Implement proxy-download mode in the mock AWS driver

[bauerpawel]

Description

The real S3 driver supports a ProxyDownload config option (stream the file content through the server instead of redirecting to a presigned URL), but the mock driver used for awsmock-tagged tests always redirected regardless of that setting — so the proxy-download code path had no test coverage at all.

Mirrors the real implementation in the mock: when ProxyDownload is set, reads the file content from a local test fixture at data/<sha1> (the same convention Stream() already uses) and streams it to the response instead of redirecting.

Type of Change

• New feature (non-breaking change which adds functionality)

Technical Details

• Database changes: No
• Storage backend affected: S3
• Usage of AI: Yes — developed with Claude Code as a pair-programming assistant. I reviewed and tested all changes before submitting.

How Has This Been Tested?

• Unit Tests: Added Aws_mock_test.go covering proxy-download streaming (happy path), a missing on-disk fixture (error path), and confirming the existing redirect behavior still works when ProxyDownload is off. All pass in isolation and as part of the full suite.
• Environment: Windows 11

Checklist

• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation. (n/a — internal test-infrastructure change, ProxyDownload itself already existed and is documented)
• My changes generate no new warnings.

🤖 Generated with Claude Code

https://claude.ai/code/session_0168YUwGEzEHTqd9CwzXE53d