Architecture: no disk quota or cleanup for screenshot files

[tkadauke]

Description

Screenshots are stored as PNG files on the server filesystem (lib/session.rb:57). The ScreenshotFile class manages retention via retain/release reference counting, but there is no:

• Disk usage cap per account
• Maximum number of screenshots per health check
• Age-based cleanup policy
• Compression beyond pngcrush

Full-page screenshots at high resolution can be 500KB–2MB each. With 1-minute checks and multiple TakeScreenshotStep steps, a single health check can generate gigabytes per day.

Impact

• Disk exhaustion on the host server causes all checks to fail.
• No multi-tenant fairness: one account can consume all disk space.
• No cost visibility for screenshot storage.

Suggested approach

1. Add a max_screenshots setting per health check or account.
2. Implement a background job that prunes screenshots older than N days.
3. Consider storing screenshots in object storage (S3, GCS) instead of local filesystem.
4. Add disk usage monitoring/alerting.

Effort: medium