated tests added — the companion repo doesn't have an agent test suite, and the changes are primarily prompt engineering + thin API wrappers.

Link to Devin Session: https://app.devin.ai/sessions/f69e6c70ee544da7b5b6e91a9b73d29b
Requested by: @dhairyashiil

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