[Spike] Time Stalwart v0.15 to v0.16 export/import with migrate_v016.py

Overview

Before committing to the downtime-tolerant migration approach, run a timed end-to-end test of the data export/import path using the official migrate_v016.py script. The goal is to measure how long the export and import take against real production-scale data, so we can size the migration window realistically.

Steps

1. Download the migration script:

   curl -o migrate_v016.py https://raw.githubusercontent.com/stalwartlabs/stalwart/refs/heads/main/resources/scripts/migrate_v016.py
   

2. Export data from the existing prod system (time this step):

   python migrate_v016.py dump --url $OLD_STALWART_URL --username $OLD_STALWART_USER --password $OLD_STALWART_PASSWORD --settings settings.json --principals principals.json
   

3. Convert the export into an importable format (time this step):

   python migrate_v016.py convert --settings settings.json --principals principals.json --config config.json --output export.json
   

4. Import into a fresh v0.16 system (time this step):

   stalwart-cli apply --file /path/to/export.json
   

Notes

• Credentials are supplied via environment variables (OLD_STALWART_URL, OLD_STALWART_USER, OLD_STALWART_PASSWORD) and must not be committed or pasted into this issue.
• Record wall-clock time for each step, plus the sizes of settings.json, principals.json, and export.json.

Acceptance Criteria

• All four steps run successfully end-to-end
• Per-step durations recorded in a comment on this issue
• Artifact sizes noted (settings.json, principals.json, export.json)