[BUG] Scheduled triggers API returns HTTP 500 on all endpoints (list, get, run), create returns 200 but trigger not persisted

Description

The scheduled triggers API (RemoteTrigger) is returning HTTP 500 errors on all endpoints. A create call returns 200 but the trigger does not appear in the UI and cannot be retrieved via the API.

Steps to reproduce

1. Call RemoteTrigger with action: "list" → HTTP 500
2. Call RemoteTrigger with action: "create" with valid body → HTTP 200, returns trigger ID trig_01WzbVtuNRGjWeGgdCZ7dZim
3. Call RemoteTrigger with action: "get", trigger_id from step 2 → HTTP 500
4. Call RemoteTrigger with action: "run", trigger_id from step 2 → HTTP 500
5. Visit https://claude.ai/code/scheduled → Shows "Failed to load scheduled tasks"
6. Created trigger does not appear in the UI

Expected behavior

• All API endpoints should return valid responses
• Created trigger should appear in the UI and be runnable

Environment

• Claude Code CLI (macOS)
• Model: claude-opus-4-6 (1M context)
• Date: April 4, 2026
• Environment ID: env_0194sBUD5Cscjh6VnbdiLhsx (Default, anthropic_cloud)

Error responses

All failing endpoints return the same error format:

{"error": {"message": "An internal server error occurred", "type": "api_error"}, "type": "error"}

Related issues

• #42662 — Scheduled triggers not auto-running, manual trigger returns 500
• #42582 — Remote Trigger /run returns HTTP 500, trigger auto-disables
• #43409 — Web UI "Failed to load scheduled tasks"