Add support for v3 schedules API

[FrancesCoronel]

Summary

The MCP server currently only supports classic (v2) schedules via the /schedules and /schedules/{id} REST API endpoints. PagerDuty's newer v3 schedules — which use the /v3/schedules/... API family — are completely invisible to the MCP server.

Problem

When a schedule is created using PagerDuty's newer scheduling system (v3), the MCP server cannot:

• Read the schedule (get_schedule returns 404)
• List it (list_schedules omits it entirely)
• Update it (update_schedule fails)
• Parse escalation policy references to it (the schedule_v3_reference type causes a Pydantic validation error in get_escalation_policy)

This means any organization using v3 schedules cannot manage them through the MCP server at all.

How to reproduce

1. Create a schedule using PagerDuty's newer scheduling UI (which creates a v3 schedule)
2. Try to access it via the MCP server's get_schedule tool — returns 404
3. Try list_schedules — the schedule does not appear
4. If the schedule is referenced in an escalation policy, get_escalation_policy fails with:

   Input should be 'user_reference' or 'schedule_reference'
   [type=literal_error, input_value='schedule_v3_reference', input_type=str]
   

Expected behavior

The MCP server should support v3 schedules, including:

• Listing and reading v3 schedules
• Creating and updating v3 schedules (with their rotations, events, custom shifts, overrides)
• Properly handling schedule_v3_reference types in escalation policies

Context

• The v3 schedule API lives at /v3/schedules/... with a different data model (schedules → rotations → events → custom shifts → overrides)
• PagerDuty's Go client library (go-pagerduty/schedule_v3.go) fully implements the v3 API
• PagerDuty's Terraform provider already supports v3 schedules via the pagerduty_schedulev2 resource
• The v3 API appears stable and actively used

Workaround

Currently the only workaround is to recreate the schedule as a classic (v2) schedule, or manage v3 schedules manually through the PagerDuty UI.

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