Improve test coverage for storage package (0 tests, 1106 LOC)

[BrewingCoder]

Area

Backend — API / GraphQL

Category

Test coverage

Description

The storage package handles all session replay data, source maps, and assets across S3 and filesystem backends. It has zero dedicated tests — only indirect coverage via integration tests.

Priority test targets:

1. S3Client / FilesystemClient parity — same inputs produce same outputs
2. Brotli compression round-trip (compress → decompress)
3. Gob encoding round-trip for raw events
4. Session bucket versioning (v2/ prefix for sessions >= 150M)
5. Source map Redis caching (read cached → miss → read from storage)
6. CloudFront URL signing

Structural concerns:

• Single 1,106-line file — should be split into S3Client, FilesystemClient, shared types
• Default filesystem path is /tmp — not durable across restarts
• No streaming — entire files loaded into memory (OOM risk for large sessions)
• Gob encoding for raw events — not inspectable without Go tooling

See src/backend/storage/MODULE.md for full analysis.

Affected Files / Packages

src/backend/storage/storage.go (1,106 lines — single file, 0 tests)

[github-actions]

AI Triage: Storage package lacks test coverage and needs refactoring to split large monolithic file, add unit tests for S3/filesystem parity, compression, and caching logic.

Labels applied: area:backend, tech-debt, priority:high, component:database